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Salvador Cob, S., Yeme, C., Hofs, B., Cornelissen, E.R., Vries, D., Genceli Güner, F.E., Witkamp, G.J.
Towards zero liquid discharge in the presence of silica: Stable 98% recovery in nanofiltration and reverse osmosis
(2014) Separation and Purification Technology, 140, pp. 23-31.
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ABSTRACT: Silica scaling can be a limiting factor for membrane treatment at very high recoveries. In this work the feasibility of reaching very high recoveries (≥98%) was investigated in a pilot plant consisting of cation exchange pretreatment, nanofiltration (NF) and reverse osmosis (RO), with pretreated ground water as feed water, with no aluminum detected. Experiments were carried out at total recovery (NF + RO) of 98% and 99% and with the addition of two different antiscalants at 99% recovery. 98% recovery was possible during 23 days of operation with only a minor decrease in the membrane permeability. At 99% recovery SEM-EDX analysis showed that silica and ironsilicate scaling occurred in the RO membrane, and strongly decreased the membrane permeability. The addition of antiscalants to the pilot plant did not prevent the occurrence of scaling. The laboratory beaker experiments did not prove the efficiency of the antiscalants either. The mean residence time of water in the pilot plant was estimated at 1 h. The occurrence of scaling in the presence of antiscalants can be attributed to factors such as the long residence time in the pilot plant, which is probably longer than the induction time, and the relatively high concentration of particulate iron in the feed water.
Fang, C., Lu, X., Buijs, W., Fan, Z., Genceli Güner, F.E., van Huis, M.A., Witkamp, G.-J., Vlugt, T.J.H.
Crystal structure, stability, and electronic properties of hydrated metal sulfates MSO4(H2O)n (M=Ni, Mg; n=6, 7) and their mixed phases: A first principles study
(2015) Chemical Engineering Science, 121, pp. 77-86.
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ABSTRACT: Removal of Mg from hydrated Ni sulfates has long been a problem in the industrial purification process of hydrated Ni sulfates. In this work, we have investigated this industrial problem using state-of-the-art molecular simulations. Periodic Density Functional Theory (DFT) and cluster DFT calculations are used to study the crystal structures and phase stability of the hexahydrated and heptahydrated Ni and Mg sulfates and their mixed phases. The calculated lattice parameters of MSO4(H2O)n (M=Ni, Mg; n=6, 7) crystals are in good agreement with available experimental data. The relative energy differences of the mixed phase for both hexahydrated and heptahydrated Ni/Mg sulfates obtained from both the periodic and cluster DFT calculations are generally less than kT (25.8meV, T=300K), indicating that a continuous solid solution is formed. We also investigated the Bader charges and electronic structures of the hexahydrated and heptahydrated Ni/Mg sulfates using the periodic DFT calculations. The energy band gaps of the hexahydrated and heptahydrated Ni and Mg sulfates were predicted by first-principles calculations. Large energy band gaps of about ~5.5eV were obtained from the DFT-GGA calculations for hydrated Mg sulfates, and band gaps of about ~5.1eV were obtained by the DFT-GGA+U calculations for hydrated Ni sulfates.
Salvador Cob, S., Beaupin, C., Hofs, B., Nederlof, M.M., Harmsen, D.J.H., Cornelissen, E.R., Zwijnenburg, A., Genceli Güner, F.E., Witkamp, G.J.
Corrigendum to "Silica and silicate precipitation as limiting factors in high-recovery reverse osmosis operations" [J. Membr. Sci. 423-424 (2012) 1-10]
(2015) Journal of Membrane Science, 473, p. 333.
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Salvador Cob, S., Hofs, B., Maffezzoni, C., Adamus, J., Siegers, W.G., Cornelissen, E.R., Genceli Güner, F.E., Witkamp, G.J.
Silica removal to prevent silica scaling in reverse osmosis membranes
(2014) Desalination, 344, pp. 137-143.
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ABSTRACT: Reverse osmosis membranes are increasingly used in drinking water treatment. However, the production of a concentrate stream is the main disadvantage of its application. Increasing the recovery of the membranes in order to have the smallest amount of concentrate possible is an attractive approach. In the absence of bivalent cations in the feed water, silica and silica-derived precipitants are limiting factors in high-recovery reverse osmosis operations. The removal of silica in a separate pretreatment process might be the solution. Several methods were tested to remove silica. Precipitation of silica with Fe(OH)3, Al(OH)3 and silica gel was investigated, and also the removal of silica using a strongly basic anion (SBA) exchange resin.Al(OH)3 was the most effective precipitant for silica, removing nearly all of the molecularly dissolved silica. However, a residual amount of aluminum remained in solution, and aluminosilicate colloids were not removed. The use of the SBA exchange resin also showed a good performance, removing up to 94% of the silica. However, further investigations, such as checking whether the residual small amounts of silica and aluminum can still cause scaling in the membrane, need to be conducted. © 2014 Elsevier B.V.
Salvador Cob, S., Genceli Güner, F.E., Hofs, B., van Spronsen, J., Witkamp, G.J.
Three strategies to treat reverse osmosis brine and cation exchange spent regenerant to increase system recovery
(2014) Desalination, 344, pp. 36-47.
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ABSTRACT: Concentrate streams from industrial processes entail an important risk for the environment, as they are often discharged into it. Therefore, efforts must be made to reduce the load of contaminants discharged to the environment. Eutectic freeze crystallization (EFC) is a novel technique which allows separation of salts and water from aqueous streams. In this research, three treatment options for reverse osmosis (RO) concentrate and cation exchange (CIEX) spent regenerant are investigated.First, application of EFC to RO concentrate was investigated. The stream was rich in HCO3 - and Na+. Application of EFC to this solution, led to the formation of ice and NaHCO3 at -3.9°C with 5.8wt.% NaHCO3.Second, precipitation of CaCO3 by mixing the RO concentrate with the CIEX regenerant in a ratio of 2.8:1 and adjusting the pH to 11 was investigated. A 0.25M NaCl solution remained after the treatment, which upon concentration could be used to regenerate the resin.Third, application of EFC to a synthetic CIEX regenerant was also investigated. The multicomponent solution contained NaCl, MgCl2 and CaCl2. Upon EFC treatment, ice formed first and then NaCl·2H2O at -29°C. The composition of eutectic point at -29.4°C was 2.48wt.% Na and 15.85wt.% Cl. © 2014 Elsevier B.V.
Sutanto, S., Dutschk, V., Mankiewicz, J., Van Roosmalen, M., Warmoeskerken, M.M.C.G., Witkamp, G.-J.
CO2 dry cleaning: Acoustic cavitation and other mechanisms to induce mechanical action
(2014) Journal of Supercritical Fluids, 89, pp. 1-7.
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ABSTRACT: High pressure carbon dioxide (CO2) is a potential solvent for textile dry cleaning. However, the particulate soil (e.g. clay, sand) removal in CO2 is generally insufficient. Since cavitation has been proven to be beneficial in other CO2 cleaning applications, this study aims to investigate the possibility of improving the performance of CO2 textile dry cleaning by using ultrasound or other mechanisms to induce the mechanical action such as bubble spray and jet spray. In the experiments, several types of textiles soiled with a mixture of motor oil and soot were cleaned using 1 L and 90 L CO2 dry cleaning set-ups. Using either ultrasound, stirring, liquid spray or bubble spray does not give a significant improvement on particulate soil removal from textile. It was also found that the additional use of ClipCOO detergent does not give a significant improvement on particulate soil removal either. The cleaning performance of CO2 is 50% lower than that of PER and thus another method to increase the particulate soil removal in CO2 textile dry cleaning still needs to be developed. © 2014 Elsevier B.V.
Sutanto, S., Van Roosmalen, M.J.E., Witkamp, G.J.
Mechanical action in CO2 dry cleaning
(2014) Journal of Supercritical Fluids, 93, pp. 138-143.
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ABSTRACT: High-pressure carbon dioxide (CO2) is a potential alternative for perchloroethylene (PER), a common but harmful textile dry cleaning solvent. Previous studies have indicated that the particulate soil removal with CO2 is lower compared to that with PER, because of the low amount of mechanical action in CO2. It is the objective of this study to get more insight in the influence of various types of mechanical action on the cleaning results in CO2 dry cleaning. In the experiments, various mechanisms of mechanical action, such as rotating drum, CO2 spray, and ultrasound were investigated. Several types of textiles stained with different kinds of particulate soils were cleaned using 25 L and 90 L CO2 dry cleaning set-ups. The washing results show that liquid CO2 spray may be a suitable additional mechanism to provide textile movement. The average CPI of CO2 over all soils using the best combination of commercial machine and process was still 25% lower than the results with PER and 18% lower than the results with water, but 11% higher than K4 solvent while the average redeposition level was significantly lower, showing that CO2 has a good prospect as an alternative solvent to replace PER. An endoscopic camera has been installed in the 25 L set-up to get an insight in the textile movement inside the rotating drum. The results show that no plug formation occurs and the textile movement in CO2 is sluggish, which means that the mechanical movement of textile in CO2 dry cleaning does not follow the simplified tumbling-movement model which was developed in a previous study, and the mechanical action is much less than predicted.
Rachmaniah, O., Choi, Y.H., Arruabarrena, I., Vermeulen, B., Van Spronsen, J., Verpoorte, R., Witkamp, G.-J.
Environmentally benign supercritical CO2 extraction of galanthamine from floricultural crop waste of Narcissus pseudonarcissus
(2014) Journal of Supercritical Fluids, 93, pp. 7-19.
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ABSTRACT: The influence of diverse factors on the supercritical fluid extraction (SFE) with supercritical CO2 (scCO2) of galanthamine from bulbs of Narcissus pseudonarcissus cv. Carlton was investigated. The parameters that were studied were CO2 density (temperature and pressure), flow rate and plant material particle size and pre-treatment. The highest yield (303 μg/g) was achieved by extracting 53-1000 μm particle-size powdered dried bulb material moistened with NH4OH (25%, v/v) at 70 °C, 220 bar (690 kg/m3) for 3 h. Other N. pseudonarcissus alkaloids such as O-methyllycorenine and haemanthamine were also obtained. N. pseudonarcissus alkaloids as free bases are highly soluble in CO2 at a high pH as opposed to the slightly soluble salt form in which they are generally found in plants. Therefore, plant material pre-treatment with a base is an essential step for galanthamine extraction. Scanning electron microscope (SEM) results also revealed that the desorption of N. pseudonarcissus alkaloids from the plant material rather than the solubility of the alkaloids in the scCO2 plays a major role in this scCO2 extraction. This extraction method has a good potential for industrial application.
Wagterveld, R.M., Yu, M., Miedema, H., Witkamp, G.J.
Polymorphic change from vaterite to aragonite under influence of sulfate: The "morning star" habit
(2014) Journal of Crystal Growth, 387, pp. 29-35.
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ABSTRACT: The presence of sulfate in reverse osmosis drinking water concentrate and its effect on calcium carbonate precipitation was studied, notably the overall kinetics of CaCO3 formation and the types of polymorphs formed. CaCO3 formation slows down with increasing sulfate concentration and the preferential polymorph shifts from vaterite to aragonite with increasing sulfate concentration. With this polymorphic change, a new combined habit is observed where aragonite spikes grow on top of vaterite ("morning star" habit). The presence of a moderate magnesium concentration results in the shift of vaterite to aragonite at relatively low sulfate concentrations; where sulfate and magnesium appear to have an additive effect. Without magnesium, spikes on top of vaterite were also observed, but only at relatively high sulfate concentration. Without the presence of magnesium, single crystals of aragonite were not found. © 2013 Elsevier B.V.
Kappel, C., Yasadi, K., Temmink, H., Metz, S.J., Kemperman, A.J.B., Nijmeijer, K., Zwijnenburg, A., Witkamp, G.-J., Rijnaarts, H.H.M.
Electrochemical phosphate recovery from nanofiltration concentrates
(2013) Separation and Purification Technology, 120, pp. 437-444.
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ABSTRACT: The high total phosphorus content of raw domestic wastewater with its significant eutrophication potential offers an excellent possibility for phosphate recovery. Continuous recirculation of NF concentrate to an MBR and simultaneous phosphate recovery from the NF concentrate can be applied to produce reusable water, recovering phosphates, while at the same time decreasing the scaling potential of the recirculated NF concentrate, prolonging the retention times of slowly biodegradable soluble compounds (e.g. micropollutants) and recirculating multivalent cations to promote the bio-flocculation. Here we introduce an electrochemical system to recover phosphates. An electrochemical cell was divided into an anode and a cathode compartment separated by a cation exchange membrane. Precipitation of phosphates from nanofiltration concentrate was induced by locally increasing the pH at the cathode surface by water electrolysis and thereby creating supersaturated conditions at the cathode. 70-95% recovery of total phosphate was achieved at a pH of 8-10 near the cathode. Ion analysis, XRD and ATR-FTIR spectra indicated that the precipitate consisted of amorphous calcium phosphate (ACP) and minor proportions of amorphous calcium carbonate (ACC). The amount of ACC was dependent on the pH. Calcium phosphate scaling at the cathode surface did not occur due to H 2-gas formation preventing nucleation and growth at the cathode. © 2013 Elsevier B.V. All rights reserved.
Dai, Y., Van Spronsen, J., Witkamp, G.-J., Verpoorte, R., Choi, Y.H.
Ionic liquids and deep eutectic solvents in natural products research: Mixtures of solids as extraction solvents
(2013) Journal of Natural Products, 76 (11), pp. 2162-2173.
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ABSTRACT: Mixtures of solid chemicals may become liquid under certain conditions. These liquids are characterized by the formation of strong ionic (ionic liquids) or hydrogen bonds (deep eutectic solvents). Due to their extremely low vapor pressure, they are now widely used in polymer chemistry and synthetic organic chemistry, yet little attention has been paid to their use as extraction solvents of natural products. This review summarizes the preparation of ionic liquids and deep eutectic solvents with natural product components and recent progress in their applications to the extraction and analysis of natural products as well as the recovery of extracted compounds from their extracts. Additionally, various factors affecting extraction features of ionic liquids and deep eutectic solvents, as well as potential useful technologies including microwave and ultrasound to increase the extraction efficiency, are discussed. © 2013 The American Chemical Society and American Society of Pharmacognosy.
Janssen, C.H.C., Sánchez, A., Witkamp, G.-J., Kobrak, M.N.
A novel mechanism for the extraction of metals from water to ionic liquids
(2013) ChemPhysChem, 14 (16), pp. 3806-3813.
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ABSTRACT: We present a novel mechanism for the extraction of metals from aqueous phases to room-temperature ionic liquids (ILs) by use of a high-temperature salt as an extraction agent. The mechanism capitalizes on the fact that charged metal complexes are soluble in ILs; this allows for extraction of charged complexes rather than the neutral species, which are formed by conventional approaches. The use of a well-chosen extraction agent also suppresses the competing ion-exchange mechanism, thus preventing degradation of the ionic liquid. The approach permits the use of excess extractant to drive the recovery of metals in high yield. This work presents both a thermodynamic framework for understanding the approach and experimental verification of the process in a range of different ILs. The method has great potential value in the recovery of metals, water purification and nuclear materials processing. Out of phase: A novel mechanism for the extraction of charged metal complexes from aqueous phases to ionic liquids is presented (see picture). The thermodynamics of the reaction are explored, and it is shown that the use of a suitable co-extraction agent can suppress the competing ion-exchange process. This method serves to drive the recovery of metals in high yield under relatively mild conditions. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Sutanto, S., van Roosmalen, M.J.E., Witkamp, G.J.
Mechanical action in CO2 dry cleaning
(2013) Journal of Supercritical Fluids, . Article in Press.
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ABSTRACT: High-pressure carbon dioxide (CO2) is a potential alternative for perchloroethylene (PER), a common but harmful textile dry cleaning solvent. Previous studies have indicated that the particulate soil removal with CO2 is lower compared to that with PER, because of the low amount of mechanical action in CO2. It is the objective of this study to get more insight in the influence of various types of mechanical action on the cleaning results in CO2 dry cleaning. In the experiments, various mechanisms of mechanical action, such as rotating drum, CO2 spray, and ultrasound were investigated. Several types of textiles stained with different kinds of particulate soils were cleaned using 25 L and 90 L CO2 dry cleaning set-ups. The washing results show that liquid CO2 spray may be a suitable additional mechanism to provide textile movement. The average CPI of CO2 over all soils using the best combination of commercial machine and process was still 25% lower than the results with PER and 18% lower than the results with water, but 11% higher than K4 solvent while the average redeposition level was significantly lower, showing that CO2 has a good prospect as an alternative solvent to replace PER. An endoscopic camera has been installed in the 25 L set-up to get an insight in the textile movement inside the rotating drum. The results show that no plug formation occurs and the textile movement in CO2 is sluggish, which means that the mechanical movement of textile in CO2 dry cleaning does not follow the simplified tumbling-movement model which was developed in a previous study, and the mechanical action is much less than predicted. © 2013 Elsevier B.V. All rights reserved.
Randall, D.G., Nathoo, J., Uner, F.E.G.G., Kramer, H.J.M., Witkamp, G.J., Lewis, A.E.
Erratum to "Determination of the metastable ice zone for a sodium sulphate system," [Chem. Eng. Sci. 77 (2012) 184-188]
(2013) Chemical Engineering Science, 101, p. 199.
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Rachmaniah, O., Choi, Y.H., Arruabarrena, I., Vermeulen, B., van Spronsen, J., Verpoorte, R., Witkamp, G.-J.
Environmentally benign supercritical CO2 extraction of galanthamine from floricultural crop waste of Narcissus pseudonarcissus
(2014) Journal of Supercritical Fluids, . Article in Press.
http://www.scopus.com/inward/record.url?eid=2-s2.0-84903319917&partnerID=40&md5=b9deed7d7f56157b2a06305471cd4e1b
ABSTRACT: The influence of diverse factors on the supercritical fluid extraction (SFE) with supercritical CO2 (scCO2) of galanthamine from bulbs of Narcissus pseudonarcissus cv. Carlton was investigated. The parameters that were studied were CO2 density (temperature and pressure), flow rate and plant material particle size and pre-treatment. The highest yield (303μg/g) was achieved by extracting 53-1000μm particle-size powdered dried bulb material moistened with NH4OH (25%, v/v) at 70°C, 220bar (690kg/m3) for 3h. Other N. pseudonarcissus alkaloids such as O-methyllycorenine and haemanthamine were also obtained. N. pseudonarcissus alkaloids as free bases are highly soluble in CO2 at a high pH as opposed to the slightly soluble salt form in which they are generally found in plants. Therefore, plant material pre-treatment with a base is an essential step for galanthamine extraction. Scanning electron microscope (SEM) results also revealed that the desorption of N. pseudonarcissus alkaloids from the plant material rather than the solubility of the alkaloids in the scCO2 plays a major role in this scCO2 extraction. This extraction method has a good potential for industrial application. © 2014 Elsevier B.V.
Sutanto, S., Van Roosmalen, M.J.E., Witkamp, G.J.
Redeposition in CO2 textile dry cleaning
(2013) Journal of Supercritical Fluids, 81, pp. 183-192.
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ABSTRACT: Perchloroethylene (PER) is commonly used as cleaning solvent in the textile dry-cleaning industry but this chemical is toxic by nature. One of the potential PER replacements is carbon dioxide (CO2), which is non-toxic, cheap, and widely available. Previous studies have indicated that the particulate soil removal with CO2 is lower compared to that of PER. While the particulate soil removal of the CO2 dry-cleaning was studied, it was found that redeposition of particulate soil occurs. Several experiments have been carried out to study and reduce this problem. In these experiments, textiles stained with different kinds of particulate soils were cleaned using a 25 L CO2 dry-cleaning set-up. It was found that the redeposition level increases along with washing time, while rinsing has little influence. Modifying the filtration system by using scavenger textile, or adding a cellulose compound to the cleaning vessel as anti redeposition agent can significantly reduce redeposition. © 2013 Elsevier B.V. All rights reserved.
Dai, Y., Witkamp, G.-J., Verpoorte, R., Choi, Y.H.
Natural deep eutectic solvents as a new extraction media for phenolic metabolites in carthamus tinctorius L.
(2013) Analytical Chemistry, 85 (13), pp. 6272-6278.
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ABSTRACT: Developing green solvents with low toxicity and cost is an important issue for the biochemical industry. Synthetic ionic liquids and deep eutectic solvents have received considerable attention due to their negligible volatility at room temperature, high solubilization ability, and tunable selectivity. However, the potential toxicity of the synthetic ionic liquids and the solid state at room temperature of most deep eutectic solvents hamper their application as extraction solvents. In this study, a wide range of recently discovered natural ionic liquids and deep eutectic solvents (NADES) composed of natural compounds were investigated for the extraction of phenolic compounds of diverse polarity. Safflower was selected as a case study because its aromatic pigments cover a wide range of polarities. Many advantageous features of NADES (such as their sustainability, biodegradability combined with acceptable pharmaceutical toxicity profiles, and their high solubilization power of both polar and nonpolar compounds) suggest their potential as green solvents for extraction. Experiments with different NADES and multivariate data analysis demonstrated that the extractability of both polar and less polar metabolites was greater with NADES than conventional solvents. The water content in NADES proved to have the biggest effect on the yield of phenolic compounds. Most major phenolic compounds were recovered from NADES with a yield between 75% and 97%. This study reveals the potential of NADES for applications involving the extraction of bioactive compounds from natural sources. © 2013 American Chemical Society.
Ogundiran, M.B., Nugteren, H.W., Witkamp, G.J.
Immobilisation of lead smelting slag within spent aluminate-fly ash based geopolymers
(2013) Journal of Hazardous Materials, 248-249 (1), pp. 29-36.
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ABSTRACT: This study presents the solidification/stabilisation and immobilisation of lead smelting slag (LSS) by its incorporation in coal fly ash - blast furnace slag based geopolymers. It also explores the use of a spent aluminium etching solution (AES) as geopolymer activator instead of the commonly used silicate solutions. The compressive strength of the geopolymers produced with the AES was lower than when applying a K-silicate solution as activator (100. MPa versus 80. MPa after 28 days). Compressive strength was not affected when up to 10% of the FA was replaced by LSS. NEN 12457-4, TCLP, SPLP and NEN 7375 leaching tests indicated that mobile Pb from LSS was highly immobilised. The diffusion leaching test NEN 7375 revealed exceeding of the Dutch Soil Quality Regulation threshold limits only for Se and Sb. On the condition that the remaining excess leaching can be reduced by further refinement of the mixture recipes, the proposed process will have the potential of producing waste-based construction materials that may be applied under controlled conditions in specific situations. © 2012 Elsevier B.V.
Dai, Y., van Spronsen, J., Witkamp, G.-J., Verpoorte, R., Choi, Y.H.
Natural deep eutectic solvents as new potential media for green technology
(2013) Analytica Chimica Acta, 766, pp. 61-68.
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ABSTRACT: Developing new green solvents is one of the key subjects in Green Chemistry. Ionic liquids (ILs) and deep eutectic solvents, thus, have been paid great attention to replace current harsh organic solvents and have been applied to many chemical processing such as extraction and synthesis. However, current ionic liquids and deep eutectic solvents have still limitations to be applied to a real chemical industry due to toxicity against human and environment and high cost of ILs and solid state of most deep eutectic solvents at room temperature. Recently we discovered that many plant abundant primary metabolites changed their state from solid to liquid when they were mixed in proper ratio. This finding made us hypothesize that natural deep eutectic solvents (NADES) play a role as alternative media to water in living organisms and tested a wide range of natural products, which resulted in discovery of over 100 NADES from nature. In order to prove deep eutectic feature the interaction between the molecules was investigated by nuclear magnetic resonance spectroscopy. All the tested NADES show clear hydrogen bonding between components. As next step physical properties of NADES such as water activity, density, viscosity, polarity and thermal properties were measured as well as the effect of water on the physical properties. In the last stage the novel NADES were applied to the solubilization of wide range of biomolecules such as non-water soluble bioactive natural products, gluten, starch, and DNA. In most cases the solubility of the biomolecules evaluated in this study was greatly higher than water. Based on the results the novel NADES may be expected as potential green solvents at room temperature in diverse fields of chemistry. © 2012 Elsevier B.V.
Salek, S.S., Kleerebezem, R., Jonkers, H.M., Witkamp, G.-J., Van Loosdrecht, M.C.M.
Mineral CO2 sequestration by environmental biotechnological processes
(2013) Trends in Biotechnology, 31 (3), pp. 139-146.
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ABSTRACT: CO2 sequestration may be an avenue to mitigate climate change. CO2 sequestration by mineral carbonation can be achieved by the reaction of CO2 with alkaline silicates. Here, we evaluate how alkaline silicate mineral-based CO2 sequestration can be achieved using environmental biotechnological processes. Several biotechnological processes rely on the sequence of (i) an acid-producing reaction such as nitrification and anaerobic fermentation and (ii) an alkalinity-producing reaction such as denitrification and methanogenesis. Whereas the acid-producing reaction can be used to enhance the dissolution of, for example, alkaline calcium silicates, the subsequent alkalinity-producing step can precipitate CaCO3. We quantitatively evaluate the potential of these processes for CO2 sequestration and propose that optimization of these processes could contribute to climate change mitigation strategies. © 2013 Elsevier Ltd.
Salvador Cob, S., Beaupin, C., Hofs, B., Nederlof, M.M., Harmsen, D.J.H., Cornelissen, E.R., Zwijnenburg, A., Genceli Güner, F.E., Witkamp, G.J.
Amorphous aluminosilicate scaling characterization in a reverse osmosis membrane
(2013) Desalination and Water Treatment, 51 (4-6), pp. 936-943.
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ABSTRACT: This paper describes the results of experiments performed in a high-recovery system to elucidate the silica scaling phenomenon and characterize the scaling. In this research, cation exchange pretreatment is used to reduce Ca2+, Ba2+, and Mg2+ levels to prevent scaling during subsequent nanofiltration (NF) and reverse osmosis (RO) filtration, in which RO is fed with NF concentrate. In a pilot plant, a series of experiments were carried out at a total (NF + RO) recovery of 91, 94, 96 and 98% with locally available tap water as feed water. Autopsy studies were performed with the RO membranes after each experiment. The fouling layer was studied using SEM-EDX, ATR-FTIR and fouling extraction to determine the structure and the composition of the fouling deposits. A thin dense fouling layer was observed, which covered approximately half of the membrane surface, after operating for 20 days at 91 and 94% recovery. At 96 and 98% recovery, the fouling layer was thicker and completely covered the membrane surface. The scaling layer was mainly composed of Si, Al, Fe and O. The amount of Si increased with increasing recovery. To work at these high recoveries for an extended period, further measures need to be taken to prevent silica scaling. © 2013 Desalination Publications.
Salvador Cob, S., Beaupin, C., Hofs, B., Nederlof, M.M., Harmsen, D.J.H., Cornelissen, E.R., Zwijnenburg, A., Genceli Güner, F.E., Witkamp, G.J.
Silica and silicate precipitation as limiting factors in high-recovery reverse osmosis operations
(2012) Journal of Membrane Science, 423-424, pp. 1-10.
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ABSTRACT: This paper investigated silica and silicate precipitation as limiting factors in high-recovery membrane operations. For this purpose a cation exchange pretreatment is proposed to reduce Ca 2+, Ba 2+, Mg 2+ levels to prevent scaling of salts containing these ions during subsequent NF and RO filtration, in which RO is fed with NF concentrate. In a pilot plant experiments were carried out at total (NF+RO) water recovery of 91, 94, 96 and 98% with locally available tap water which contains 20mg/L of silica as feed water. Autopsy studies were performed with the RO membranes after each experiment in which the fouling layer was studied using SEM-EDX to determine the structure and the composition of the fouling deposits. A thin cake layer was observed which covered approximately half of the membrane surface after operating for 20 days at 91 and 94% recovery. At 96 and 98% recovery the fouling layer was thicker and completely covered the membrane surface. EDX analysis indicated that the fouling layer was mainly composed of Si, Al, Fe and O, most likely due to the presence of iron oxides, iron hydroxides, silica and aluminosilicates. To be able to work at these high recoveries for an extended period, further measures need to be taken to prevent silica and aluminosilicate scaling. © 2012 Elsevier B.V.
Wagterveld, R.M., Miedema, H., Witkamp, G.-J.
Effect of ultrasonic treatment on early growth during CaCO 3 precipitation
(2012) Crystal Growth and Design, 12 (9), pp. 4403-4410.
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ABSTRACT: The present study focuses on the effect of ultrasound (42 kHz, 7.1 W cm -2) on the free drift precipitation of CaCO 3 from a clear, supersaturated solution. To delineate the way ultrasound exerts its effect, we applied different treatment periods (time windows). Applying ultrasound during the first 10 min of the experiment did not result in any significant effect which rules out an influence on primary nucleation. The application of ultrasound starting later in the experiment enhanced precipitation of CaCO 3. The dominant mechanism responsible for enhanced precipitation is deaggregation during the early growth phase (nuclei to crystals conversion regime). This effect is attributed to shear induced by micromixing and/or shear/stress induced by (supersonic) shockwaves, as a result of cavitation. With ultrasound applied, online pH and scattering measurements displayed a reduction in induction time and an increase in the volumetric precipitation rate. Scanning electron microscopy analysis shows that ultrasound increases the total number of particles that has, in addition, a more uniform size distribution compared with the untreated experiment. Consequently the available surface area for growth is higher resulting in a higher volumetric precipitation rate. With and without ultrasound the formed polymorph was predominantly vaterite with small amounts of calcite. © 2012 American Chemical Society.
Boels, L., Keesman, K.J., Witkamp, G.-J.
Adsorption of phosphonate antiscalant from reverse osmosis membrane concentrate onto granular ferric hydroxide
(2012) Environmental Science and Technology, 46 (17), pp. 9638-9645.
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ABSTRACT: Adsorptive removal of antiscalants offers a promising way to improve current reverse osmosis (RO) concentrate treatment processes and enables the reuse of the antiscalant in the RO desalination process. This work investigates the adsorption and desorption of the phosphonate antiscalant nitrilotris(methylenephosphonic acid) (NTMP) from RO membrane concentrate onto granular ferric hydroxide (GFH), a material that consists predominantly of akaganéite. The kinetics of the adsorption of NTMP onto GFH was predicted fairly well with two models that consider either combined film-pore or combined film-surface diffusion as the main mechanism for mass transport. It is also demonstrated that NTMP is preferentially adsorbed over sulfate by GFH at pH 7.85. The presence of calcium causes a transformation in the equilibrium adsorption isotherm from a Langmuir type to a Freundlich type with much higher adsorption capacities. Furthermore, calcium also increases the rate of adsorption substantially. GFH is reusable after regeneration with sodium hydroxide solution, indicating that NTMP can be potentially recovered from the RO concentrate. This work shows that GFH is a promising adsorbent for the removal and recovery of NTMP antiscalant from RO membrane concentrates. © 2012 American Chemical Society.
Randall, D.G., Nathoo, J., Genceli-Güner, F.E., Kramer, H.J.M., Witkamp, G.J., Lewis, A.E.
Determination of the metastable ice zone for a sodium sulphate system
(2012) Chemical Engineering Science, 77, pp. 184-188.
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ABSTRACT: The crystallisation of ice from a 1. wt% sodium sulphate solution was investigated at different cooling rates and solution volumes in order to determine the metastable zone (MSZ) for the system. The results from this study showed that there was a large variation in nucleation temperatures, thus confirming the stochastic nature of nucleation. The results also showed that the width of the MSZ was independent of solution volumes greater than 250. mL. The nucleation temperatures for smaller solution volumes showed a greater spread than the larger solution volumes. The smallest MSZW for a 1. wt% sodium sulphate solution (1.8. mL volume) was 2.6 °C for a cooling rate of 2 °C/h, 2.8 °C for a cooling rate of 4 °C/h and 4.8 °C for a cooling rate of 8 °C/h. © 2011 Elsevier Ltd.
Banerjee, S., Sutanto, S., Kleijn, J.M., Van Roosmalen, M.J.E., Witkamp, G.-J., Stuart, M.A.C.
Colloidal interactions in liquid CO 2 - A dry-cleaning perspective
(2012) Advances in Colloid and Interface Science, 175, pp. 11-24.
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ABSTRACT: Liquid CO 2 is a viable alternative for the toxic and environmentally harmful solvents traditionally used in dry-cleaning industry. Although liquid CO 2 dry-cleaning is being applied already at a commercial scale, it is still a relatively young technique which poses many challenges. The focus of this review is on the causes of the existing problems and directions to solve them. After presenting an overview of the state-of-the-art, we analyze the detergency challenges from the fundamentals of colloid and interface science. The properties of liquid CO 2 such as dielectric constant, density, Hamaker constant, refractive index, viscosity and surface tension are presented and in the subsequent chapters their effects on CO 2 dry-cleaning operation are delineated. We show, based on theory, that the van der Waals forces between a model soil (silica) and model fabric (cellulose) through liquid CO 2 are much stronger compared to those across water or the traditional dry-cleaning solvent PERC (perchloroethylene). Prevention of soil particle redeposition in liquid CO 2 by electrostatic stabilization is challenging and the possibility of using electrolytes having large anionic parts is discussed. Furthermore, the role of different additives used in dry-cleaning, such as water, alcohol and surfactants, is reviewed. Water is not only used as an aid to remove polar soils, but also enhances adhesion between fabric and soil by forming capillary bridges. Its role as a minor component in liquid CO 2 is complex as it depends on many factors, such as the chemical nature of fabrics and soil, and also on the state of water itself, whether present as molecular solution in liquid CO 2 or phase separated droplets. The phenomena of wicking and wetting in liquid CO 2 systems are predicted from the Washburn-Lucas equation for fabrics of various surface energies and pore sizes. It is shown that nearly complete wetting is desirable for good detergency. The effect of mechanical action and fluid dynamic conditions on dry-cleaning is analyzed theoretically. From this it follows that in liquid CO 2 an order of magnitude higher Reynold's number is required to exceed the binding forces between fabric and soil as opposed to PERC or water, mainly due to the strong van der Waals forces and the low viscosity of CO 2 at dry-cleaning operational conditions. © 2012 Elsevier B.V.
Waly, T., Kennedy, M.D., Witkamp, G.-J., Amy, G., Schippers, J.C.
The role of inorganic ions in the calcium carbonate scaling of seawater reverse osmosis systems
(2012) Desalination, 284, pp. 279-287.
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ABSTRACT: In supersaturated solutions the period preceding the start of 'measurable' crystallization is normally referred to as the 'induction time'. This research project aimed to investigate the induction times of CaCO 3 in the presence of Mg 2+ and SO 4 2-. The prepared synthetic solutions have the same ionic strength values found in the Gulf of Oman SWRO concentrates at 30% and 50% recovery. The results showed a significant increase in the induction time by 1140%, 2820%, and 3880% for a recovery of 50%, when adding SO 4 2- only, Mg 2+ only, or both Mg 2+ and SO 4 2-, respectively, to synthetic SWRO concentrate compared to that obtained in the absence of Mg 2+ and SO 4 2- at an initial pH of 8.3. The increase in the induction time in the presence of SO 4 2- was more than likely to be due to nucleation and growth inhibition while the presence of Mg 2+ affected the nucleation and growth through both complexation and inhibition. After a 5-month solution stabilization period, ESEM and XRD analyses showed aragonite in solutions containing Mg 2+. On the contrary, calcite was the final crystal phase formed in solutions with no Mg 2+. This suggests that magnesium may play an important role in inhibiting the formation of calcite. © 2011 Elsevier B.V..
Waly, T., Kennedy, M.D., Witkamp, G.-J., Amy, G., Schippers, J.C.
On the induction time of CaCO3: Effect of ionic strength
(2012) Desalination and Water Treatment, 39 (1-3), pp. 55-69.
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ABSTRACT: This research investigated the induction times of CaCO3 as a function of the saturation and ionic strength for synthetic solutions based on the Gulf of Oman seawater analysis. The investigation aimed to determine at elevated ionic strength levels, (i) the CaCO3 phase incorporated in the Stiff and Davis saturation index and (ii) the mechanism of nucleation involved. Induction time experiments were performed with synthetic concentrates having different ionic strengths of 0.054, 1.12, 1.34, 1.61 mole/l. Results showed that S&DSI incorporate the solubility of calcite at low ionic strength but vaterite for high ionic strength water. This expectation was confirmed with microscopic analysis of the formed crystals at the end of the induction time experiments (24 h) as vaterite was found in the solution instead of calcite. These findings indicate that vaterite and not calcite maybe the precipitating phase in seawater. The study of the mechanism of nucleation showed three different trends describing three different nucleation mechanisms; namely homogenous, heterogeneous and a one characterized by an intermediate surface tension. The calculations of the apparent surface energy showed values ranging from 15-94 mJ/m2 which is consistent with literature data for vaterite. Results suggest that for the level of saturation reached in SWRO systems, the nucleation mechanism will most probably be heterogeneous. © 2012 Desalination Publications.
Waly, T., Kennedy, M.D., Witkamp, G.-J., Amy, G., Schippers, J.C.
Predicting and measurement of pH of seawater reverse osmosis concentrates
(2011) Desalination, 280 (1-3), pp. 27-32.
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ABSTRACT: The pH of seawater reverse osmosis plants (SWRO) is the most influential parameter in determining the degree of supersaturation of CaCO3 in the concentrate stream. For this, the results of pH measurements of the concentrate of a seawater reverse osmosis pilot plant were compared with pH calculations based on the CO2-HCO3 --CO3 2- system equilibrium equations. Results were compared with two commercial software programs from membrane suppliers and also the software package Phreeqc. Results suggest that the real concentrate pH is lower than that of the feed and that none of the used programs was able to predict correctly real pH values. In addition, the effect of incorporating the acidity constant calculated for NaCl medium or seawater medium showed a great influence on the concentrate pH determination. The HCO3 - and CO3 2- equilibrium equation using acidity constants developed for seawater medium was the only method able to predict correctly the concentrate pH. The outcome of this study indicated that the saturation level of the concentrate was lower than previously anticipated. This was confirmed by shutting down the acid and the antiscalants dosing without any signs of scaling over a period of 12 months. © 2011 Elsevier B.V.
Boels, L., Witkamp, G.-J.
Carboxymethyl inulin biopolymers: A green alternative for phosphonate calcium carbonate growth inhibitors
(2011) Crystal Growth and Design, 11 (9), pp. 4155-4165.
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ABSTRACT: There is a growing demand for environmentally friendly alternatives for phosphonate-based crystal growth inhibitors (or antiscalants) used in reverse osmosis desalination, which are nontoxic, biodegradable, and free of phosphorus. The effectiveness of such an alternative, carboxymethyl inulin (CMI) biopolymers, in inhibiting calcium carbonate crystallization (CaCO3) was compared to that of nitrilotris(methylenephosphonic acid) (NTMP) and 1-hydroxyethane-1,1-diphosphonate (HEDP). Their inhibiting effect on the seeded growth of calcite was investigated using the constant composition method at different solution compositions. The values of inhibited growth rates could be related well to a Temkin adsorption isotherm. Compared to HEDP and NTMP, CMI-20 and CMI-25 biopolymers exhibited an equally stronger inhibitory effect on the seeded growth of calcite, despite their different degrees of carboxylation. The ability of the inhibitor molecules to mitigate the spontaneous precipitation of CaCO3 in a synthetic membrane concentrate was investigated as well. The results show that the ability of the biopolymers to mitigate precipitation is controlled by their degree of carboxylation. About 2.7 times more NTMP than CMI-25 is needed to achieve a similar precipitation inhibition. At high concentrations, both NTMP and CMI-25 induced twinning in the precipitating calcite crystals. This demonstrates that CMI biopolymers are effective CaCO 3 growth inhibitors, indicating their potential as a green alternative for phosphonates. © 2011 American Chemical Society.
Boels, L., Wagterveld, R.M., Witkamp, G.J.
Ultrasonic reactivation of phosphonate poisoned calcite during crystal growth
(2011) Ultrasonics Sonochemistry, 18 (5), pp. 1225-1231.
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ABSTRACT: The effect of ultrasonic irradiation (42,150 Hz, 17 W dm-3/7.1 W cm-2) on the growth of calcite in the presence of the inhibitor nitrilotris(methylene phosphonic acid) (NTMP) was investigated at constant composition conditions. In seeded growth experiments, it was found that the inhibiting effect of NTMP on crystal growth could be seriously mitigated under influence of ultrasonic irradiation. An approximately twofold increase in volumetric growth rate was achieved during ultrasonic irradiation, and recovery of the growth rate following inhibition was strongly enhanced compared to growth experiments without ultrasonic irradiation. The results could be explained in part by the physical effect of ultrasound that causes breakage and attrition of poisoned crystals, which resulted in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that there is also a chemical effect of ultrasound that plays an important role. Several breakdown products were identified, which showed that ultrasound caused the progressive loss of phosphonate groups from NTMP, probably by means of physicochemically generated free radicals and/or pyrolysis in the hot bubble-bulk interface. © 2011 Elsevier B.V. All rights reserved.
Choi, Y.H., van Spronsen, J., Dai, Y., Verberne, M., Hollmann, F., Arends, I.W.C.E., Witkamp, G.-J., Verpoorte, R.
Are natural deep eutectic solvents the missing link in understanding cellular metabolism and physiology?
(2011) Plant Physiology, 156 (4), pp. 1701-1705.
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Perrotin-Brunel, H., Buijs, W., Spronsen, J.V., Roosmalen, M.J.E.V., Peters, C.J., Verpoorte, R., Witkamp, G.-J.
Decarboxylation of Δ9-tetrahydrocannabinol: Kinetics and molecular modeling
(2011) Journal of Molecular Structure, 987 (1-3), pp. 67-73.
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ABSTRACT: Efficient tetrahydrocannabinol (Δ9-THC) production from cannabis is important for its medical application and as basis for the development of production routes of other drugs from plants. This work presents one of the steps of Δ9-THC production from cannabis plant material, the decarboxylation reaction, transforming the Δ9- THC-acid naturally present in the plant into the psychoactive Δ9-THC. Results of experiments showed pseudo-first order reaction kinetics, with an activation barrier of 85 kJ mol-1 and a pre-exponential factor of 3.7 × 108 s-1. Using molecular modeling, two options were identified for an acid catalyzed β-keto acid type mechanism for the decarboxylation of Δ9- THC-acid. Each of these mechanisms might play a role, depending on the actual process conditions. Formic acid proved to be a good model for a catalyst of such a reaction. Also, the computational idea of catalysis by water to catalysis by an acid, put forward by Li and Brill, and Churchev and Belbruno was extended, and a new direct keto-enol route was found. A direct keto-enol mechanism catalyzed by formic acid seems to be the best explanation for the observed activation barrier and the pre-exponential factor of the decarboxylation of Δ9-THC-acid. Evidence for this was found by performing an extraction experiment with Cannabis Flos. It revealed the presence of short chain carboxylic acids supporting this hypothesis. The presented approach is important for the development of a sustainable production of Δ9-THC from the plant. © 2010 Elsevier B.V. All rights reserved.
van Spronsen, J., Cardoso, M.A.T., Witkamp, G.-J., de Jong, W., Kroon, M.C.
Separation and recovery of the constituents from lignocellulosic biomass by using ionic liquids and acetic acid as co-solvents for mild hydrolysis
(2011) Chemical Engineering and Processing: Process Intensification, 50 (2), pp. 196-199.
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ABSTRACT: Previously, ionic liquids were found to partially dissolve lignocellulosic biomass. Here, it is reported that the biomass itself does not dissolve directly, but that it is hydrolyzed first before the constituents (cellulose, hemicellulose and lignin) dissolve into the ionic liquid. By addition of an acidic catalyst, this hydrolysis step can take place at milder conditions. Acetic acid is chosen as a suitable acidic catalyst, because it is already present in lignocellulosic biomass in the form of acetyl groups on the hemicellulose. Here, it is shown that acetic acid also works as co-solvent, increasing the solubility of the constituents of lignocellulosic biomass in the ionic liquid. The milder conditions for hydrolysis result in a higher degree of utilization of the lignocellulosic biomass, whereby all constituents can be fully recovered and further processed and the ionic liquid can be reused. © 2010 Elsevier B.V.
Wagterveld, R.M., Boels, L., Mayer, M.J., Witkamp, G.J.
Visualization of acoustic cavitation effects on suspended calcite crystals
(2011) Ultrasonics Sonochemistry, 18 (1), pp. 216-225.
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ABSTRACT: The acoustic cavitation (42,080Hz, 7.1Wcm-2 or 17W) effects on suspended calcite crystals, sized between 5 and 50μm, have been visualized for the first time using high speed photography. High speed recordings with a duration of 1s containing up to 300,000 frames per second, revealed the effect of cluster and streamer cavitation on several calcite crystals. Cavitation clusters, evolved from cavitation inception and collapse, caused attrition, disruption of aggregates and deagglomeration, whereas streamer cavitation was observed to cause deagglomeration only. Cavitation on the surface gave the crystals momentum. However, it is shown that breakage of accelerated crystals by interparticle collisions is unrealistic because of their small sizes and low velocities. Crystals that were accelerated by bubble expansion, subsequently experienced a deceleration much stronger than expected from drag forces, upon bubble collapse. Experiments with pre-dried crystals seemed to support the current theory on bubble nucleation through the presence of pre-existing gas pockets. However, experiments with fully wetted crystals also showed the nucleation of bubbles on the crystal surface. Although microjet impingement on the crystal surface could not be directly visualized with high speed photography, scanning electron microscopy (SEM) analysis of irradiated calcite seeds showed deep circular indentations. It was suggested that these indentations might be caused by shockwave induced jet impingement. Furthermore, the appearance of voluminous fragments with large planes of fracture indicated that acoustic cavitation can also cause the breakage of single crystal structures. © 2010 Elsevier B.V.
Mulia, K., Witkamp, G.-J., Dawes, G.J.S., Fratila-Apachitei, L.E., Apachitei, I., Duszczyk, J., Pellikaan, H.
Drug release from PLGA microspheres attached to solids using supercritical CO2
(2011) Journal of Biomaterials Applications, 25 (5), pp. 401-412.
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ABSTRACT: Functionalization of a porous orthopedic implant with dexamethasone, a widely used anti-inflammatory drug, encapsulated within a biodegradable polymer for controlled release could help reduce or eliminate the inflammation response by the local tissue. In this research, we investigated the possibility of using supercritical carbon dioxide (CO2) for attaching dexamethasone-loaded PLGA (polylactic-co-glycolic acid) microspheres to porous CoCrMo alloy for continuous delivery of dexamethasone. Supercritical CO2 has been shown to be effective for attachment of PLGA microspheres to glass plates and porous CoCrMo alloy. Attached microspheres showed similar dexamethasone release profiles but different magnitude of burst release. Microspheres attached to the porous alloy samples using supercritical CO2 at 10 bar and 40°C for 30 min showed a release profile similar to that of the nonattached microspheres. The microsphere morphology and the release profiles of microspheres attached to the glass plates and to the porous alloy samples suggest that dexamethasone burst release is enhanced by PLGA swelling at higher CO2 pressures and better dispersion of microspheres. This study shows that microspheres can be incorporated into porous solids using supercritical CO2, allowing for a wide variety of drug-biodegradable polymer formulations prepared using the proven emulsion/solvent evaporation method to be tested. © 2011 The Author(s).
Perrotin-Brunel, H., Kroon, M.C., Van Roosmalen, M.J.E., Van Spronsen, J., Peters, C.J., Witkamp, G.-J.
Solubility of non-psychoactive cannabinoids in supercritical carbon dioxide and comparison with psychoactive cannabinoids
(2010) Journal of Supercritical Fluids, 55 (2), pp. 603-608.
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ABSTRACT: The solubilities of two different non-psychoactive cannabinoids i.e., cannabigerol (CBG) and cannabidiol (CBD), in supercritical carbon dioxide (CO2) have been determined at 315, 326 and 334 K and in the pressure range from 11.3 to 20.6 MPa. These solubility data have been compared to the previously determined solubilities of two psychoactive cannabinoids i.e., (-)-Δ9-tetrahydrocannabinol (Δ9-THC) and cannabinol (CBN), in supercritical CO2. An analytical method with a quasi-flow apparatus was used for the experimental determination. Within the investigated temperature and pressure range, the molar solubility of CBG ranged from 1.17 to 1.91 × 10-4 and the molar solubility of CBD ranged from 0.88 to 2.69 × 10-4. The solubility of the different cannabinoids in supercritical CO2 increases at 326 K in the following order: Δ9-THC < CBG < CBD < CBN. The solubility data were correlated using the Peng-Robinson equation of state in combination with Van der Waals mixing rules. Deviations between calculated results and the experimental data ranged from 0.81 to 6.35% absolute average relative deviation (AARD), except for CBD at 334 K, where the AARD was 18.4%. © 2010 Elsevier B.V. © 2010 Elsevier B.V. All rights reserved.
Boels, L., Tervahauta, T., Witkamp, G.J.
Adsorptive removal of nitrilotris(methylenephosphonic acid) antiscalant from membrane concentrates by iron-coated waste filtration sand
(2010) Journal of Hazardous Materials, 182 (1-3), pp. 855-862.
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ABSTRACT: Iron-coated waste filtration sand was investigated as a low-cost adsorbent for the removal of nitrilotris(methylenephosphonic acid) (NTMP) from membrane concentrates. The adsorption of this phosphonate-based antiscalant on this material was measured and compared with two commercially available anion exchange resins and activated carbon. Comprehensive adsorption experiments were conducted in several synthetic concentrate solutions and in a concentrate collected from a full scale nano-filtration brackish water desalination plant. The effect of pH, ionic strength and the presence of competitive anions on the equilibrium adsorption were investigated. The results showed that, in contrast to the anion exchange resins, the adsorption on coated filtration sand is not suppressed at increasing ionic strength and is much less affected by the competitive anions carbonate and sulphate. The adsorption decreased slightly when the pH was raised from 7.0 to 8.0. The adsorption isotherms in the real nano-filtration concentrate, measured in the concentration interval of 5-50mgdm-1 NTMP, showed that the maximum adsorption capacity of coated filtration sand was 4.06mgg-1. The adsorption capacity per unit mass of the adsorbents at low NTMP concentration (12.5mgdm-3) followed the decreasing order Amberlite IRA-410>coated filtration sand>Amberlite IRA-900>Norit SAE Super. This demonstrates that the use of iron-coated waste filtration sand offers a promising means for the removal of NTMP from membrane concentrates. © 2010 Elsevier B.V.
Pascual, M.R., Trambitas, D., Calvo, E.S., Kramer, H., Witkamp, G.-J.
Determination of the eutectic solubility lines of the ternary system NaHCO3-Na2CO3-H2O
(2010) Chemical Engineering Research and Design, 88 (10), pp. 1365-1371.
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ABSTRACT: A crystallizer was built and a procedure developed to accurately measure the eutectic solubility lines where ice and salt coexist in equilibrium with the solution, for potential application of Eutectic Freeze Crystallization. The eutectic solubility lines of the ternary system NaHCO3-Na2CO3-H2O were determined experimentally and calculated with the extended UNIQUAC model. The extended UNIQUAC model describes the experimental data quite well. Anhydrous NaHCO3 and Na2CO3·10H2O were the only two types of crystals present in equilibrium with ice crystals in the ternary system. At the quadruple point NaHCO3 and Na2CO3·10H2O are in equilibrium with a solution of about 4.34wt% of Na2CO3 and 4.77wt% of NaHCO3 at -3.32°C. The anhydrous NaHCO3 crystals were needle shaped with lengths between 5 and 10μm, that were agglomerated into particles of about 100-300μm, while the Na2CO3·10H2O crystals were hexagonally shaped with sizes between 100 and 500μm. © 2009 The Institution of Chemical Engineers.
Perrotin-Brunel, H., Van Roosmalen, M.J.E., Kroon, M.C., Van Spronsen, J., Witkamp, G.-J., Peters, C.J.
Solubility of cannabinol in supercritical carbon dioxide
(2010) Journal of Chemical and Engineering Data, 55 (9), pp. 3704-3707.
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ABSTRACT: Cannabinol (CBN) is a decomposition product of the cannabinoid (-)-Δ9-tetrahydrocannabinol (Δ9-THC), the main active compound of cannabis. The solubility of CBN in supercritical carbon dioxide was determined at (314, 327, and 334) K and in the pressure range from (13.0 to 20.2) MPa by using an analytical method with a quasi-flow apparatus. The molar solubility of CBN ranged from 1.26·10-4 to 4.16·10-4. CBN showed different behavior compared to Δ9-THC in terms of molar solubility. The data were correlated using the Peng-Robinson equation of state in combination with quadratic mixing rules. Deviations between calculated results and the experimental data ranged from (4.14 to 4.46) % absolute average relative deviation (AARD). © 2010 American Chemical Society.
Janssen, C.H.C., Kroon, M.C., Metz, S.J., Van Spronsen, J., Witkamp, G.-J.
Extraction of sodium chloride from water and solubility of water in hydrophobic trialkylammonium alkanoate-based ionic liquids
(2010) Journal of Chemical and Engineering Data, 55 (9), pp. 3391-3394.
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ABSTRACT: The sodium chloride extraction from aqueous solutions by using hydrophobic trialkylammonium alkanoate ionic liquids (ILs) is studied experimentally. The water solubility in these ILs is also determined. It is found that trialkylammonium alkanoate ILs show sodium chloride extraction efficiencies up to 0.101 g NaCl extracted/g NaCl start. This efficiency cannot be explained by the low water uptake (up to 0.02 gwater/gIL) in the IL. Instead, the sodium chloride extraction must be attributed to other factors, such as steric hindrance considerations. Steric hindrance considerations also explain the dependence of sodium chloride extraction efficiency on the IL structure. Kinetic experiments were performed to ensure a state of chemical equilibrium. © 2010 American Chemical Society.
Lewis, A.E., Nathoo, J., Thomsen, K., Kramer, H.J., Witkamp, G.J., Reddy, S.T., Randall, D.G.
Design of a Eutectic Freeze Crystallization process for multicomponent waste water stream
(2010) Chemical Engineering Research and Design, 88 (9), pp. 1290-1296.
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ABSTRACT: Complex, hypersaline brines originating from the mining and extractive metallurgical industries have the potential to be treated using Eutectic Freeze Crystallization (EFC). Although EFC has been shown to be effective in separating a single salt and water, it has yet to be applied to the complex hypersaline brines that are typical of reverse osmosis retentates in South Africa. This paper focuses on the application of EFC for the purification of a typical brine containing high levels of sodium, chlorine, sulphate and ammonia that cannot be achieved with other separation techniques. The presence of ammonia prevents the application of membrane technology to treat the brine, leaving only cooling or evaporation as other possible options. Evaporation produces a mixed salt that requires further treatment. Modelling tools were applied to describe the phase behaviour of the complex saline systems under different process conditions and were experimentally validated. The results showed that Eutectic Freeze Crystallization could be used to selectively recover the sodium as a sodium sulphate salt. The simulation tools were especially useful in the design and optimisation of the process. © 2010 The Institution of Chemical Engineers.
Reddy, S.T., Lewis, A.E., Witkamp, G.J., Kramer, H.J.M., van Spronsen, J.
Recovery of Na2SO4·10H2O from a reverse osmosis retentate by eutectic freeze crystallisation technology
(2010) Chemical Engineering Research and Design, 88 (9), pp. 1153-1157.
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ABSTRACT: The increasing amount of waste water and effluent from South Africa's mining industry forms a growing problem, which processing requires sustainable solutions in which both the water and the dissolved component can be re-used. Eutectic freeze crystallisation (EFC) has been identified as a key technology that is not only energy efficient, but also produces ice and salt products of high quality. Unlike reverse osmosis membrane systems, EFC can treat both dilute and concentrated systems minimising waste water volumes. In this paper it is shown that freeze and eutectic freeze crystallisation can be used for the processing of a reverse osmosis retentate stream containing 4% NaSO4 and a number of impurities (F, Cl, K, Li, Mg, Ca, NO3 and NH4), producing both pure water and NaSO4·10H2O crystals. The influence of the impurities on the eutectic point and on the crystal structure of mirabilite was investigated using EFC technology investigated for a pure binary system, for a synthetic reverse osmosis retentate as well as for a concentrated NaCl system. In addition, investigations into the recovery and purity of mirabilite for these streams were conducted. © 2010 The Institution of Chemical Engineers.
Rodriguez Pascual, M., Genceli, F.E., Trambitas, D.O., Evers, H., Van Spronsen, J., Witkamp, G.J.
A novel scraped cooled wall crystallizer. Recovery of sodium carbonate and ice from an industrial aqueous solution by eutectic freeze crystallization
(2010) Chemical Engineering Research and Design, 88 (9), pp. 1252-1258.
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ABSTRACT: A novel scraped cooled wall crystallizer (SCWC-2) with 130l capacity and total heat transfer area of 2.94m2m-3 crystallizer volume was specifically designed for eutectic freeze crystallization (EFC). It has been successfully tested for the recovery of Na2CO3 from an industrial solution. Compared with earlier designs this new crystallizer shows a high improvement in gravitational separation and ice scaling removal. High heat transfer fluxes between the heat exchanger and the solution (up to 10.5kWm-2) were obtained and as a consequence high production rates were achieved. © 2009.
Van Spronsen, J., Pascual, M.R., Genceli, F.E., Trambitas, D.O., Evers, H., Witkamp, G.J.
Eutectic freeze crystallization from the ternary Na2CO3-NaHCO3-H2O system. A novel scraped wall crystallizer for the recovery of soda from an industrial aqueous stream
(2010) Chemical Engineering Research and Design, 88 (9), pp. 1259-1263.
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ABSTRACT: Eutectic freeze crystallization was tested in a scaled up version of a scraped cooled wall crystallizer on an industrial aqueous sodium carbonate-sodium bicarbonate waste stream containing traces of molybdenum. A heat transfer rate of 5kWm-2 was maintained in the crystallizer. Sodium carbonate decahydrate with molybdenum content below 1ppm and pure ice were produced by continuous crystallization at -3.8°C by operating within the metastable zone width of bicarbonate. At -4.0°C bicarbonate started to co-crystallize. The bimodal size distribution of the mixture resulted in poor filtration and purity of the salt product. © 2009 The Institution of Chemical Engineers.
Kroon, M.C., Florusse, L.J., Kühne, E., Witkamp, G.-J., Peters, C.J.
Achievement of a homogeneous phase in ternary ionic liquid/carbon dioxide/organic systems
(2010) Industrial and Engineering Chemistry Research, 49 (7), pp. 3474-3478.
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ABSTRACT: A few years ago, it was found that carbon dioxide (CO2) is able to induce in ternary ionic liquid (IL) + organic systems, a "two-phase (L + V)-three-phase (L1 + L2 + V)-two-phase (L1 + L2)" transition by pressure increase. In the two liquid phase region (L1 + L2), one of the phases did not contain any IL. Therefore, the organic compound could be separated from the IL at increased CO2 pressure without any IL contamination. However, the occurrence of a homogeneous phase by further pressure increase, a so-called L1 + L2 f L transition, in the same systems was never observed before. Here, we demonstrate that in addition a third phase transition is possible upon further CO2 pressure increase, where the two liquid phases (L 1 + L2) can be forced to form one homogeneous liquid phase (L). This phenomenon has promising implications for reactions and separations in systems using ILs. © 2010 American Chemical Society.
Sabil, K.M., Witkamp, G.-J., Peters, C.J.
Estimations of enthalpies of dissociation of simple and mixed carbon dioxide hydrates from phase equilibrium data
(2010) Fluid Phase Equilibria, 290 (1-2), pp. 109-114.
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ABSTRACT: In the present work, the stability conditions of simple and mixed carbon dioxide (CO2) and tetrahydrofuran (THF) hydrates are experimentally measured. Considering the difficulties of obtaining the enthalpy of dissociation data through direct measurements, the enthalpies of dissociation for these hydrates are estimated from the measured equilibrium data by applying the Clausius-Clapeyron equation. The results of the calculated enthalpy of dissociation for simple CO2 and mixed CO2 and THF hydrates are presented and discussed. It is found that the estimated enthalpy of dissociation of simple CO2 hydrate varied from 56.85 to 75.37 kJ/mol, as the temperature is reduced from 282.06 to 273.15 K. Depending on the concentration of carbon dioxide and tetrahydrofuran in the hydrate forming systems, the enthalpy of dissociation of mixed carbon dioxide and tetrahydrofuran is found to be in the region of 112.37-152.27 kJ/mol. A rationale for this significant increase of the enthalpy of dissociation of the mixed hydrates is discussed. © 2009 Elsevier B.V. All rights reserved.
Boels, L., Wagterveld, R.M., Mayer, M.J., Witkamp, G.J.
Seeded calcite sonocrystallization
(2010) Journal of Crystal Growth, 312 (7), pp. 961-966.
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ABSTRACT: The seeded sonocrystallization of calcite was investigated by measuring the volumetric crystallization rate at constant composition conditions. The crystallization rate of calcite was enhanced by 46% through ultrasonic irradiation (42,150 Hz, 17 W dm-3) of a supersaturated crystal suspension. It was shown that this effect was related to the alteration of the seed crystals' habit and size. During ultrasonic irradiation disruption of conglomerates and erosion of single crystals occurred, accompanied by the production of many fines. The increased surface area available for crystal growth resulted in the observed crystallization rate enhancement. © 2010 Elsevier B.V. All rights reserved.
Sabil, K.M., Witkamp, G.-J., Peters, C.J.
Measurement and modeling of bubble and dew points of the carbon dioxide + tetrahydrofuran + water system
(2010) Journal of Chemical and Engineering Data, 55 (2), pp. 813-818.
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ABSTRACT: The bubble-and dew-point behavior of the carbon dioxide (1) + tetrahydrofuran (2) + water (3) system has been studied. Pressure-temperature isopleths were measured for the ternary system at x1) 0.01,0.02,0.03,0.04,0.09, and 0.27 at a constant mole fraction of tetrahydrofuran, x2) 0.05. The bubble-and dewpoint lines for the ternary systems were also measured at x2) 0.01,0.03,0.05, and 0.07 for fixed composition of carbon dioxide (x1) at 0.04 mol fraction and at x2) 0.01,0.03,0.05,0.06, and 0.09 for a fixed composition of carbon dioxide (x1) at 0.09, respectively. The pressure and temperature range from (1 to 6) MPa and (280 to 300) K, respectively. The experimental results for the ternary system have been modeled using the predictive Peng-Robinson-Stryjek-Vera (PRSV) equation of state with the Huron-Vidal-Orbey-Sandler (HVOS) mixing rule and the universal quasi-chemical activity coefficient (UNIQUAC) GEmodel. Excellent agreements have been found between the experimental and the predicted values of the bubble and dew points of the ternary system throughout the composition range studied. © 2010 American Chemical Society.
Sabil, K.M., Román, V.R., Witkamp, G.-J., Peters, C.J.
Experimental observations on the competing effect of tetrahydrofuran and an electrolyte and the strength of hydrate inhibition among metal halides in mixed CO2 hydrate equilibria
(2010) Journal of Chemical Thermodynamics, 42 (3), pp. 400-408.
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ABSTRACT: In the present work, experimental data on the equilibrium conditions of mixed CO2 and THF hydrates in aqueous electrolyte solutions are reported. Seven different electrolytes (metal halides) were used in this work namely sodium chloride (NaCl), calcium chloride (CaCl2), magnesium chloride (MgCl2), potassium bromide (KBr), sodium fluoride (NaF), potassium chloride (KCl), and sodium bromide (NaBr). All equilibrium data were measured by using Cailletet apparatus. Throughout this work, the overall concentration of CO2 and THF were kept constant at (0.04 and 0.05) mol fraction, respectively, while the concentration of electrolytes were varied. The experimental temperature ranged from (275 to 305) K and pressure up 7.10 MPa had been applied. From the experimental results, it is concluded that THF, which is soluble in water is able to suppress the salt inhibiting effect in the range studied. In all quaternary systems studied, a four-phase hydrate equilibrium line was observed where hydrate (H), liquid water (LW), liquid organic (LV), and vapour (V) exist simultaneously at specific pressure and temperature. The formation of this four-phase equilibrium line is mainly due to a liquid-liquid phase split of (water + THF) mixture when pressurized with CO2 and the split is enhanced by the salting-out effect of the electrolytes in the quaternary system. The strength of hydrate inhibition effect among the electrolytes was compared. The results shows the hydrate inhibiting effect of the metal halides is increasing in the order NaF < KBr < NaCl < NaBr < CaCl2 < MgCl2. Among the cations studied, the strength of hydrate inhibition increases in the following order: K+ < Na+ < Ca2+ < Mg2+. Meanwhile, the strength of hydrate inhibition among the halogen anion studied decreases in the following order: Br- > Cl- > F-. Based on the results, it is suggested that the probability of formation and the strength of ionic-hydrogen bond between an ion and water molecule and the effects of this bond on the ambient water network are the major factors that contribute to hydrate inhibition by electrolytes. © 2009.
Perrotin-Brunel, H., Perez, P.C., van Roosmalen, M.J.E., van Spronsen, J., Witkamp, G.-J., Peters, C.J.
Solubility of Δ9-tetrahydrocannabinol in supercritical carbon dioxide: Experiments and modeling
(2010) Journal of Supercritical Fluids, 52 (1), pp. 6-10.
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ABSTRACT: The solubility of Δ9-tetrahydrocannabinol (Δ9-THC) in supercritical carbon dioxide has been determined at 315, 327, 334 and 345 K and in the pressure range from 13.2 to 25.1 MPa using an analytical method with a quasi-flow apparatus. Prior to performing these measurements, the method was validated by measuring anthracene solubilities and comparing these with literature values. The molar solubility for Δ9-THC ranged from 0.20 to 2.95 × 10-4. The data were correlated using the Peng-Robinson equation of state in combination with quadratic mixing rules. Deviations between calculated results and the experimental data ranged from 4.1 to 13.3% absolute average relative deviation (AARD). © 2009 Elsevier B.V. All rights reserved.
Pronk, P., Infante Ferreira, C.A., Witkamp, G.J.
Mitigation of ice crystallization fouling in stationary and circulating liquid-solid fluidized bed heat exchangers
(2010) International Journal of Heat and Mass Transfer, 53 (1-3), pp. 403-411.
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ABSTRACT: Liquid-solid fluidized bed heat exchangers are attractive ice crystallizers since they are able to mitigate ice crystallization fouling and exhibit high heat transfer coefficients. Experiments show that the fouling removal ability of stationary fluidized beds increases with decreasing bed voidage (95-80%) and increasing particle size (2-4 mm). The removal of ice crystallization fouling appears to be more effective in circulating fluidized beds, especially at high circulation rates. Fouling removal is realized by both particle-wall collisions and pressure fronts induced by particle-particle collisions. A comparison between ice crystallization experiments and impact characteristics shows that the removal rate is proportional to the impulse exerted on the wall. A model based on these phenomena is discussed and predicts the transition temperature difference for ice crystallization fouling in both stationary and circulating fluidized beds with an average absolute error of 9.2%. © 2009 Elsevier Ltd. All rights reserved.
Sabil, K.M., Witkamp, G.-J., Peters, C.J.
Phase equilibria in ternary (carbon dioxide + tetrahydrofuran + water) system in hydrate-forming region: Effects of carbon dioxide concentration and the occurrence of pseudo-retrograde hydrate phenomenon
(2010) Journal of Chemical Thermodynamics, 42 (1), pp. 8-16.
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ABSTRACT: In the present work, the three- and four-phase hydrate equilibria of (carbon dioxide (CO2) + tetrahydrofuran (THF) + water) system are measured by using Cailletet equipment in the temperature and pressure range of (272 to 292) K and (1.0 to 7.5) MPa, respectively, at different CO2 concentration. Throughout the study, the concentration of THF is kept constant at 5 mol% in the aqueous solution. In addition, the fluid phase transitions of LW-LV-V → LW-LV (bubble point) and LW-LV-V → LW-V (dew point) are determined when they are present in the ternary system. For comparison, the three-phase hydrate equilibria of binary (CO2 + H2O) are also measured. Experimental measurements show that the addition of THF as a hydrate promoter extends hydrate stability region by elevating the hydrate equilibrium temperature at a specified pressure. The three-phase equilibrium line H-LW-V is found to be independent of the overall concentration of CO2. Contradictory, at higher pressure, the phase equilibria of the systems are significantly influenced by the overall concentration of CO2 in the systems. A liquid-liquid phase split is observed at overall concentration of CO2 as low as 3 mol% at elevated pressure. The region is bounded by the bubble-points line (LW-LV-V → LW-LV), dew points line (LW-LV-V → LW + V) and the four-phase equilibrium line (H + LW + LV + V). At higher overall concentration of CO2 in the ternary system, experimental measurements show that pseudo-retrograde behaviour exists at pressure between (2.5 and 5) MPa at temperature of 290.8 K. © 2009.
Dawes, G.J.S., Fratila-Apachitei, L.E., Necula, B.S., Apachitei, I., Witkamp, G.J., Duszczyk, J.
Release of PLGA-encapsulated dexamethasone from microsphere loaded porous surfaces
(2010) Journal of Materials Science: Materials in Medicine, 21 (1), pp. 215-221.
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ABSTRACT: The aim of the present study was to investigate the morphology and function of a drug eluting metallic porous surface produced by the immobilization of poly lactide-co-glycolide microspheres bearing dexamethasone onto plasma electrolytically oxidized Ti-6Al-7Nb medical alloy. Spheres of 20 μm diameter were produced by an oil-in-water emulsion/solvent evaporation method and thermally immobilized onto titanium discs. The scanning electron microscopy investigations revealed that the size distribution and morphology of the attached spheres had not changed significantly. The drug release profiles following degradation in phosphate buffered saline for 1000 h showed that, upon immobilisation, the spheres maintained a sustained release, with a triphasic profile similar to the non-attached system. The only significant change was an increased release rate during the first 100 h. This difference was attributed to the effect of thermal attachment of the spheres to the surface.
Waly, T., Munoz, R., Kennedy, M.D., Witkamp, G.J., Amy, G., Schippers, J.C.
Effect of particles on the induction time of calcium carbonate in synthetic SWRO concentrate
(2010) Desalination and Water Treatment, 18 (1-3), pp. 103-111.
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ABSTRACT: Particles, which are naturally present in seawater, have been reported to affect the formation of CaCO3 crystals. In this study the effect of foreign particles on induction time was explored. Induction time was monitored using a highly sensitive pH meter mounted in an air-tight glass reactor. Experimental work was performed with synthetic seawater prepared using ultra-pure water with a composition equivalent to 50% recovery SWRO concentrate (based on the composition of seawater from the Gulf of Oman). The prepared synthetic solutions were filtered through filters having different pore sizes namely 0.22 μm; 0. μm and 100kD (≈0.03 μm). In addition, glass beads of diameter 20-30 nm were added in volumes of (1; 0.5 and 0.1 ml) to synthetic seawater to yield an increase in glass/water contact area of 123%, 16% and 1% compared to the total reactor glass area in contact with the synthetic water. Different mixing speeds were applied namely 10; 50; 150 and 300 rpm to investigate the effect of mixing on experimental results. Results showed that filtering synthetic seawater and applying different mixing speeds had a negligible effect on the experimental induction time results. On the contrary, the addition of glass beads shortened the induction time substantially from 30% to 100% (immediate precipitation), depending on the amount of beads added. © 2010 Desalination Publications. All rights reserved.
Kühne, E., Witkamp, G.J., Peters, C.J.
Ionic liquids and carbon dioxide as combined solvents for reactions and separations: The miscibility switch
(2009) Current Trends of Supercritical Fluid Technology in Pharmaceutical, Nutraceutical and Food Processing Industries, pp. 61-70.
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ABSTRACT: Ionic liquids (ILs) and carbon dioxide (CO2) are emerging as candidates to replace volatile organic solvents in synthesis and extraction processes. ILs are a relatively new class of substances composed only of ions and liquid at temperatures below 100oC. As a major attractive characteristic, they have negligible vapor pressure - reducing solvent loss by evaporation and environmental pollution. When used simultaneously with carbon dioxide for reactions and extractions, the process will be based on non-toxic, non-flammable solvents and will be applicable for a wide variety of compounds. It has been recently shown that carbon dioxide can be used to split phases in homogenous one-phase systems with ILs. This miscibility switch allows reactions to be carried out in one phase, and by simply changing CO2 pressure, extractions can be carried out more efficiently under heterogeneous conditions. This chapter presents an overview on ionic liquids and carbon dioxide, together with an explanation on the phenomenon of miscibility switch. © 2010 Bentham Science Publishers Ltd. All rights reserved.
Tavares Cardoso, M.A., Marcotulio, G., Van Spronsen, J., Witkamp, G.-J., De Jong, W., Van Ruud Ommen, J.
Dissolution and fractionation of wood and straw using ionic liquids
(2009) Conference Proceedings - 2009 AIChE Annual Meeting, 09AIChE, 1 p.
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ABSTRACT: The decrease in the resources of fossil fuels together with the global warming alarms have led to an intensified search for alternative fuels to supply the modern society. Among them, the concept of biorefinery is becoming increasingly important since it presents the potential to be a real alternative for large scale production of fuels with a neutral carbon dioxide balance. In this biorefinery context, biomass resources such as wood and straw have not yet been properly valorised since these materials are mostly incinerated to produce heat. In addition, production of fuels from lignocellulosic biomass, especially wood, minimizes the competition with the food chain and presents higher yields when compared to first generation biofuels. The challenge now is to make this process attractive from an economical point-of-view. One of the major difficulties when dealing with these raw materials is related with the need of pre-treatments to dissociate the biomass structure. Lignocellulose consists mainly of cellulose (35 -50%), hemicellulose (20 -35%) and lignin (5-30%). These components are assembled in a complex three-dimensional structure remarkably resistant against chemicals and microbial attacks that makes them very difficult to hydrolyze, which is key for its future utilization. An effective dissociation of these components and their separation can lead to the production of several high value products prior to the production of fuels. This integrated approach increases the competitiveness of the biorefinery industry and can make it attractive even considering the actual oil prices (2009). As previously reported, ionic liquids offer a new and attractive route for the dissolution of lignocellulosic biomass. Besides the amount of biomass that can be dissolved in some ionic liquids (that can reach 8 % w/w), their complete recycling and significant environmental advantages make this class of compounds the best possible choice for a new pre-treatment to dissolve and fractionating the lignocellulosic biomass prior to biorefinery processing. In this work, the complete dissolution of both wood and wheat straw in ionic liquids was followed by the fractionation of the several components that constitute the biomass and the analysis of each fraction was performed to close the mass balance. Two different ionic liquids, 1-ethyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium chloride, and their mixtures were tested. The results were compared both in terms of yield and selectivity for the different constituents of both types of biomass. The obtained results show that this is a promising process for the pre-treatment of lignocellulosic biomass, regardless the type (wood or straw). Moreover, since the ionic liquids can be almost 100% recycled, this is a low cost, fast, simple and environmentally friendly pre-treatment that can increase significantly the competitiveness of modern biorefineries.
Kroon, M.C., Docherty, H., Cummings, P.T., Peters, C.J., Witkamp, G.-J., Mao, W.L.
Novel high capacity hydrogen storage materials based on tetrahydrogenmethane
(2009) Conference Proceedings - 2009 AIChE Annual Meeting, 09AIChE, 1 p.
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ABSTRACT: Hydrogen is considered to be a promising alternative to fossil fuels. Unfortunately, due to the difficulty in finding a practical storage medium, its use as a fuel, for instance for application in the automotive sector, is currently limited. In order to be considered practical, a hydrogen storage material should satisfy a number of requirements, including a high storage capacity (high hydrogen content by mass and volume), ambient storage temperature and pressure, a fast uptake of hydrogen, and reversible hydrogen release. So far, a material that meets these requirements is does not exist. In this work, we develop novel hydrogen storage materials that fulfills the above-mentioned requirements. The idea is to store hydrogen in the hydrogen-rich crystalline molecular compound tetrahydrogenmethane (CH4(H2)4), which contains as much as 33.4 wt% molecular hydrogen. Not much is known about how this material stores such a remarkable amount of molecular hydrogen: Even something as basic as its structure has not yet been identified. Motivated by this, we investigate the structure of tetrahydrogenmethane, as well as the interaction of hydrogen with this material, using a combined experimental - molecular simulation approach. We also identify promoters that may be added to this material to decrease the necessary storage pressure. Results will be presented at the conference.
Nugteren, H.W., Butselaar-Orthlieb, V.C.L., Izquierdo, M., Witkamp, G.-J., Kreutzer, M.T.
High strength geopolymers from fractionated and pulverized fly ash
(2009) 3rd World of Coal Ash, WOCA Conference - Proceedings, .
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ABSTRACT: Coal combustion residues are ideal precursors for the production of geopolymer cements. Activated in alkaline solutions, fly ash provides the necessary Si and Al for the polymer chains that form the matrix of the hardened product. Potassium silicate and blast furnace slag are added to enhance the strength developed. Compressive strength values of over 100 MPa are obtained in these matrices, much higher than observed with normal Ordinary Portland Cement binders. Besides the chemistry, also the physical characteristics of the fly ash are of importance for the development of high strength. The fine particle size and the high sphericity of the particles, both favor good and dense packing of the material into the matrix. In order to further benefit from the physical characteristics of fly ash, size fractions were separated and geopolymers produced from them. However, the relation between size and strength was not clear, mainly due to the fact that, when separating, the chemistry of the different fractions turned out to be different as well. This was clearly reflected by the difference in pH for the fractions (varying from 10.2 to 12.5). When size fractions were obtained by grinding, the chemistry was much less affected as shown by a much smaller pH variation of the ground fractions (11.1 to 11.6). Furthermore, a relation between geopolymer compressive strength and fly ash particle size becomes apparent. Workability seems to be influenced by free lime content of the ash. The addition of K2HPO4 helps to extend the working time for the paste.
Sabil, K.M., Witkamp, G.-J., Peters, C.J.
Phase equilibria of mixed carbon dioxide and tetrahydrofuran hydrates in sodium chloride aqueous solutions
(2009) Fluid Phase Equilibria, 284 (1), pp. 38-43.
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ABSTRACT: In this work, the competing effects of sodium chloride (NaCl) and tetrahydrofuran (THF) on carbon dioxide hydrate formation are investigated through phase equilibrium measurements. The phase behaviour in the hydrate forming region for the binary system carbon dioxide-water, the ternary systems carbon dioxide-tetrahydrofuran-water and ternary carbon dioxide-sodium chloride-water and, in addition, the quaternary system carbon dioxide-tetrahydrofuran-water-sodium chloride are determined experimentally, using a Cailletet apparatus. All measurements are made in a temperature and pressure region of 275-290 K and 0.5-7.0 MPa, respectively. In these ranges, three different hydrate equilibrium curves are measured namely: H-LW-V, H-LW-LV-V and H-LW-LV. The formation of an organic-rich liquid phase in the systems due to a liquid-liquid two-phase split between water and tetrahydrofuran when pressurized with carbon dioxide causes the occurrence of an upper quadruple point (Q2) to evolve into a four-phase H-LW-LV-V equilibrium line. The presence of sodium chloride in the quaternary system enhances the split between the two liquids due to the salting-out effect. It was found that the hydrate promoting effect of tetrahydrofuran is able to suppress the inhibiting effect of sodium chloride especially at lower concentration of sodium chloride. © 2009.
Pascual, M.R., Derksen, J.J., Van Rosmalen, G.M., Witkamp, G.J.
Flow and particle motion in scraped heat exchanger crystallizers
(2009) Chemical Engineering Science, 64 (24), pp. 5153-5161.
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ABSTRACT: Turbulent fluid flow and related solid particle behaviour in the direct vicinity of the heat exchanging (HE) surface of a scraped heat exchanger crystallizer was studied. The liquid flow is visualized by dye injection and the particles are monitored directly for two types of commonly used scraper geometries. In conjunction with this experimental work, we performed direct numerical simulations of the two-phase (solid-liquid) flow system. Our main goal is the design of scraper geometries that enhance heat transfer by perturbing the thermal boundary layer, and effectively scrape off particles that nucleate, grow and adhere onto the HE surface. Also the turbulent flow generated by the moving scrapers should direct the particles into the bulk of the tank. The experiments and simulations show good qualitative resemblance which enables the design of scrapers based primarily on numerical predictions. © 2009 Elsevier Ltd. All rights reserved.
Elif Genceli, F., Horikawa, S., Iizuka, Y., Sakurai, T., Hondoh, T., Kawamura, T., Witkamp, G.-J.
Meridianiite detected in ice
(2009) Journal of Glaciology, 55 (189), pp. 117-122.
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ABSTRACT: Inclusions affect the behavior of ice, and their characteristics help us understand the formation history of the ice. Recently, a low-temperature magnesium sulfate salt was discovered. This paper describes this naturally occurring MgSO4· 11H2O mineral, meridianiite, derived from salt inclusions in sea ice of Lake Saroma, Japan and in Antarctic continental core ice. Its occurrence is confirmed by using micro-Raman spectroscopy to compare Raman spectra of synthetic MgSO 4 ·-11H2O with those of the inclusions.
Pronk, P., Infante Ferreira, C.A., Witkamp, G.J.
Prevention of fouling and scaling in stationary and circulating liquid-solid fluidized bed heat exchangers: Particle impact measurements and analysis
(2009) International Journal of Heat and Mass Transfer, 52 (15-16), pp. 3857-3868.
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ABSTRACT: Fluidized particles in liquid-solid fluidized bed heat exchangers are able to remove deposits from the walls and thus to prevent fouling or scaling. This fouling prevention ability is believed to depend strongly on the frequency and force of particle-wall collisions. This paper presents piezoelectric measurements of impacts on the wall in both stationary and circulating fluidized beds of various particle sizes and bed voidages. Two types of impacts were measured, namely by collisions of particles on the sensor and by liquid pressure fronts induced by particle-particle collisions close to the sensor. The characteristics of both impact types are used to analyze the total impulse and energy exerted by impacts on the wall for various fluidized beds. © 2009.
Kühne, E., Alfonsín, L.R., Martinez, M.T.M., Witkamp, G.-J., Peters, C.J.
Comment on "characterization of the ability of CO2 to act as an antisolvent for ionic liquid/ organic mixtures"
(2009) Journal of Physical Chemistry B, 113 (18), pp. 6579-6580.
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Kühne, E., Martin, A., Witkamp, G.-J., Peters, C.J.
Modeling the phase behavior of ternary systems ionic liquid + organic + c02 with a group contribution equation of state
(2009) AIChE Journal, 55 (5), pp. 1265-1273.
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ABSTRACT: This work presents the results of the use of a Group Contribution Equation of State (GC-EOS) to model experimental data obtained for ternary systems of the type bmim[BF4] + organic solute + CO2 with four different organic compounds, namely acetophenone, 1-phe-nylethanol, 4- isobutylacetophenone, and 1-(4-isobutylphenyl)-ethanol. Our results show that the GC-EOS is able to qualitatively predict not only L+V→L but also L 1+L2→L phase transitions. As the two two-phase boundaries L+V and L1+L2 of the experimentally found three-phase region L1+L2+V almost coincide with the saturated vapor pressure curve of pure CO2, the phase transitions L+V→L1+L2+V and L1+L2+V→ L1+L2 have been represented as this vapor-pressure curve by the model. The average absolute deviations between experimental and predicted values for all phase transitions have been found to be very satisfactory. © 2009 American Institute of Chemical Engineers AIChE J, 55: 1265-1273, 2009.
Rodriguez Pascual, M., Ravelet, F., Delfos, R., Derksen, J.J., Witkamp, G.J.
Large eddy simulations and stereoscopic particle image velocimetry measurements in a scraped heat exchanger crystallizer geometry
(2009) Chemical Engineering Science, 64 (9), pp. 2127-2135.
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ABSTRACT: The transport phenomena in scraped heat exchanger (HE) crystallizers are critical for the process performance. Fluid flow and turbulence close to the HE surface as generated by stirring elements and scraper blades are crucial in this respect as they aim at avoiding an insulating scale layer on the HE surface. For this reason we performed large-eddy simulations of the turbulent flow (at a Reynolds number of 5×104) in a typical cooling crystallizer geometry with a focus on the bottom region where the heat exchanging surface was located. The flow simulations were validated with stereoscopic PIV experiments performed higher up in the crystallizer. Water at a constant temperature was the working fluid in the experiments as well as in the simulations. For reasons of optical accessibility being hindered by the scrapers, the experiments could not be done near the heat exchanging surface. The flow structures as revealed by the large-eddy simulations could explain the local occurrence of scaling on an evenly cooled HE surface, and its irreproducibility caused by instantaneous cold spots. © 2009 Elsevier Ltd. All rights reserved.
Dawes, G.J.S., Fratila-Apachitei, L.E., Mulia, K., Apachitei, I., Witkamp, G.-J., Duszczyk, J.
Size effect of PLGA spheres on drug loading efficiency and release profiles
(2009) Journal of Materials Science: Materials in Medicine, 20 (5), pp. 1089-1094.
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ABSTRACT: Drug delivery systems (DDS) based on poly (lactide-co-glycolide) (PLGA) microspheres and nanospheres have been separately studied in previous works as a means of delivering bioactive compounds over an extended period of time. In the present study, two DDS having different sizes of the PLGA spheres were compared in morphology, drug (dexamethasone) loading efficiency and drug release kinetics in order to investigate their feasibility with regard to production of medical combination devices for orthopedic applications. The loaded PLGA spheres have been produced by the oil-in-water emulsion/solvent evaporation method following two different schemes. Their morphology was assessed by scanning electron microscopy and the drug release was monitored in phosphate buffer saline solution at 37°C for 550 h using high performance liquid chromatography. The synthesis schemes used produced spheres with two different and reproducible size ranges (20 ± 10 and 1.0 ± 0.4 μm) having a smooth outer surface and regular shape. The drug loading efficiency of the 1.0 μm spheres was found to be 11% as compared to just 1% for the 20 μm spheres. Over the 550 h release period, the larger spheres (diameter 20 ± 10 μm) released 90% of the encapsulated dexamethasone in an approximately linear fashion whilst the relatively small spheres (diameter 1.0 ± 0.4 μm) released only 30% of the initially loaded dexamethasone, from which 20% within the first 25 h. The changes observed were mainly attributed to the difference in surface area between the two types of spheres as the surface texture of both systems was visibly similar. As the surface area per unit volume increases in the synthesis mixture, as is the case for the 1.0 μm spheres formulation, the amount of polymer-water interfaces increases allowing more dexamethasone to be encapsulated by the emerging polymer spheres. Similarly, during the release phase, as the surface area per unit volume increases, the rate of inclusion of water into the polymer increases, permitting faster diffusion of dexamethasone.
Genceli, F.E., Pascual, M.R., Kjelstrup, S., Witkamp, G.-J.
Coupled heat and mass transfer during crystallization of MgS04 7H2O on a cooled surface
(2009) Crystal Growth and Design, 9 (3), pp. 1318-1326.
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ABSTRACT: Crystal growth of MgS04 aqueous solution on a cooled surface has been studied theoretically and experimentally. The excess entropy production rate for heat and mass transport into, out of, and across the interface was used to define the fluxes and forces of the system. The method describes the interface as a separate (two-dimensional) phase in local equilibrium. Coupled heat and mass flux equations from non-equilibrium thermodynamics were defined for crystal growth and the temperature jump at the interface of the growing crystal. All interface transfer resistivities were determined using MgS0 4.7H2O crystallization on a cooled surface as an example case. The coupling coefficient showed that between 20 and 30% of the enthalpy of crystallization is returned to the liquid side during crystal growth. The coupling of heat and mass transport equations at the liquid-solid interface has not been described before. © 2009 American Chemical Society.
Waly, T., Saleh, S., Kennedy, M.D., Witkamp, G.J., Amy, G., Schippers, J.C.
Will calcium carbonate really scale in seawater reverse osmosis?
(2009) Desalination and Water Treatment, 5 (1-3), pp. 146-152.
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ABSTRACT: The elimination of antiscalant chemicals in SWRO plants will result in a more environmentally friendly, sustainable and cheaper process. Practically, this can be achieved by determining the real scaling limits of calcium carbonate in SWRO. In supersaturated solutions the period of metastability before the start of crystal growth is commonly indicated as induction time (tind). Induction time longer than the average retention time of concentrate in a single-stage SWRO suggests that scaling will probably not occur. This research project aims to determine the induction times as a function of the saturation index and ionic strength for synthetic seawater. The experimental procedure utilized in this research is a sensitive and stable pH meter with accuracy of 0.01 pH units. The pH meter used was able to detect precipitation as low as 0.3 mg/l of CaCO3. Induction time experiments were performed with synthetic concentrates with low and high ionic strength. The synthetic high ionic strength solution had the same ionic strength, Ca2+ and HCO3 - concentrations as the SWRO concentrate at a recovery of 30% and utilizing water from the Gulf of Oman. The lower ionic strength solution comprise the same Ca2+ and HCO3 - concentrations as of the high ionic solution but with lower NaCl content. Results showed a good correlation between the logarithm of the induction time and saturation index. The pH of SWRO concentrate with (30% recovery) is expected to be in the range of 8.25-8.3. Experimental results showed an induction time of almost 30 min using synthetic concentrate which is ca. 10-15 times longer than the average retention time of concentrate in a singlestage SWRO (2-3 min). These results need to be verified with real SWRO concentrate. © 2009 Desalination Publications.
Dawes, G., Fratila-Apachitei, L.E., Apachitei, I., Witkamp, G.J., Duszczyk, J.
Particulate drug delivery systems for P/M medical combination devices
(2009) Proceedings of the Euro International Powder Metallurgy Congress and Exhibition, Euro PM 2009, 2, .
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ABSTRACT: P/M technology is used in orthopedic implants to create porous surfaces for bone ingrowth. However, these porous surfaces can be exploited for the storage of biofunctional particles in order to generate multifunctional surfaces needed to fight against peri-implant infection or enhance osseointegration. The morphology and release kinetics of several drug delivery systems combining poly(lactide-co-glycolide) particles with porous metallic surfaces were compared to investigate their use for P/M medical combination devices. The drug loaded poly(lactide-co-glycolide) microparticles were produced by an oil-in-water emulsion/solvent evaporation method. The larger particles (26±10 μm) showed a triphasic drug release profile regardless of the type of surface they were attached to, and a sustained release could be achieved for at least 650 hours. The smaller particles (0.6±0.3 μm) attached to a surface having a pore size of 1.1±0.3 μm showed only burst release kinetics of the encapsulated drug. The applications of such systems for porous surfaces obtained by P/M technology are discussed.
Damen, M.R., Brand, R.W., Bloem, S.C., Pingen, E., Steur, K., Peters, C.J., Witkamp, G.-J., Kroon, M.C.
Process intensification by combining ionic liquids and supercritical carbon dioxide applied to the design of Levodopa production
(2009) Chemical Engineering and Processing: Process Intensification, 48 (1), pp. 549-553.
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ABSTRACT: By combining ionic liquids and supercritical carbon dioxide a new class of intensified processes comes into perspective. This is illustrated here in a novel conceptual design for Levodopa production based on a recently granted patent [M.C. Kroon, A. Shariati, L.J. Florusse, C.J. Peters, J. van Spronsen, G.J. Witkamp, R.A. Sheldon, K.E. Gutkowski, Process for carrying out a chemical reaction, International Patent WO 2006/088348 A1 (2006)], which uses an ionic liquid and supercritical carbon dioxide as solvents in the slowest processing step. Compared to the conventional Levodopa production, the energy consumption in this processing step is reduced from 22.9 MJ/kg product to 17.4 MJ/kg product, the replacement of deactivated catalyst is reduced from 276 mg/kg product to 2.3 mg/kg product, solvent replacement is reduced from 2.68 kg/kg product to 0.03 kg/kg product and the variable costs, excluding raw materials, are reduced from 6.49 €/kg product to 0.68 €/kg product using this novel concept. However, the estimated investment costs of the novel process concept are expected to be higher (in the order of 14 M€). Yet, the payback time is only 1.6 years. © 2008.
Pronk, P., Infante Ferreira, C.A., Witkamp, G.J.
Prevention of crystallization fouling during eutectic freeze crystallization in fluidized bed heat exchangers
(2008) Chemical Engineering and Processing: Process Intensification, 47 (12), pp. 2140-2149.
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ABSTRACT: Eutectic freeze crystallization is a promising separation technique to produce salt and ice crystals with very high purities and requires less energy than competitive evaporative crystallization techniques. A drawback of this technique is crystallization fouling, which seriously reduces heat transfer rates. Solid-liquid fluidized bed heat exchangers may be attractive crystallizers for this purpose, since they have demonstrated to prevent severe crystallization fouling, for example of ice crystals. This paper presents crystallization experiments with a single-tube fluidized bed heat exchanger. A first experimental series showed that fluidized beds are also able to prevent salt fouling during cooling crystallization from KNO3 or MgSO4 solutions. A second series revealed that fouling during eutectic freeze crystallization is more severe than during separate salt or ice crystallization and is therefore difficult to prevent by the fluidized bed. The explanation for this phenomenon is that the salt crystallization process strongly reduces the solute mass transfer limitation for ice crystals growing on the wall resulting in an increased growth rate and more severe crystallization fouling. The addition of a non-crystallizing component strongly reduces fouling and enables to perform eutectic freeze crystallization in fluidized bed heat exchangers for industrial applications. © 2007 Elsevier B.V. All rights reserved.
Karakatsani, E.K., Economou, I.G., Kroon, M.C., Bermejo, M.D., Peters, C.J., Witkamp, G.-J.
Equation of state modeling of the phase equilibria of ionic liquid mixtures at low and high pressure
(2008) Physical Chemistry Chemical Physics, 10 (40), pp. 6160-6168.
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ABSTRACT: Accurate design of processes based on ionic liquids (ILs) requires knowledge of the phase behavior of the systems involved. In this work, the truncated perturbed chain polar statistical associating fluid theory (tPC-PSAFT) is used to correlate the phase behavior of binary and ternary IL mixtures. Both non-polar and polar solvents are examined, while methyl imidazolium ILs are used in all cases. tPC-PSAFT accounts explicitly for weak dispersion interactions, highly directive polar interactions between permanent dipolar and quadrupolar molecules and association between hydrogen bonding molecules. For mixtures of non-polar solvents, tPC-PSAFT predicts accurately the binary mixture data. For the case of polar solvents, a binary interaction parameter is fitted to the experimental data and the agreement between experiment and correlation is very good in all cases. © the Owner Societies.
Bouchard, A., Jovanović, N., de Boer, A.H., Martín, A., Jiskoot, W., Crommelin, D.J.A., Hofland, G.W., Witkamp, G.-J.
Effect of the spraying conditions and nozzle design on the shape and size distribution of particles obtained with supercritical fluid drying
(2008) European Journal of Pharmaceutics and Biopharmaceutics, 70 (1), pp. 389-401.
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ABSTRACT: In the perspective of production of dry therapeutic protein formulations, spray drying of lysozyme (as a model protein) into supercritical carbon dioxide was studied. The effects of the nozzle (i.e., co-current coaxial converging and converging-diverging, and T-mixer impinging) and process conditions (i.e., flow rates, pressure) on the drying of the lysozyme prepared in aqueous solution dried with supercritical carbon dioxide enriched with ethanol were investigated. The particle size distribution, width of particle size distribution and morphology were used to determine the effect of the various parameters assessed. Particles with a median size of ∼1.5, ∼5 or ∼25 μm were produced depending of the nozzle selected. A basic comparative study of the nozzle was done by computational fluid dynamics, but the differences in particle size could not be depicted by these computations. The proportional increase of the flow rates (up to fivefold) caused a decrease in particle size (7- to 12-fold), and doubling the pressure caused a moderate decrease of the size (5-20%). The individual effect of the supercritical carbon dioxide, ethanol and solution streams was explained with a mass transfer model. Changing the ratio between flow rates slightly affected the particle size in various ways because of the swelling and shrinking stages of the drying droplet in supercritical carbon dioxide enriched with ethanol. © 2008 Elsevier B.V. All rights reserved.
Kühne, E., Witkamp, G.-J., Peters, C.J.
High-pressure phase behavior of ternary mixtures with ionic liquids, part I: The system bmim[BF4]+4-isobutylacetophenone + CO2
(2008) Green Chemistry, 10 (9), pp. 929-933.
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ABSTRACT: Performing reactions in a homogeneous system is extremely important for the achievement of high reaction rates and yield. Since carbon dioxide can tune the miscibility of ionic liquid/organic mixtures, measurements on the phase behavior of these systems provide useful information for the selection of operational conditions for reactions and extractions. We investigated the phase behavior of ternary mixtures of the type bmim[BF4] + solute + CO 2, in which the solute is an intermediary in the synthesis of ibuprofen. In this contribution, the influence of carbon dioxide pressure on the location of the homogeneous liquid phase region in the phase diagram of the ternary system bmim[BF4] + 4-isobutylacetophenone + CO2 is presented. We show that for CO2 concentrations above 60 mol%, a narrow three-phase region can be found in the pressure versus temperature diagram, and that a further increase in CO2 composition gradually reduces the extension and influences the location of the one-phase liquid region, finally resulting in its complete disappearance. © The Royal Society of Chemistry.
Kühne, E., Santarossa, S., Perez, E., Witkamp, G.J., Peters, C.J.
New approach in the design of reactions and separations using an ionic liquid and carbon dioxide as solvents: Phase equilibria in two selected ternary systems
(2008) Journal of Supercritical Fluids, 46 (2), pp. 93-98.
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ABSTRACT: Due to mainly environmental and safety reasons, green chemistry is receiving a great deal of attention in the last couple of years. The development of more benign, environmentally friendly processes with less hazardous solvents is currently the major focus of a wide variety of research activities. However, the development of efficient processes requires knowledge on the phase equilibria of the system, which are unfortunately poorly studied. Therefore, in this study we present the phase equilibria for ternary mixtures of an ionic liquid, carbon dioxide (CO2) and two organic solutes, namely 1-phenylethanol and acetophenone, at CO2 concentrations varying from 10 up to 50 mol%. The two organic solutes studied are the reactant and product of the hydrogenation of acetophenone into 1-phenylethanol. Data were measured for pressures up to 14 MPa and over a temperature range from 278 to 370 K. © 2008 Elsevier B.V. All rights reserved.
Pronk, P., Infante Ferreira, C.A., Witkamp, G.J.
Superheating of ice slurry in melting heat exchangers
(2008) International Journal of Refrigeration, 31 (5), pp. 911-920.
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ABSTRACT: One of the main components of an ice slurry system is the melting heat exchanger, in which ice slurry absorbs heat resulting in the melting of ice crystals. Design calculations of melting heat exchangers are mainly based on heat transfer and pressure drop data, but recent experimental studies have shown that superheating of ice slurry should also be considered. This paper presents ice slurry melting experiments with a tube-in-tube heat transfer coil. The experimental results indicate that operating conditions such as ice slurry velocity, heat flux, solute concentration, ice fraction, and ice crystal size determine the degree of superheating. The various influences are explained by considering the melting process as a two-stage process consisting of the heat transfer between wall and liquid and the combined heat and mass transfer between liquid and crystals. Bigger ice crystals and higher solute concentrations decrease the rate of the second stage and therefore increase the degree of superheating. © 2007 Elsevier Ltd and IIR.
Kühne, E., Santarossa, S., Witkamp, G.-J., Peters, C.J.
Phase equilibria in ternary mixtures of the ionic liquid bmim[BF 4], (S)-naproxen and CO2 to determine optimum regions for green processing
(2008) Green Chemistry, 10 (7), pp. 762-766.
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ABSTRACT: In order to optimize reaction and separation processes, knowledge of the phase behaviour of the system is of fundamental importance. In this contribution we present the solid-liquid and liquid-vapour equilibria of the ternary system 1-butyl-3-methylimidazolium tetrafluoroborate + (S)-naproxen + carbon dioxide. Five different samples were studied, with CO2 concentrations ranging from 10 to 50 mol%, and pressure and temperature conditions of 1 to 14 MPa, and 310 to 370 K, respectively. It is shown that the amount of CO2 influences not only the location of the homogeneous liquid phase region, but also the extension of the region in which it occurs. Based on the collected experimental data, optimum pressure and temperature conditions can be selected for the precipitation of (S)-naproxen from the ionic liquid in order to improve the efficiency of the separation. © The Royal Society of Chemistry.
Kühne, E., Calvo, E.S., Witkamp, G.J., Peters, C.J.
Fluid phase behaviour of the ternary system bmim[BF4] + 1-(4-isobutylphenyl)-ethanol + carbon dioxide
(2008) Journal of Supercritical Fluids, 45 (3), pp. 293-297.
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ABSTRACT: To investigate the possibility of carrying out a reaction in the medium ionic liquid/supercritical CO2 as mixed solvents, the solubility of carbon dioxide in the mixture 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF4]) + 1-(4-isobutylphenyl)-ethanol has been investigated. Measurements were carried out in a Cailletet apparatus at pressures up to 14 MPa. In the temperature range from 278 K to 368 K, the solubility of CO2 in the mixture was found to slightly decrease in comparison with the solubility in pure bmim[BF4]. The effect of the solute nature has been investigated by comparing the results with two other ternary systems previously investigated, with 4-isobutylacetophenone and 1-phenylethanol as organic solutes. The results have shown that even similar molecules can affect the solubility of CO2 in the bmim[BF4] + organic mixture in different ways, with higher solubility of carbon dioxide for ketones as solute rather than an alcohol and that the addition of an alkyl group to solute molecules with the same functional group will most likely facilitate carbon dioxide solubility. © 2008 Elsevier B.V. All rights reserved.
Kühne, E., Perez, E., Witkamp, G.J., Peters, C.J.
Solute influence on the high-pressure phase equilibrium of ternary systems with carbon dioxide and an ionic liquid
(2008) Journal of Supercritical Fluids, 45 (1), pp. 27-31.
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ABSTRACT: To study the potential of performing hydrogenation reactions in ionic liquid-CO2 media, the high-pressure phase equilibrium of the ternary system 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF4]) + 4-isobutylacetophenone + carbon dioxide (CO2) has been investigated. Experiments were performed in the Cailletet apparatus in a temperature range from 278.15 up to 368.15 K while pressures up to 14 MPa were applied. In this system, not only liquid-vapor boundaries were found, but also at high CO2 concentrations liquid-liquid biphasic equilibrium occurred.11Additional experiments are in progress. These results will be presented in a subsequent contribution. A comparison between the experimental results of this work, the data collected for the binary system bmim[BF4] + CO2 and a ternary system with acetophenone as the solute shows that the type of solute added can dramatically change the phase behavior of the system. © 2007 Elsevier B.V. All rights reserved.
Bouchard, A., Jovanović, N., Hofland, G.W., Crommelin, D.J.A., Jiskoot, W., Witkamp, G.-J.
Ways of manipulating the polymorphism of glycine during supercritical fluid crystallisation
(2008) Journal of Supercritical Fluids, 44 (3), pp. 422-432.
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ABSTRACT: The precipitation of glycine from aqueous solution was studied using a mixture of supercritical carbon dioxide and ethanol as drying medium and as anti-solvent. Glycine, which has three polymorphs, was precipitated by a direct spraying process using a coaxial nozzle under high pressure. By simple manipulation of the solute concentration, the process could be tuned to selectively precipitate either pure α or β-glycine, as determined by X-ray powder diffraction. When decreasing the solute concentration or increasing the ethanol fraction in the system, the precipitation of the metastable β-glycine was preferred over the precipitation of α-glycine. Modelling of the mass transfer around a drop showed that the ethanol fraction inside the drop can reach significant values, and that the evaporation occurs in less than a second, leaving little space for recrystallisation. Even though the crystal growth rate was extreme (up to 800 μm/s), the product was crystalline. © 2007.
Bouchard, A., Jovanović, N., Martín, A., Hofland, G.W., Crommelin, D.J.A., Jiskoot, W., Witkamp, G.-J.
Effect of the modifier on the particle formation and crystallisation behaviour during precipitation from aqueous solutions
(2008) Journal of Supercritical Fluids, 44 (3), pp. 409-421.
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ABSTRACT: Ethanol is a commonly added modifier to supercritical CO2 for particle formation from aqueous solutions. Four modifiers - methanol, ethanol, 2-propanol and acetone - were studied to determine the extent of the effect of the modifier selection on the particles produced and to determine more precisely the precipitation mechanisms. The strong anti-solvent effect of methanol on the solute was shown by the production of metastable β-glycine, phenylalanine anhydrate and lysozyme agglomerated nanoparticles. Ethanol showed such an anti-solvent effect only when use at higher fraction in the supercritical phase, followed by 2-propanol and acetone. 2-Propanol and acetone mainly contributed to the precipitation of the solute by increasing the solubility of the water in the supercritical phase. In such precipitation conditions the more stable α-glycine, phenylalanine monohydrate and lysozyme microspheres were produced by the evaporation of the solution into the CO2 phase. The putative anti-solvent effect of CO2 in the systems studied was not clearly observed, but it remains that CO2 is essential to the SCF-drying process. © 2007.
Nieborg, V.H.J., Markesteijn, A.P., Lindken, R.H., Witkamp, G.J., Kramer, H.J.M., Westerweel, J.
Mixing with EOF for a precipitation reaction
(2008) Journal of Dispersion Science and Technology, 29 (4), pp. 587-592.
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ABSTRACT: Microfluidics is becoming increasingly more interesting for chemical engineering applications. This article takes a closer look at the possibilities of performing a precipitation reaction in a microfluidic device. This specific type of reaction demands for instance fast mixing. We take sodium chloride precipitation as a model anti-solvent precipitation reaction. Effective mixing is achieved by applying an electric field over the fluid. The dispersion of a plug is measured when it is transported by pressure driven flow or electroosmotic flow. These two different types of transportation are investigated.
Shariati, A., Sheldon, R.A., Witkamp, G.-J., Peters, C.J.
Enantioselective catalytic hydrogenation of methyl α-acetamido cinnamate in [bmim][BF4]/CO2 media
(2008) Green Chemistry, 10 (3), pp. 350-354.
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ABSTRACT: The homogeneously-catalyzed hydrogenation reaction of methyl α-acetamido cinnamate (MAC) was chosen to evaluate the feasibility of combining the advantages of ionic liquids (ILs) as solvents for reactions and the chiral complexes as catalysts for enantioselective reactions. 1-Butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and (-)-1,2-bis((2R,5R)-2,5-dimethylphospholano)benzene (cyclooctadiene)rhodium(i) tetrafluoroborate (Rh-MeDuPHOS) were selected as the solvent and the catalyst, respectively. All experiments were carried out in an autoclave. The Rh-MeDuPHOS catalyst dissolved in [bmim][BF4] was able to hydrogenate MAC with high conversions and enantioselectivities. The effects of hydrogen (H 2) pressure on the conversion and enantioselectivity of MAC hydrogenation were studied. It was shown that with increasing H2 pressure, the conversion increases while the selectivity decreases. Adding carbon dioxide (CO2) as a potential enhancer of this reaction was also studied. It was shown that by increasing the partial pressure of CO 2, the conversion decreases, while the selectivity increases. Catalyst recycling by extraction of the product with methyl tert-butyl ether (MTBE) was also possible. This journal is © The Royal Society of Chemistry.
Kroon, M.C., Toussaint, V.A., Shariati, A., Florusse, L.J., Van Spronsen, J., Witkamp, G.-J., Peters, C.J.
Crystallization of an organic compound from an ionic liquid using carbon dioxide as anti-solvent
(2008) Green Chemistry, 10 (3), pp. 341-344.
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ABSTRACT: In this paper the anti-solvency behavior of supercritical carbon dioxide (CO2) as a way to recover an organic compound from an ionic liquid by crystallization is explored. As an example, the conditions for crystallization of the organic compound methyl-(Z)-α-acetamido cinnamate (MAAC) from the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim +][BF4 -]) using supercritical CO2 as anti-solvent are studied experimentally by measuring the phase behavior of the ternary system [bmim+][BF4 -] + CO2 + MAAC. MAAC can be recovered from [bmim+][BF4 -] by either using a shift to higher CO2 concentrations at constant temperature (anti-solvent crystallization) or by using a shift to lower temperatures at constant CO2 concentration (thermal shift). This journal is © The Royal Society of Chemistry.
Bouchard, A., Jovanović, N., Hofland, G.W., Jiskoot, W., Mendes, E., Crommelin, D.J.A., Witkamp, G.-J.
Supercritical fluid drying of carbohydrates: Selection of suitable excipients and process conditions
(2008) European Journal of Pharmaceutics and Biopharmaceutics, 68 (3), pp. 781-794.
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ABSTRACT: The processibility of 15 carbohydrates, more or less commonly used, was investigated as excipients in supercritical fluid drying. The focus was on the ability to produce amorphous powder, the stability of the powders towards crystallisation, and the residual water and ethanol content. The aqueous solutions were sprayed into a pressurised carbon dioxide-ethanol mixture flowing cocurrently through a coaxial two-fluid nozzle. The powder characteristics appeared to be influenced by the supersaturation level reached during the SCF-drying process and by the properties of the sugar species, such as water solubility and glass transition temperature, or the solution viscosities. The stability and the residual solvent content of a selected set of sugars and some mixtures were further analysed. The stability of amorphous powders was investigated at 4 °C, room temperature, 40 and 50 °C. Lactose, maltose, trehalose, raffinose, cyclodextrin, low-molecular-weight dextran and inulin could form free-flowing powders that remained amorphous during the 3-month stability study. Sucrose had to be mixed with other sugars to form a stable amorphous powder. Ethanol could be entrapped in supercritical fluid dried low-molecular-weight sugars, whereas polysaccharide powders were free of ethanol. Measures to prevent or overcome the presence of ethanol are discussed. © 2007 Elsevier B.V. All rights reserved.
Jovanović, N., Bouchard, A., Hofland, G.W., Witkamp, G.-J., Crommelin, D.J.A., Jiskoot, W.
Stabilization of IgG by supercritical fluid drying: Optimization of formulation and process parameters
(2008) European Journal of Pharmaceutics and Biopharmaceutics, 68 (2), pp. 183-190.
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ABSTRACT: The aim of this study was to stabilize human serum immunoglobulin G (IgG) by a supercritical fluid (SCF) drying process. Solutions containing IgG (20 mg/ml) and trehalose or hydroxypropyl-β-cyclodextrin in a 1:4 (w/w) ratio were sprayed into a SCF phase consisting of CO2 and ethanol at 100 bar and 37 °C. Initially, a set of drying conditions previously developed to successfully stabilize lysozyme and myogobin formulations was used [N. Jovanović, A. Bouchard, G.W. Hofland, G.J. Witkamp, D.J.A. Crommelin, W. Jiskoot, Eur. J. Pharm. Sci. 27 (2006) 336-345]. Dried formulations were analyzed by Karl Fisher titration, scanning electron microscopy, X-ray powder diffraction, and modulated DSC. Protein structure in the solid-state was studied by FTIR and after reconstitution by UV/Vis, circular dichroism and fluorescence spectroscopy, GPC and SDS-PAGE. When IgG was dried under the above-mentioned conditions, substantial amounts of insoluble aggregates were formed. Addition of buffer helped to reduce the fraction of insoluble material but not of soluble aggregates. Full stabilization could be achieved by adjusting the process conditions: drying without ethanol while keeping the other conditions the same, or drying with ethanol at a temperature below the critical point (20 °C). In conclusion, it is possible to stabilize human IgG by SCF drying provided that the formulation and process conditions are tailored to meet the specific requirements of the protein. © 2007 Elsevier B.V. All rights reserved.
Jovanović, N., Bouchard, A., Sutter, M., Van Speybroeck, M., Hofland, G.W., Witkamp, G.-J., Crommelin, D.J.A., Jiskoot, W.
Stable sugar-based protein formulations by supercritical fluid drying
(2008) International Journal of Pharmaceutics, 346 (1-2), pp. 102-108.
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ABSTRACT: The aim of this work was to produce stable, sugar-containing protein formulations by supercritical fluid (SCF) drying. Lysozyme solutions with and without added sucrose or trehalose were dried by spraying them in an SCF composed of CO2 and ethanol or CO2 only. The protein-to-sugar ratio was varied between 1:0 and 1:10 (w/w). Dried formulations were stored at 4 °C for three months and analyzed by Karl Fischer titration, scanning electron microscopy, X-ray powder diffraction, differential scanning calorimetry and Fourier transform infrared spectroscopy. Lysozyme stability after reconstitution was determined by an enzymatic activity assay, UV/Vis spectroscopy, and SDS-PAGE. Smooth, spherical particles of 1-25 μm size were obtained. All formulations were initially amorphous. Crystallization during storage only occurred with a protein-to-sugar ratio of 1:10 and could be avoided by performing SCF drying without ethanol. Absence of residual ethanol in dried trehalose formulations increased the glass transition temperature up to 120 °C. Lysozyme in dried formulations was structurally stable, with exception of the 1:0 and 1:1 protein-to-sugar ratios, where reversible protein aggregation occurred. The results show that by avoiding ethanol, which up to now has been considered mandatory for efficient drying of aqueous solutions, and by choosing the proper protein-to-sugar ratio, it is possible to obtain stable, sugar-based protein formulations through SCF drying. © 2007 Elsevier B.V. All rights reserved.
Breure, B., Bottini, S.B., Witkamp, G.-J., Peters, C.J.
Thermodynamic modeling of the phase behavior of binary systems of ionic liquids and carbon dioxide with the group contribution equation of state
(2007) Journal of Physical Chemistry B, 111 (51), pp. 14265-14270.
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ABSTRACT: The group contribution equation of state (GC-EOS) was applied to predict the phase behavior of binary systems of ionic liquids of the homologous families 1-alkyl-3-methylimidazolium hexafluorophosphate and tetrafluoroborate with CO2. Pure group parameters for the new ionic liquid functional groups [-mim] [PF6] and [-mim] [BF4] and interaction parameters between these groups and the paraffin (CH3, CH2) and CO2 groups were estimated. The GC-EOS extended with the new parameters was applied to predict high-pressure phase equilibria in binary mixtures of the ionic liquids [emim][PF6], [bmim][PF6], [hmim][PF6], [bmim][BF4], [hmim][BF4], and [omim][BF4] with CO2. The agreement between experimental and predicted bubble point data for the ionic liquids was excellent for pressures up to 20 MPa, and even for pressures up to about 100 MPa, the agreement was good. The results show the capability of the GC-EOS to describe phase equilibria of systems consisting of ionic liquids. © 2007 American Chemical Society.
Golubovic, M., Van Hateren, S.H., Ottens, M., Witkamp, G.J., Van Der Wielen, L.A.M.
A method for lipase co-precipitation in a biodegradable protein matrix
(2007) Biotechnology and Bioengineering, 98 (6), pp. 1209-1218.
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ABSTRACT: This article presents a novel method for immobilization of active ingredients. The method is based on CO2 aided active ingredient co-precipitation with glycinin, a biodegradable protein matrix from edible soybean protein. Glycinin precipitates abundantly under isoelectric conditions and serves as the matrix within which the active substance is trapped during the precipitation process. The enzyme lipase from Candida rugosa was successfully co-precipitated into the protein pellet to prove the principle. It was shown that the lipase within the co-precipitate retained lipase and esterase activity under different pH conditions. In some cases the activity was even higher than the activity of crude lipase, possibly due to the protective role of the matrix protein. Due to the retained lipase activity and food-grade quality of the binary precipitate, it has potential of being used in the food or pharmaceutical industry. Additional quality of the binary precipitate is the potentially significantly reduced downstream processing due to the fact that no organic solvents or precipitants were used in the precipitation process. © 2007 Wiley Periodicals, Inc.
Kroon, M.C., Buijs, W., Peters, C.J., Witkamp, G.-J.
Quantum chemical aided prediction of the thermal decomposition mechanisms and temperatures of ionic liquids
(2007) Thermochimica Acta, 465 (1-2), pp. 40-47.
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ABSTRACT: The long-term thermal stability of ionic liquids is of utmost importance for their industrial application. Although the thermal decomposition temperatures of various ionic liquids have been measured previously, experimental data on the thermal decomposition mechanisms and kinetics are scarce. It is desirable to develop quantitative chemical tools that can predict thermal decomposition mechanisms and temperatures (kinetics) of ionic liquids. In this work ab initio quantum chemical calculations (DFT-B3LYP) have been used to predict thermal decomposition mechanisms, temperatures and the activation energies of the thermal breakdown reactions. These quantum chemical calculations proved to be an excellent method to predict the thermal stability of various ionic liquids. © 2007.
Genceli, F.E., Lutz, M., Spek, A.L., Witkamp, G.-J.
Crystallization and characterization of a new magnesium sulfate hydrate MgSO4 11H2O
(2007) Crystal Growth and Design, 7 (12), pp. 2460-2466.
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ABSTRACT: The MgSO4 crystal hydrate formed below approximately 0 °C was proven to be the undecahydrate, MgSO4; · 11H2O (meridianiite) instead of the reported dodecahydrate MgSO4 ·12H2O. The crystals were grown from solution by eutectic freeze and by cooling crystallization. The crystal structure analysis and the molecular arrangement of these crystals were determined using single crystal X-ray diffraction (XRD). Reflections were measured at a temperature of 110(2) K. The structure is triclinic with space group Pl̄ (No. 2). The crystal is a colorless block with the following parameters F.W. = 318.55, 0.54 × 0.24 × 0.18 mm3, a = 6.72548(7) Å, b = 6.77937(14) Å, c = 17.2898(5) Å, α = 88.255(1)°, β= 89.478(2)°, γ = 62.598(1)°, V = 699.54(3) Å3, Z = 2, Dcalc = 1.512 g/cm3, μ = 0.343 mm-1. Raman spectroscopy was used for characterizing MgSO4 · 11H2O and for comparing the vibrational spectra with the MgSO4 · 7H 2O salt. Between the two salts, there are significant differences mainly in the type of interactions of water with sulfate groups in the lattice, in view of the different O-H stretching vibrations, as well as sulfate, O - H - O (sulfate) and O - Mg - O bands vibrational modes. Thermogravimetric analysis confirmed the stochiometry of the MgSO4 · 11H2O salt. Additionally, the Miller indices of the major faces of MgSO4 · 11H2O crystals were defined. © 2007 American Chemical Society.
Karakatsani, E.K., Economou, I.G., Kroon, M.C., Peters, C.J., Witkamp, G.-J.
tPC-PSAFT modeling of gas solubility in imidazolium-based ionic liquids
(2007) Journal of Physical Chemistry C, 111 (43), pp. 15487-15492.
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ABSTRACT: The truncated perturbed chain-polar statistical associating fluid theory (tPC-PSAFT) is re-parametrized for imidazolium-based ionic liquids (ILs) by fitting IL density data over a wide temperature range and restricting the model to predict very low vapor pressure values, in agreement with recent experimental evidence. The new set of parameters is used for the correlation of carbon dioxide solubility in various ILs using a binary interaction parameter, k ij. The correlated kij values are much lower than the values used previously for the same mixtures (Kroon et al., J. Phys. Chem. B 2006, 110, 9262). Furthermore, the solubilities of carbon monoxide, oxygen, and trifluoromethane in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim +][PF6 -]) are correlated. In all cases, the agreement between tPC-PSAFT correlation and experimental data for mixtures is very good. © 2007 American Chemical Society.
Bouchard, A., Hofland, G.W., Witkamp, G.-J.
Properties of sugar, polyol, and polysaccharide water-ethanol solutions
(2007) Journal of Chemical and Engineering Data, 52 (5), pp. 1838-1842.
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ABSTRACT: The solubility and viscosity of sugars (glucose, lactose, leucrose, maltose, raffinose, sucrose, and trehalose), polyols (maltitol, mannitol, sorbitol, and xylitol), and polysaccharides (β-cyclodextrin, dextrans, and inulin) in water and water-ethanol mixtures was investigated at 310 K. The increase in ethanol fraction caused a decrease in solubility in all cases. The viscosity of a 10 % (w/w) solution of any of those sugars was (1 to 1.25) mPa s except dextran solutions, which reached 5 mPa s. The viscosity of saturated solutions varied strongly from one compound to another even though the solubilities were similar. The metastable zone widths of sucrose, maltose, and lactose precipitated with ethanol were significantly larger than the one measured for mannitol. © 2007 American Chemical Society.
Bouchard, A., Hofland, G.W., Witkamp, G.-J.
Solubility of glycine polymorphs and recrystallization of β-glycine
(2007) Journal of Chemical and Engineering Data, 52 (5), pp. 1626-1629.
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ABSTRACT: The solubilities of α-, β-, and y-glycine in aqueous solutions containing methanol, ethanol, 2-propanol, or acetone were measured at 310 K. The solubility of all the polymorphs dropped rapidly as a function of the concentration of antisolvent. The solubility of the glycine polymorphs in water-antisolvent mixtures was, in decreasing order: methanol > ethanol > 2-propanol > acetone. The solubility of α-glycine was slightly higher than that of γ-glycine, but the solubility of β-glycine was significantly higher by up to 17%. The induction time for the recrystallization of β- to α-glycine in those water-antisolvent mixtures was, in decreasing order: methanol > ethanol > acetone > 2-propanol. This signifies that the selection of an antisolvent for preparation of β-glycine can have an important effect on the product. © 2007 American Chemical Society.
Nieborg, V.H.J., Lindken, R., Witkamp, G.J., Kramer, H.J.M., Westerweel, J.
Mixing with EOF for a precipitation reaction
(2007) Papers Presented at the 1st International Conference on Industrial Processes for Nano and Micro Products, pp. 93-102.
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ABSTRACT: Microfluidics is becoming increasingly more interesting for chemical engineering applications. Here a closer look is taken at the possibilities of performing a precipitation reaction in a microfluidic device. This specific type of reaction demands for instance fast mixing. We take sodium chloride precipitation as a model anti-solvent precipitation reaction. Effective mixing is achieved by applying an electric field over the fluid. The dispersion of a plug is measured when it is transported by pressure driven flow or electroosmotic flow. These two different types of transportation are investigated. © BHR Group 2007 Industrial Processes for Nano and Micro Products.
Bouchard, A., Jovanović, N., Hofland, G.W., Mendes, E., Crommelin, D.J.A., Jiskoot, W., Witkamp, G.-J.
Selective production of polymorphs and pseudomorphs using supercritical fluid crystallization from aqueous solutions
(2007) Crystal Growth and Design, 7 (8), pp. 1432-1440.
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ABSTRACT: A number of supercritical fluid technologies are known to enable the selective production of polymorphs, only by changing the process conditions. These techniques use either supercritical CO2 or organics as solvent. In this work, the precipitation of small organic molecules from aqueous solution was studied using a mixture of supercritical CO2 and ethanol as drying medium and as anti-solvent. Glycine, which has three polymorphs, was precipitated by a direct spraying process. By simple manipulation of the flow rates, the process could be tuned to selectively precipitate either pure α- or β-glycine. When increasing the ethanol concentration in the system, the precipitation of the metastable β-glycine was preferred over the precipitation of α-glycine. Small portions of γ-glycine could be found when choosing slow drying conditions. The same process route was applicable to selectively precipitate pseudomorphs as well. Increasing the ethanol concentration in the extractant phase favored the precipitation of phenylalanine anhydrate over the monohydrate form. The study shows that the supercritical fluid crystallization process has significant potential for the selective production of polymorphs and pseudomorphs of water soluble compounds into small particles in a single step. © 2007 American Chemical Society.
Gärtner, R.S., Witkamp, G.-J.
Mixed solvent reactive recrystallization of trona (sodium sesqui-carbonate) into soda (sodium carbonate anhydrate)
(2007) Hydrometallurgy, 88 (1-4), pp. 75-91.
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ABSTRACT: A new conversion process for the production of soda (Na2CO3(s)) from trona (Na2CO3·NaHCO3·2H 2O(s)) and other sodium bicarbonate containing sodium carbonate sources is presented. By using a mixed solvent consisting of ethylene glycol and water, the boiling point of the solution was increased and the stability of trona could be decreased to such a degree, that it spontaneously recrystallized to anhydrous soda (Na2CO3(s)) and wegscheiderite (Na2CO3·3NaHCO3(s)). Additionally, the sodium bicarbonate content could be completely decomposed thermally in the mixed solvent into sodium carbonate, which crystallized as stable, pure anhydrous soda. Fundamental mechanisms of this process are discussed: The stability of trona as a function of mixed solvent composition, water activity and temperature is reported. The dissolution rate, the bicarbonate decomposition rate as well as the (pseudo) solid phase conversion rate of trona were investigated as functions of mixed solvent composition and temperature. It was found that beyond a certain temperature, depending on the mixed solvent composition, the trona would convert via the (pseudo) solid state. © 2007 Elsevier B.V. All rights reserved.
Van Der Kraan, M., Cid, M.V.F., Woerlee, G.F., Veugelers, W.J.T., Witkamp, G.-J.
Equilibrium study on the disperse dyeing of polyester textile in supercritical carbon dioxide
(2007) Textile Research Journal, 77 (8), pp. 550-558.
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ABSTRACT: The dyeing of polyester textile in supercritical carbon dioxide (scCO2) was investigated experimentally. The influence of temperature and density of the scCO2 on the process was studied in the ranges 85-125°C and 400-550 kg/m3. The dye saturation concentration in the polyester increased and the distribution coefficient decreased with temperature, the latter showing a logarithmic dependence on the reciprocal of temperature. Increasing the fluid density led to an increasing saturation concentration and a decreasing distribution coefficient. When the right temperature and solvent density were chosen for the supercritical process, the same dye concentration could be attained as in aqueous dyeing. It was found that the adsorption of the dye on the polyester followed Nernst adsorption, as is the case in aqueous dyeing. The experiments showed that the dyeing was exothermic, with a negative change of entropy. The thermodynamic characteristics of supercritical and aqueous dyeing were concluded to be roughly the same, with similar saturation concentrations, thermodynamic affinities and heats and entropies of dyeing. © SAGE Publications, Inc. 2007.
Huijgen, W.J.J., Comans, R.N.J., Witkamp, G.-J.
Cost evaluation of CO2 sequestration by aqueous mineral carbonation
(2007) Energy Conversion and Management, 48 (7), pp. 1923-1935.
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ABSTRACT: A cost evaluation of CO2 sequestration by aqueous mineral carbonation has been made using either wollastonite (CaSiO3) or steel slag as feedstock. First, the process was simulated to determine the properties of the streams as well as the power and heat consumption of the process equipment. Second, a basic design was made for the major process equipment, and total investment costs were estimated with the help of the publicly available literature and a factorial cost estimation method. Finally, the sequestration costs were determined on the basis of the depreciation of investments and variable and fixed operating costs. Estimated costs are 102 and 77 €/ton CO2 net avoided for wollastonite and steel slag, respectively. For wollastonite, the major costs are associated with the feedstock and the electricity consumption for grinding and compression (54 and 26 €/ton CO2 avoided, respectively). A sensitivity analysis showed that additional influential parameters in the sequestration costs include the liquid-to-solid ratio in the carbonation reactor and the possible value of the carbonated product. The sequestration costs for steel slag are significantly lower due to the absence of costs for the feedstock. Although various options for potential cost reduction have been identified, CO2 sequestration by current aqueous carbonation processes seems expensive relative to other CO2 storage technologies. The permanent and inherently safe sequestration of CO2 by mineral carbonation may justify higher costs, but further cost reductions are required, particularly in view of (current) prices of CO2 emission rights. Niche applications of mineral carbonation with a solid residue such as steel slag as feedstock and/or a useful carbonated product hold the best prospects for an economically feasible CO2 sequestration process. © 2007 Elsevier Ltd. All rights reserved.
Fernandez Cid, M.V., Buijs, W., Witkamp, G.-J.
Application of molecular modeling in the optimization of reactive cotton dyeing in supercritical carbon dioxide
(2007) Industrial and Engineering Chemistry Research, 46 (12), pp. 3941-3944.
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ABSTRACT: Reactive dyeing of cotton in supercritical carbon dioxide is a green alternative to reduce water consumption and wastewater. Cotton could be successfully dyed and the reaction kinetics was determined; however, several issues need to be clarified for further optimization of the dyeing process. For instance, it was observed that the difluorotriazine dye reacted very fast with cotton but its kinetics showed a negative activation energy. Furthermore, it seemed that fixation was strongly related to the nature of cosolvents methanol and dimethyl sulfoxide. Finally, the dihalogenotriazine dye reacted selectively with cotton in the presence of methanol, commonly used as a model for cotton. A molecular modeling approach was applied to provide explanations for the above-mentioned experimental phenomena. In combination with experimental data, molecular modeling was shown to be a powerful tool for the understanding and optimization of the process of cotton dyeing in supercritical carbon dioxide. © 2007 American Chemical Society.
Martín, A., Bouchard, A., Hofland, G.W., Witkamp, G.-J., Cocero, M.J.
Mathematical modeling of the mass transfer from aqueous solutions in a supercritical fluid during particle formation
(2007) Journal of Supercritical Fluids, 41 (1), pp. 126-137.
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ABSTRACT: A solved mathematical model of the mass transfer between a droplet of water and a gas mixture of supercritical fluid and co-solvent is presented. This model is applicable to the study of the precipitation from drying of aqueous solutions with a supercritical fluid. The model takes into account the two-way mass transfer of water into the gas phase, and of the supercritical fluid and co-solvent into the droplet. The energy balance is also included in the calculations. The resolution of the model allows the determination of the radial profiles of composition and temperature as a function of time, both inside and outside of the droplet, and the variation of the droplet radius with time. The model has been used for the interpretation of experimental results of the precipitation and drying of lysozyme from aqueous solutions with a mixture of supercritical carbon dioxide and ethanol. The phase behavior of the ternary system CO2-water-ethanol was modeled with the Peng-Robinson Equation of State with Wong-Sandler mixing rule, while mass and energy transport properties were calculated with suitable empirical correlations. The calculations show that the droplet undergoes an initial stage of swelling due to the condensation of ethanol, followed by a decrease in the droplet radius after saturation of the droplet with ethanol and CO2 due to the extraction. Since lysozyme is poorly soluble in ethanol and CO2, particle formation may already begin in the initial swelling stage. It was also found that the maximum concentration of ethanol and CO2 in the droplet is strongly dependent on the initial concentration of ethanol in the gas phase. This could explain the variations in particle morphology observed experimentally when the ethanol/CO2 flow ratio is varied. Pressure variations only have a small effect on the time required for the complete evaporation of the droplet. An increase in temperature causes a large variation in the saturation composition of the droplet and enhances the evaporation rate. © 2006 Elsevier B.V. All rights reserved.
van der Kraan, M., Fernandez Cid, M.V., Woerlee, G.F., Veugelers, W.J.T., Peters, C.J., Witkamp, G.J.
Equilibrium distribution of water in the two-phase system supercritical carbon dioxide-textile
(2007) Journal of Supercritical Fluids, 40 (3), pp. 336-343.
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ABSTRACT: When natural fibres are dyed in supercritical carbon dioxide, the addition of a small amount of water increases coloration. For a process design it is important to know how much water has to be added to obtain a desired humidity of both textile and carbon dioxide. In this work a thermodynamic model is proposed to calculate the distribution of water over the textile phase and the supercritical phase as a function of pressure and temperature. The phase equilibrium is described with Raoult's law for non-ideal fluids. The absorbed water in the textile is a condensed phase and is modelled here as a non-ideal liquid, using the NRTL-equation. The non-ideality of the supercritical phase is described by a solubility enhancement factor, a new equation derived from statistical thermodynamics. Although the model is applied to cotton, viscose, silk and wool, it can be used for all water absorbing textiles. © 2006 Elsevier B.V. All rights reserved.
van der Kraan, M., Fernandez Cid, M.V., Woerlee, G.F., Veugelers, W.J.T., Witkamp, G.J.
Dyeing of natural and synthetic textiles in supercritical carbon dioxide with disperse reactive dyes
(2007) Journal of Supercritical Fluids, 40 (3), pp. 470-476.
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ABSTRACT: Polyester, nylon, silk and wool were dyed with disperse reactive dyes in supercritical carbon dioxide (scCO2). The dyes were substituted with either vinylsulphone or dichlorotriazine reactive groups. Since earlier research showed that water, distributed over the scCO2 and the textile, increased the colouration, experiments were done with the vinylsulphone dye with varying amounts of water in the dyeing vessel, to investigate if there is an optimum water concentration. The amounts were such, that no liquid water was present. The maximum colouration was obtained when both the scCO2 and the textiles were saturated with water. At the saturation point, deep colours were obtained with the vinylsulphone dye for polyester, nylon, silk and wool, with fixation percentages between 70 and 92% when the dyeing time was 2 h. The positive effect of water was due to its ability to swell fibres or due to an effect of water on the reactivity of the dye-fibre system. Also the dichlorotriazine dye showed more colouration when the scCO2 was moist. With this dye, experiments were conducted in water-saturated scCO2, varying the pressure from 225 to 278 bar and the temperature from 100 to 116 °C. The colouration of polyester increased with pressure, the results for silk and wool were not sensitive to pressure. Increasing the temperature had no influence on the dyeing of polyester, silk and wool. The fixations on polyester, silk and wool, being between 71 and 97%, were also independent of pressure and temperature. © 2006 Elsevier B.V. All rights reserved.
Van Rens, G.L.M.A., Van Der Woude, R.R., Kos, G.P.A., Kuipers, J., Witkamp, G.J., Stapersma, D.
Proving the possibility of physical removal of particulate matter with the SJAC-technology
(2007) Proceedings of the Institute of Marine Engineering, Science and Technology Part A: Journal of Marine Engineering and Technology, (9), pp. 29-38.
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ABSTRACT: Particulate matter emissions from shipping affect air quality in port areas. Physical removal of particulate matter is difficult due to the small size of particles. In this article the so-called Steam Jet Aerosol Collector (SJAC) is introduced; a novel technique to enlarge particulate matter, facilitating its physical removal. Results are presented from experiments conducted on a pilot-scale test facility. The SJAC-technology shows potential in combination with a cyclone having a maximum number removal efficiency of 33%, as measured with an SMPS and a maximum mass removal efficiency of 24%, as measured with an absolute filter at 110°C (383K). Further system development is however necessary.
Fernandez Cid, M.V., van Spronsen, J., van der Kraan, M., Veugelers, W.J.T., Woerlee, G.F., Witkamp, G.J.
A significant approach to dye cotton in supercritical carbon dioxide with fluorotriazine reactive dyes
(2007) Journal of Supercritical Fluids, 40 (3), pp. 477-484.
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ABSTRACT: A series of fluorotriazine reactive dyes have been synthesized and applied to dye cotton in supercritical carbon dioxide (scCO2) with good dyeing results. The pieces of cotton to be dyed were previously presoaked in a protic solvent and cosolvents were applied during dyeing. The colour strength of the dyeings was evaluated by K/S measurements. The K/S values achieved on cotton dyed were up to 35.8 ± 4.2. Even after the cotton was subjected to a Shoxlet extraction at 358 K for 1 h, a maximum K/S value of 20.2 ± 1.8 was measured. The percentage of dye molecules chemically fixed to the cotton was on average 85%. The excellent reactivity of fluorotriazines allowed a reduction of 3 h on the dyeing time. It is noticeable that a dye concentration of 10% on weight of the fibre (owf) can be applied to dye cotton with fluorotriazines, since no damage of the cotton fibres occurred, as observed for the chlorotriazines at this high dye concentration. Dyes with fluorotriazine as reactive group were found to be the most preferable dyes for dyeing cotton in scCO2, as they were able to exceed the limitation of the reaction with the cotton. © 2006 Elsevier B.V. All rights reserved.
Bouchard, A., Jovanović, N., Jiskoot, W., Mendes, E., Witkamp, G.-J., Crommelin, D.J.A., Hofland, G.W.
Lysozyme particle formation during supercritical fluid drying: Particle morphology and molecular integrity
(2007) Journal of Supercritical Fluids, 40 (2), pp. 293-307.
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ABSTRACT: Studies have shown that diverse types of particles can be obtained when processing aqueous protein solutions into powders by using supercritical fluids, however, without identifying the mechanism behind these variations. Therefore, the particle formation of lysozyme by supercritical fluid drying was more systemically studied by varying the flow rates of protein solution, supercritical carbon dioxide and ethanol, co-currently sprayed through a coaxial nozzle. Three different morphologies were identified: agglomerated nanoparticles, microspheres and irregular microparticles. These morphologies could be related to the process conditions, in particular to the fraction of ethanol in the extraction medium: agglomerated nanoparticles were produced under anti-solvent precipitation conditions; microspheres under water extraction conditions; and microparticles under competitive rates of both mechanisms. A slight increase in intermolecular β-sheets was observed in powders (<5% residual water content) produced under anti-solvent conditions. Nevertheless, the protein integrity was recovered after rehydration. In conclusion, the alcohol fraction in the extractant has shown to influence both the particle morphology and molecular integrity. The selection of ethanol fraction could be especially important when more labile proteins are to be processed using this technique. © 2006 Elsevier B.V. All rights reserved.
Fernandez Cid, M.V., van Spronsen, J., van der Kraan, M., Veugelers, W.J.T., Woerlee, G.F., Witkamp, G.J.
Acid-catalysed methanolysis reaction of non-polar triazinyl reactive dyes in supercritical carbon dioxide
(2007) Journal of Supercritical Fluids, 39 (3), pp. 389-398.
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ABSTRACT: An extensive study of the reaction mechanism of the methanolysis reaction of triazinyl systems of non-polar reactive dyes has been done in a neutral, moderately acidic and strongly acidic medium. In a neutral reaction medium, dichlorotriazines are more reactive than the monochlorotriazines. However, in a moderately acidic medium, as supercritical carbon dioxide, an inversion in the reactivity pattern of monochlorotriazines was observed, which is related to the dye structure. Amines as substituent group attached to the triazinyl ring showed the largest conversion and k values, approaching those values of dichlorotriazine. Protonation of the ring, and stabilization of the positive charge in the triazinyl ring due to the mesomeric effect, explain the reactivity increased of monochlorotriazines. When acids were added to the reaction medium, resulting in an increase of the acid concentration, the reactivity of monochlorotriazinyl dyes was surprisingly much larger than dichlorotriazine; k values increased up to a factor of 54. The largest k was measured for the monochlorotriazinyl dye, S1Cl-NH2, showing a value of 3.0 × 10-3 s-1, while a value of 3.2 × 10-4 s-1 was measured in supercritical carbon dioxide. In a strongly acidic medium, the reactivity of triazinyl reactive dyes is substantially influenced by the basicity of the substituted groups in the reactive group, and in the chromophore. Based on this kinetic study, the dyeing of cotton in supercritical carbon dioxide under acidic conditions seems to be very promising when triazinyl dyes are used. © 2006 Elsevier B.V. All rights reserved.
Fernandez Cid, M.V., Gerstner, K.N., van Spronsen, J., van der Kraan, M., Veugelers, W.J.T., Woerlee, G.F., Witkamp, G.J.
Novel process to enhance the dyeability of cotton in supercritical carbon dioxide
(2007) Textile Research Journal, 77 (1), pp. 38-46.
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ABSTRACT: A new simple method to improve the dyeability of cotton in supercritical carbon dioxide, which does not require any chemical modification of the cotton, is described here. The affinity of the cotton is enhanced through physical interactions between the pretreatment solvent and the cotton structure. Addition of cosolvents and dissolution of the dye greatly improved the coloration and fixation of the cotton. Experiments with different solvents as pretreatment and as cosolvents were performed. Methanol was found to be the best solvent for the pretreatment. Dimethylsulfoxide (DMSO) as cosolvent and dye carrier provided the highest cotton coloration (K/S 15.3), but a fixation of only 2%. An increase in fixation to 62% was achieved when methanol was the cosolvent and the dye carrier. © 2007 Sage Publications.
Huijgen, W.J.J., Ruijg, G.J., Comans, R.N.J., Witkamp, G.-J.
Energy consumption and net CO2 sequestration of aqueous mineral carbonation
(2006) Industrial and Engineering Chemistry Research, 45 (26), pp. 9184-9194.
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ABSTRACT: Aqueous mineral carbonation is a potentially attractive sequestration technology to reduce CO2 emissions. The energy consumption of this technology, however, reduces the net amount of CO2 sequestered. Therefore, the energetic CO2 sequestration efficiency of aqueous mineral carbonation was studied in dependence of various process variables using either wollastonite (CaSiO3) or steel slag as feedstock. For wollastonite, the maximum energetic CO2 sequestration efficiency within the ranges of process conditions studied was 75% at 200°C, 20 bar CO2, and a particle size of <38 μm. The main energy-consuming process steps were the grinding of the feedstock and the compression of the CO2 feed. At these process conditions, a significantly lower efficiency was determined for steel slag (69%), mainly because of the lower Ca content of the feedstock. The CO2 sequestration efficiency might be improved substantially for both types of feedstock by, e.g., reducing the amount of process water applied and further grinding of the feedstock. The calculated energetic efficiencies warrant a further assessment of the (energetic) feasibility of CO2 sequestration by aqueous mineral carbonation on the basis of a pilot-scale process. © 2006 American Chemical Society.
Himawan, C., Witkamp, G.J.
Crystallization kinetics of MgSO4·12H2O from different scales of batch cooling scraped crystallizers
(2006) Crystal Research and Technology, 41 (9), pp. 865-873.
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ABSTRACT: For reliably scaling up of crystallizers, a full kinetic model is required in addition to heat, mass and population balances. A method for extracting nucleation and growth kinetic parameters for scaling-up seeded batch cooling crystallization was developed and demonstrated with a 15 L and in a 115 L scraped crystallizer using MgSO4·12H2O as the model system. The method includes fitting the time resolved measured solute concentration and the crystal size distributions with a dynamic population-based model. The kinetic parameters extracted from the bench-scale crystallizer agree with those obtained from the pilot scale, confirming that they can be employed for design purposes. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
Huijgen, W.J.J., Witkamp, G.-J., Comans, R.N.J.
Mechanisms of aqueous wollastonite carbonation as a possible CO2 sequestration process
(2006) Chemical Engineering Science, 61 (13), pp. 4242-4251.
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ABSTRACT: The mechanisms of aqueous wollastonite carbonation as a possible carbon dioxide sequestration process were investigated experimentally by systematic variation of the reaction temperature, CO2 pressure, particle size, reaction time, liquid to solid ratio and agitation power. The carbonation reaction was observed to occur via the aqueous phase in two steps: (1) Ca leaching from the CaSiO3 matrix and (2) CaCO3 nucleation and growth. Leaching is hindered by a Ca-depleted silicate rim resulting from incongruent Ca-dissolution. Two temperature regimes were identified in the overall carbonation process. At temperatures below an optimum reaction temperature, the overall reaction rate is probably limited by the leaching rate of Ca. At higher temperatures, nucleation and growth of calcium carbonate are probably limiting the conversion, due to a reduced (bi)carbonate activity. The mechanisms for the aqueous carbonation of wollastonite were shown to be similar to those reported previously for an industrial residue and a Mg-silicate. The carbonation of wollastonite proceeds rapidly relative to Mg-silicates, with a maximum conversion in 15 min of 70% at 200 {ring operator} C, 20 bar CO2 partial pressure and particle size of < 38 μ m. The obtained insight in the reaction mechanisms enables the energetic and economic assessment of CO2 sequestration by wollastonite carbonation, which forms an essential next step in its further development. © 2006 Elsevier Ltd. All rights reserved.
Pronk, P., Infante Ferreira, C.A., Witkamp, G.J.
Influence of solute type and concentration on ice scaling in fluidized bed ice crystallizers
(2006) Chemical Engineering Science, 61 (13), pp. 4354-4362.
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ABSTRACT: During crystallization of ice from aqueous solutions, ice crystals exhibit a marked tendency to adhere to the cooled heat exchanger wall resulting in the formation of an insulating ice layer, often referred to as ice scaling. A promising method to avoid ice scaling is the application of a solid-liquid fluidized bed heat exchanger in which fluidized steel particles remove the ice crystals from the walls. This paper presents experiments with a single-tube fluidized bed heat exchanger in which ice crystals were produced from aqueous solutions of various solutes with varying concentrations. The experiments reveal that ice scaling is only prevented when a certain temperature difference between wall and solution is not exceeded. This transition temperature difference appears to increase approximately linearly with the solute concentration and is higher in aqueous solutions with low diffusion coefficients. The observed phenomena are explained by the hypothesis that ice scaling is only prevented when the mass transfer controlled growth rate of ice crystals on the wall does not exceed the scale removal rate induced by the fluidized steel particles. In conclusion, a model based on these physical phenomena is proposed to predict ice scaling in fluidized bed heat exchangers. © 2006 Elsevier Ltd. All rights reserved.
Himawan, C., Kramer, H.J.M., Witkamp, G.J.
Study on the recovery of purified MgSO4·7H2O crystals from industrial solution by eutectic freezing
(2006) Separation and Purification Technology, 50 (2), pp. 240-248.
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ABSTRACT: Eutectic freezing, characterized by a simultaneous crystallization of ice and salt, was applied to recover magnesium sulphate heptahydrate from a magnesium sulphate industrial stream emitted from flue gas desulphurization. Key aspects of the recovery process for further pilot-scale investigation were studied in a laboratory-scale batch crystallizer with focus on discovering the type of the hydrate product and the quality of the ice and salt crystals. MgSO4·12H2O was formed in the crystallizer and the recrystallization into magnesium sulphate heptahydrate (MgSO4·7H2O) occurred spontaneously during the subsequent filtration and drying above 0.4 °C. The ice and salt crystal products were reasonably pure (only a small amount of Mn was built into the heptahydrate crystals). Ice crystals were disk-shaped with an average size of 300 μm. The MgSO4·7H2O crystals were rather needle-like with an average size of 275 μm. Both products were easily filtered. The characteristics of the eutectic freezing process, i.e. the working area and the dynamics of the simultaneous crystallization, are demonstrated experimentally. © 2005.
Kroon, M.C., Karakatsani, E.K., Economou, I.G., Witkamp, G.-J., Peters, C.J.
Modeling of the carbon dioxide solubility in imidazolium-based ionic liquids with the tPC-PSAFT equation of state
(2006) Journal of Physical Chemistry B, 110 (18), pp. 9262-9269.
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ABSTRACT: In this work, an equation of state (EoS) is developed to predict accurately the phase behavior of ionic liquid + CO2 systems based on the truncated perturbed chain polar statistical associating fluid theory (tPC-PSAFT) EoS. This EoS accounts explicitly for the dipolar interactions between ionic liquid molecules, the quadrupolar interactions between CO2 molecules, and the Lewis acid-base type of association between the ionic liquid and the CO2 molecules. Physically meaningful model pure-component parameters for ionic liquids are estimated based on literature data. All experimental vapor-liquid equilibrium data are correlated with a single linearly temperature-dependent binary interaction parameter. The ability of the model to describe accurately carbon dioxide solubility in various 1-alkyl-3- methylimidazolium-based ionic liquids with different alkyl chain lengths and different anions at pressures from 0 to 100 MPa and carbon dioxide fractions from 0 to 75 mol % is demonstrated. In all cases, good agreement with experimental data is obtained. © 2006 American Chemical Society.
Kroon, M.C., Buijs, W., Peters, C.J., Witkamp, G.-J.
Decomposition of ionic liquids in electrochemical processing
(2006) Green Chemistry, 8 (3), pp. 241-245.
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ABSTRACT: The stability of ionic liquids with respect to high voltage differences is important for their use in electrochemical applications. Ionic liquids decompose when voltage differences larger than their electrochemical window (4-6 V) are applied. However, little is known about the decomposition mechanism and products. In this work the electrochemical breakdown of the ionic liquids 1,1-butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide and 1-butyl-3-methylimidazolium tetrafluoroborate on the cathode is predicted using quantum chemical calculations and validated by experiments. The quantum chemical calculations showed to be an excellent method to predict the electrochemical decomposition reactions and products. © The Royal Society of Chemistry 2006.
Kühne, E., Peters, C.J., Van Spronsen, J., Witkamp, G.-J.
Solubility of carbon dioxide in systems with [bmim][BF4] and some selected organic compounds of interest for the pharmaceutical industry
(2006) Green Chemistry, 8 (3), pp. 287-291.
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ABSTRACT: This work presents phase equilibrium data of the ternary system CO 2 + [bmim][BF4] + solute. Three different organic compounds were studied as the solute in the ternary system: 1-methyl-3- phenylpiperazine (MPhPz), 2-chloro-nicotinonitrile (NtN) and 2-(4-methyl-2-phenyl-1-piperazinyl)-3-pyridinecarbonitrile (PCN). Experiments were carried out in a pressure and temperature range of 1-14 MPa and 343.15-443.15 K, respectively. Samples were prepared with CO2 molar fractions of 0.10 until 0.40 for the system with NtN as the solute, and 0.20 for the other two systems for comparison. The data collected show how the various solutes affect the phase behavior of the binary system CO2 + [bmim][BF4], and at which conditions homogeneous phase can be obtained. © The Royal Society of Chemistry 2006.
Kroon, M.C., Van Spronsen, J., Peters, C.J., Sheldon, R.A., Witkamp, G.-J.
Recovery of pure products from ionic liquids using supercritical carbon dioxide as a co-solvent in extractions or as an anti-solvent in precipitations
(2006) Green Chemistry, 8 (3), pp. 246-249.
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ABSTRACT: In this paper two advanced methods for separation and purification of products from ionic liquids by using supercritical carbon dioxide as a co-solvent in extractions or as an anti-solvent in precipitations are demonstrated. As an example, the recovery of the product N-acetyl-(S)- phenylalanine methyl ester (APAM) from the ionic liquid 1-butyl-3- methylimidazolium tetrafluoroborate ([bmim][BF4]) was studied experimentally. APAM is the product of the asymmetric hydrogenation of methyl-(Z)-α-acetamidocinnamate (MAAC). For extraction of the product, the solubility of APAM in CO2 should be sufficiently high. This solubility is 1.78 g kg-1 at 12.0 MPa and 323 K, whereas [bmim][BF4] has a negligible solubility in scCO2. The extracted product was found to contain no detectible amount of ionic liquid. The solubility of the reactant MAAC in scCO2 is five times lower than the solubility of APAM, which means that a selectivity towards extraction of APAM exists. The product APAM was also precipitated out of the ionic liquid phase using scCO2 as an anti-solvent, enabled by the lower solubility of APAM in ionic liquid/scCO2 mixtures compared to the solubility in the pure ionic liquid at atmospheric conditions (650 g l-1). For example, the solubility of APAM in ionic liquid + scCO2 (1:1.34 g g-1) at 313 K and 18.0 MPa is 162 g l-1. After precipitation the formed crystals can be washed using CO2 to obtain pure product. © The Royal Society of Chemistry 2006.
Jovanović, N., Bouchard, A., Hofland, G.W., Witkamp, G.-J., Crommelin, D.J.A., Jiskoot, W.
Distinct effects of sucrose and trehalose on protein stability during supercritical fluid drying and freeze-drying
(2006) European Journal of Pharmaceutical Sciences, 27 (4), pp. 336-345.
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ABSTRACT: Supercritical fluid (SCF) drying has been proposed as an alternative for freeze-drying to stabilize proteins. Here we studied the influence of sucrose and trehalose during SCF drying on the protein stability and the physical powder characteristics of lysozyme and myoglobin formulations. The results obtained with SCF drying were compared with the results after freeze-drying of the same solutions. Aqueous protein solutions, with or without sugar, were sprayed into a SCF mixture of carbon dioxide and ethanol. The dried products were analyzed by residual water measurements, scanning electron microscopy, X-ray powder diffraction and differential scanning calorimetry. After reconstitution the protein structure was studied by UV/VIS, circular dichroism and fluorescence spectroscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and bioactivity assay (lysozyme). The SCF dried and freeze-dried formulations showed comparable water contents, but their physical properties were substantially different. All freeze-dried cakes were amorphous with fully preserved protein structure. SCF dried sucrose-containing formulations showed agglomerated crystalline particles, whereas SCF dried trehalose-containing formulations appeared to consist of amorphous spherical particles. Particle morphology of excipients-free proteins was protein specific. Nearly all SCF dried lysozyme could be readily reconstituted, but for myoglobin significant fractions of SCF protein did not dissolve, especially in the absence of sugars. Covalent aggregation was not observed for the two proteins. For the recovered soluble fractions, the secondary protein structure was preserved. The tertiary structure was preserved for lysozyme, but not entirely for myoglobin. Surprisingly, during SCF drying trehalose was less protective than sucrose for myoglobin. © 2005 Elsevier B.V. All rights reserved.
Pérez De Diego, Y., Pellikaan, H.C., Wubbolts, F.E., Borchard, G., Witkamp, G.J., Jansens, P.J.
Opening new operating windows for polymer and protein micronisation using the PCA process
(2006) Journal of Supercritical Fluids, 36 (3), pp. 216-224.
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ABSTRACT: To avoid the existing limitations of the PCA process for the precipitation of proteins and polar polymers a new approach based on the use of water to modify the phase behaviour of the system DMSO-CO2 was developed. The addition of water to the DMSO displaces the mixture critical pressure of the solution-CO2 system to higher pressures and produces a new operating region in which the PCA process can be carried out. Following this approach, it was possible to develop a process to produce 1-10 μm particles of N-trimethylchitosan chloride (TMC) suitable for inhalation. Encapsulation of proteins in TMC using this technique could also be successfully achieved. © 2005 Elsevier B.V. All rights reserved.
Huijgen, W.J.J., Witkamp, G.-J., Comans, R.N.J.
Mineral CO2 sequestration by steel slag carbonation
(2005) Environmental Science and Technology, 39 (24), pp. 9676-9682.
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ABSTRACT: Mineral CO2 sequestration, i.e., carbonation of alkaline silicate Ca/Mg minerals, analogous to natural weathering processes, is a possible technology for the reduction of carbon dioxide emissions to the atmosphere. In this paper, alkaline Ca-rich industrial residues are presented as a possible feedstock for mineral CO2 sequestration. These materials are cheap, available near large point sources of CO2, and tend to react relatively rapidly with CO2 due to their chemical instability. Ground steel slag was carbonated in aqueous suspensions to study its reaction mechanisms. Process variables, such as particle size, temperature, carbon dioxide pressure, and reaction time, were systematically varied, and their influence on the carbonation rate was investigated. The maximum carbonation degree reached was 74% of the Ca content in 30 min at 19 bar CO2 pressure, 100 °C, and a particle size of <38 μm. The two most important factors determining the reaction rate are particle size (<2 mm to <38 μm) and reaction temperature (25-225 °C). The carbonation reaction was found to occur in two steps: (1) leaching of calcium from the steel slag particles into the solution; (2) precipitation of calcite on the surface of these particles. The first step and, more in particular, the diffusion of calcium through the solid matrix toward the surface appeared to be the rate-determining reaction step. The Ca diffusion was found to be hindered by the formation of a CaCO3-coating and a Ca-depleted silicate zone during the carbonation process. Research on further enhancement of the reaction rate, which would contribute to the development of a cost-effective CO 2-sequestration process, should focus particularly on this mechanism. © 2005 American Chemical Society.
Genceli, F.E., Gärtner, R.S., Trambitas, D., Rodriguez, M., Witkamp, G.J.
A sustainable technology: Eutectic freeze crystallization - From batch laboratory to continuous industry applications
(2005) Sustainable (Bio)Chemical Process Technology - Incorporating the 6th Intenational Conference on Process Intensification, pp. 235-242.
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ABSTRACT: Eutectic Freeze Crystallization (EFC) offers a technically and economically attractive alternative for conventional separation techniques for the recovery of dissolved salts. EFC operates around the eutectic temperature and composition of aqueous solutions, but can treat a wide variety of feed solutions. Both highly pure salt and ice crystals can be simultaneously obtained as valuable products. Theoretically 100% yield and up to 70% energy cost saving (typically 50%) can be achieved compared to triple stage evaporative crystallization. Separation of ice and salt products takes place inside the crystallizer, based on their density difference. EFC is discussed in terms of its state of the art (from 10-liters lab-scale to 250-liter industrial scale), economical evaluation (compared to triple-stage evaporation and cooling crystallization), product qualities (crystal sizes and impurity contents) and industrial applications. A complete mobile, skid mounted pilot unit for EFC applications was designed and constructed together with industrial partners, allowing the system to be easily installed and connected to an industrial plant. As a practical application, the skid mounted unit was designed for producing 130 ton/year MgSO47H2O salt with a crystallizer volume of 250-liters, and 6.83 m2/m3 cooling surface area. The particle sizes of MgSO412H2O(s) and ice crystals range from 150 to 300 μm. MgSO4.12H2O(s) is not stable above 0°C, at ambient temperature it transforms into MgSO4.7H 2O(s). The impurities in the ice are almost exclusively due to adhering liquor; the ice crystals are in general extremely pure. Washing the ice twice brings its impurity level of Mg2+ and SO4 2- to 10 and 45 ppm respectively, which makes it suitable for use as process water. The impurity level in the MgSO4.7H20 salt is below the detection limit after two times washings (≪ 1 ppm). The recovery of magnesium sulphate as hydrates from washing liquid from ex-flue gas desulphurization has payback times for conventional cooling crystallization of 5.2, for three-stage evaporative crystallization 2.7 and for EFC 2.4 years. © BHR Group 2005 Process Intensification 6.
Kroon, M.C., Peters, C.J., Sheldon, R.A., Van Spronsen, J., Witkamp, G.-J.
Economical and ecological attractiveness of using ionic liquids as combined reaction and separation media
(2005) Sustainable (Bio)Chemical Process Technology - Incorporating the 6th Intenational Conference on Process Intensification, pp. 9-16.
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ABSTRACT: The attractiveness of using ionic liquids as reaction and separation media in the asymmetric hydrogenation of methyl-(Z)-aα-acetamidocinnamate (MAAC), yielding N-acetyl-(S)-phenylalanine methyl ester (APAM), is quantified. Compared to the conventional process the costs for catalyst make-up (€ 5. 50 versus 0 per kg APAM), solvent make-up (€ 0.63 versus € 0 per kg APAM) and energy costs (€ 0.48 versus € 0.13 per kg APAM) in the novel process are lower. The novel process using ionic liquids is economically as well as environmentally favorable. © BHR Group 2005 Process Intensification 6.
Huijgen, W., Witkamp, G.-J., Comans, R.
Mineral CO2 sequestration in alkaline solid residues
(2005) Greenhouse Gas Control Technologies, pp. 2415-2418.
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ABSTRACT: CO2 sequestration by mineral carbonation has been recognized as a promising route for the permanent and safe storage of carbon dioxide. Various process routes have been proposed. As feedstock, calcium or magnesium containing primary minerals are used. In addition to calcium- or magnesium-containing primary minerals, suitable alkaline solid residues can be used as feedstock. The use of alkaline residues has several advantages, such as their availability close to CO2 sources and their higher reactivity for carbonation than primary minerals. In addition, the environmental quality of residues can potentially be improved by carbonation. In this study, key factors of the mineral CO2 sequestration process are identified, their influence on the carbonation process is examined, and environmental properties of the reaction products with regard to their possible beneficial utilization are investigated. The use of alkaline solid residues forms a potentially attractive alternative for the first mineral sequestration plants. A possibly attractive alternative is the use of suitable alkaline solid residues, such as ashes from waste incineration, demolition waste and slags from steel production. © 2005 Elsevier Ltd. All rights reserved.
Gärtner, R.S., Witkamp, G.-J.
Regeneration of mixed solvent by ion exchange resin: Selective removal of chloride and sulfate
(2005) Separation Science and Technology, 40 (12), pp. 2391-2410.
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ABSTRACT: The selective extraction of sulfate and chloride ions from mixed solvent solutions was investigated. The mixed solvents consisted of water and 50 to 100%-w (salt-free solvent) ethylene glycol. The extraction was measured for mixed solvent solutions containing only sulfate and chloride, and mixed solvent solutions saturated with trona (sodium sesquicarbonate, Na2CO 3 · NaHCO3 · 2H2O(s). Three anion exchange resins, Dowex 1X8-50, Dowex 21K-Cl, and Dowex MSA-1, were investigated for their chemical and physical resistance to the mixed solvent carbonate/bicarbonate solutions, for their swelling behavior in the different mixed solvents, and for their extraction efficiency for chloride and sulfate. The loading of the ion exchangers was fitted to a Langmuir-type sorption model. While the extraction from trona-free mixed solvents was well reproduced, the loading of the ion exchangers with chloride and sulfate from trona-saturated mixed solvent solutions did not fit the sorption model. It appears, rather, that under these conditions chloride and sulfate are "salted out" of the bulk solution and driven into the ion exchangers. Copyright © Taylor & Francis, Inc.
Pronk, P., Ferreira, C.A.I., Witkamp, G.J.
ICE scaling prevention with a fluidized bed heat exchanger
(2005) VDI Berichte, (1901 II), art. no. D-14, pp. 849-854.
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ABSTRACT: In most ice crystallization processes, scraped surface heat exchangers are applied to prevent ice scaling, but these apparatuses have disadvantages such as high investment and maintenance costs, especially for large-scale applications. An interesting alternative is a fluidized bed heat exchanger in which fluidized steel particles prevent ice scaling. This paper presents results from ice crystallization experiments with a single-tube fluidized bed heat exchanger. During the experiments, ice crystals were formed in aqueous solutions of different solutes with varying concentrations. The experiments revealed that ice scaling was only prevented when a certain temperature difference between wall and solution was not exceeded. This maximum temperature difference appeared to increase linearly with the solute concentration and was higher in aqueous solutions with low diffusion coefficients. The observed phenomena are explained by the hypothesis that ice scaling is only prevented when the crystal growth rate of ice crystals on the wall does not exceed the scale removal rate induced by the fluidized steel particles.
Gärtner, R.S., Witkamp, G.-J.
Mixed solvent recrystallization for the densification and purification of soda ash
(2005) VDI Berichte, (1901 I), art. no. B-31, pp. 459-464.
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ABSTRACT: Soda, sold as light or dense soda ash, is an important bulk chemical and produced annually on a scale of several million short tons world-wide. At atmospheric conditions, soda (sodium carbonate anhydrate) does not form from its aqueous solution, as only hydrates are stable. In a mixed solvent solution, composed of an organic antisolvent (ethylene glycol) and water, the anhydrate is stable and can be crystallized by evaporative crystallization or more energy-efficiently by a double recrystallization process. Since crystallization is a highly selective separation process and since the soda is grown under controlled conditions in the mixed solvent solution, a significant purification effect was expected. The purifying effect of the double recrystallization (light soda to monohydrate, monohydrate to dense soda) was studied in this work. The effect of anionic impurities, which commonly occur in current soda production processes, was investigated: Sulfate, borate, chloride and fluoride. It was found that fluoride, chloride and borate were only incorporated in ppm levels in the solid, while sulfate was incorporated almost quantitatively.
Genceli, F.E., Trambitas, D.O., Gärtner, R.S., Rodriguez, M., Witkamp, G.J.
3rd generation cooled disk column crystallizer and a skid mounted unit for eutectic freeze crystallization
(2005) VDI Berichte, (1901 II), art. no. D-15, pp. 855-860.
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ABSTRACT: Soluble inorganic salts from industrial processes and aqueous waste streams can be recovered by Eutectic Freeze Crystallization (EFC). Around the eutectic temperature both highly pure salt and ice crystals can be simultaneously recovered as valuable products. In this work, the third generation Cooled Disc Column Crystallizer (CDCC-3) is presented. It has a capacity of 250-liters, 7 compartments and 6.72 m2/m3 cooling surface area. Compared to previous designs [Ham99, Vae02, Ham03, Vae03, Gen05], the CDCC-3 has more effective heat flux, a further optimized crystallizer geometry for gravitational separation, and an optimum residence time for nucleation and growth of both ice and salt crystals in continuous operation has been determined. A complete mobile (skid mounted) pilot unit for industrial applications was designed and constructed, allowing the system to be easily installed and integrated into an industrial plant. The unit consists of the CDCC-3, belt filtration, wash column, separation and storage tanks and special measurement devices (image analysis, data acquisition and a field bus based control system). As a practical application, the skid mounted unit was designed for producing 40 ton/year MgSO4·7H2O salt. The CDCC-3 is designed to obtain a production rate (in kg per second per cubic meter of the main crystallizer body) of 0.016 kg.s-1.m-3 for ice and for MgSO 4·12H2O salt. Besides process flow diagrams, the practical performances of the CDCC-3 in terms of heat transfer properties, optimal gravity separation, efficiency of ice scale removal from the cooled surfaces, nucleation and growth kinetics and particle sizes of salt and ice crystals are presented.
Bouchard, A., Jovanović, N., Crommelin, D.J.A., Jiskoot, W., Hofland, G.W., Witkamp, G.-J.
Crystallisation behaviour of sugars precipitated by supercritical fluids
(2005) VDI Berichte, (1901 II), art. no. D-9, pp. 817-822.
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ABSTRACT: Aqueous solutions of common saccharides and polyols used by the pharmaceutical industry were spray dried in various concentrations with a co-current flow of supercritical carbon dioxide enriched with ethanol in a pressurised precipitation vessel, while keeping all other process conditions constant. The dry powders were recovered from a filter after pressure release. The residual water content was measured and the particle morphology and crystallinity were observed. Sucrose and mannitol were readily crystallised, but the trehalose was amorphous. The effect of viscosity and of hydrate formation is discussed.
De Diego, Y.P., Pellikaan, H.C., Wubbolts, F.E., Witkamp, G.J., Jansens, P.J.
Operating regimes and mechanism of particle formation during the precipitation of polymers using the PCA process
(2005) Journal of Supercritical Fluids, 35 (2), pp. 147-156.
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ABSTRACT: The vapour-liquid equilibrium phase behavior of a solvent and carbon dioxide provides two different regions of operation for the precipitation with a compressed antisolvent (PCA) process. Below the critical pressure of the mixture there is an interface between the liquid- and vapour-phase. Solution droplets are formed by atomisation in the nozzle. Above the critical- (or saturation-) pressure there is no phase boundary and contact between CO 2 and solution takes place by mixing. Additionally, in both operating regions, droplets of a polymer rich-phase are formed as result of a liquid-liquid phase split induced in the polymer solution when it gets in contact with the CO2. This article provides experimental evidence for the hypothesis that when processing polymer solutions there are two different mechanisms of droplet formation governing the final size of the precipitated polymer particles: hydraulic atomisation and liquid-liquid phase split. The system l-polylactic acid (l-PLA)-dichloromethane (DCM)-CO2 was used to demonstrate that particle size can be manipulated by modifying the operating conditions. Working at conditions below the mixture critical pressure of the solvent-CO2 mixture it was possible to produce polymer particles in the range of 5-50 μm. At conditions where the two fluids are completely miscible, l-PLA particles ranging from 0.1 to 2 μm and microfibers were obtained. The possibility of co-precipitation of cholesterol and l-PLA was also addressed. © 2005 Elsevier B.V. All rights reserved.
Pérez De Diego, Y., Wubbolts, F.E., Witkamp, G.J., De Loos, Th.W., Jansens, P.J.
Measurements of the phase behaviour of the system dextran/DMSO/CO 2 at high pressures
(2005) Journal of Supercritical Fluids, 35 (1), pp. 1-9.
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ABSTRACT: This paper deals with the measurements of the phase behaviour at high pressures of the system dextran/dimethylsulphoxide/CO2, a system that is being used to study the micronisation of biodegradable polymers using the PCA process. The study of the phase behaviour has been performed combining two independent measurement techniques. It will be shown that the variable composition view cell method recently developed [1] is a useful, easy and reliable method that can be applied to study polymer systems. It can be used to determine the amount of CO2 needed to induce a liquid-liquid phase split in the polymer solution within a 1-2 wt.% error. However, this method was not sensitive enough to predict how the studied system reacts to moderate changes in pressure and temperature. The Cailletet tube method was used to obtain more accurate PT data (isopleths) to complete the information on the phase behaviour of the system. The influence on the PT phase behaviour of the concentration of CO2, the concentration of dextran as well as the presence of water in the system was studied. © 2004 Elsevier B.V. All rights reserved.
Fernandez Cid, M.V., Van Spronsen, J., Van Der Kraan, M., Veugelers, W.J.T., Woerlee, G.F., Witkamp, G.J.
Excellent dye fixation on cotton dyed in supercritical carbon dioxide using fluorotriazine reactive dyes
(2005) Green Chemistry, 7 (8), pp. 609-616.
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ABSTRACT: Development of a water-free dyeing process for cotton is essential for the textile industry due to ecological and economical reasons. In this study, a dyeing method is described where cotton has been effectively dyed in supercritical carbon dioxide (scCO2). Excellent dye fixation of 100%, and colour strength (K/S) values up to 30, were achieved in a small batch reactor and in a scale-up vessel. A series of non-polar reactive dyes with fluorotriazine as reactive group were synthesised at our laboratory. Fluorotriazines were found to be the best dyes for dyeing cotton and their reaction with cotton was improved by adding small quantities of acids to the reaction medium. H3PO4 and HAc were tested at different concentrations on cotton dyed with fluorotriazines. Evenly dyed pieces of cotton without any damage to the cotton fibres were observed in all experiments. An important step forward has been made for the future commercialization of a green process for industrially dying cotton in scCO2. Elimination of water and its costly treatment can be now achieved in the cotton dyeing process. © The Royal Society of Chemistry 2005.
Golubovic, M., Van Hateren, S.H., Ottens, M., Witkamp, G.-J., Van Der Wielen, L.A.M.
Novel method for the production of pure glycinin from soybeans
(2005) Journal of Agricultural and Food Chemistry, 53 (13), pp. 5265-5269.
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ABSTRACT: A novel method for the purification of glycinin from soy meal is presented. The method is based on the isoelectric precipitation of glycinin by using carbon dioxide as a volatile precipitant. Gaseous CO2 was pressurized into the protein solution, thus lowering the pH and initiating glycinin precipitation. Pressurization and, consequently, acidification were done in a slow and controlled manner, with the end point of pH 6.4. The acidity of the protein solution was well controlled via the pressure of gaseous CO2. In this way simultaneous precipitation of other soybean proteins was prevented and very pure glycinin was obtained. Approximately 40% of the glycinin present in the protein solution was recovered with purity as high as 98%. The purification process was successfully performed on both small and large scales, without affecting glycinin purity. © 2005 American Chemical Society.
Gärtner, R.S., Seckler, M.M., Witkamp, G.-J.
Reactive recrystallization of sodium bicarbonate
(2005) Industrial and Engineering Chemistry Research, 44 (12), pp. 4272-4283.
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ABSTRACT: The thermal decomposition of sodium bicarbonate, NaHCO3, in mixed solvents composed of ethylene glycol and water was found to occur solution mediated; i.e., bicarbonate ions (HCO3 -) convert in solution to carbonate ions (CO3 2-), carbon dioxide, and water. The equilibrium of this reaction shifts with increasing temperature toward the bicarbonate decomposition. Above 90 °C, the decomposition of the bicarbonate ions in solution results in the conversion (recrystallization) of solid NaHCO3(s) (nahcolite) in contact with the solution. This recrystallization of NaHCO3(s) at temperatures above 90 °C is independent of the water content for the tested mixed solvents. Thus, slurries of solid sodium bicarbonate (NaHCO3(s)) above 90 °C undergo a solution-mediated recrystallization via wegscheiderite (Na2CO 3·3NaHCO3(s))-as an intermediately formed solid phase-to sodium carbonate anhydrate (Na2CO3(s)). The decomposition rates were measured and the kinetics fitted to the most probable mechanism, i.e., first order in concentration of the bicarbonate ion in solution. Additionally, the solubility of nahcolite (NaHCO3(s)) was determined for a range of mixed solvent compositions and temperatures. © 2005 American Chemical Society.
Cid, M.V.F., Van Der Kraan, M., Veugelers, W.J.T., Woerlee, G.F., Van Bekkum, H., Witkamp, G.J.
Base promoted etherification reaction of a non-polar reactive dye and methanol by zeolite KA
(2005) Microporous and Mesoporous Materials, 81 (1-3), pp. 269-276.
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ABSTRACT: An unexpected base promoted etherification reaction of a non-polar 4,6-dichloro-1,3,5-triazine type reactive dye and methanol was observed when methanol was dried over zeolite KA. A dye conversion of 100% was measured after 3 min reaction time at room temperature, while, when methanol was not pre-contacted with zeolite KA the dye conversion was only 31% after 24 h. The rate constants of the two-step consecutive reaction between dye and methanol were calculated in order to determine the accelerating effect. At 293 K, k 1 increased a factor of 3000 and k2 a factor of 26,000 compared to these values observed with undried methanol. It has been found that the ion-exchange properties of the zeolite KA are responsible for the base promoted reaction. Elemental analyses of the zeolite KA, pellets and powder, and methanol extracts showed an exchange of cations between the two phases. In the case of pellets the binder material contributes to the cation content of the methanol. The potential of zeolite KA as a base promoter is discussed. © 2005 Elsevier Inc. All rights reserved.
Van Der Kraan, M., Peeters, M.M.W., Fernandez Cid, M.V., Woerlee, G.F., Veugelers, W.J.T., Witkamp, G.J.
The influence of variable physical properties and buoyancy on heat exchanger design for near- and supercritical conditions
(2005) Journal of Supercritical Fluids, 34 (1), pp. 99-105.
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ABSTRACT: Computational fluid dynamics simulations were done on heated supercritical carbon dioxide flowing up or down in a vertical pipe. The impairment or enhancement of heat transfer caused by the temperature-induced variation of physical properties was investigated, as well as the effect of buoyancy. The simulations show, for non-buoyant flow, that for pressures above 120 bar, the effect of variation in physical properties is small and a constant-property Nusselt relation can be used for a heat exchanger design. For pressures below 120 bar, the variation in physical properties has to be taken into account for a correct heat exchanger design. For non-buoyancy conditions the Krasnoshchekov-Protopopov equation can be used to calculate heat transfer coefficients. It was observed that buoyancy can enhance heat transfer coefficients up to a factor 3. When buoyancy is active, the highest heat transfer coefficients are realized when the fluid flows downward. The Jackson and Hall correction factor for the calculation of heat transfer coefficients under buoyancy was confirmed by the simulations. © 2004 Elsevier B.V. All rights reserved.
Gärtner, R.S., Wilhelm, F.G., Witkamp, G.J., Wessling, M.
Regeneration of mixed solvent by electrodialysis: Selective removal of chloride and sulfate
(2005) Journal of Membrane Science, 250 (1-2), pp. 113-133.
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ABSTRACT: The applicability of electrodialysis for the selective removal of sulfate and chloride ions from a mixed solvent solution of sodium carbonate is investigated. The mixed solvent consists of 70 wt.% ethylene glycol and 30 wt.% water. Six different ion exchange membranes, the homogeneous membranes Neosepta CM-2, AM-3, AMX and ACM as well as the heterogeneous FuMA Tech CM-A and AM-A, are tested for their chemical and physical resistance to the mixed solvent carbonate solution, their ethylene glycol retention, their electrical resistance in the mixed solvent and their selectivity for sulfate and chloride over carbonate transport. © 2004 Elsevier B.V. All rights reserved.
Kersch, C., Witkamp, G.J., Woerlee, G.F.
Supercritical fluid extraction: A study on metal recovery and regeneration of β-diketones and organophosphorus extractants
(2005) Solvent Extraction and Ion Exchange, 23 (2), pp. 189-212.
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ABSTRACT: For the design of extraction processes that are feasible both environmentally and economically, suitable extractants are required that result in high extraction and that are recyclable. Therefore, the relation between metal-complex stability and extractant dissociation at standard conditions has been investigated. Complex stability versus dissociation of extractants with non-coordinating side chains resulted in a linear reference line. This line helps tinding extractants optimised for both extraction (of metals) and recovery (of extractants and metals). The solubilities of acetylacetonate complexes with Cu, Zn, Ni, and Co in supercritical CO2 were determined. Regeneration experiments under supercritical conditions have been carried out using a packed countercurrent column. Metal recovery of Cu, Zn, Ni, and Co from supercritical CO2 into nitric acid was shown by decomplexation from both a β-diketone (acetylacetone) and an organophosphorus compound (Cyanex 272). Copyright © Taylor & Francis, Inc.
Pillay, V., Gärtner, R.S., Himawan, C., Seckler, M.M., Lewis, A.E., Witkamp, G.-J.
MgSO4 + H2O system at eutectic conditions and thermodynamic solubility products of MgSO4·12H2O(s) and MgSO4·7H2O(s)
(2005) Journal of Chemical and Engineering Data, 50 (2), pp. 551-555.
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ABSTRACT: A thermodynamic electrolyte model has been used to investigate the system MgSO4 + H2O at temperatures dose to the eutectic from (0 to -10)°C. The model was based on the Pitzer aqueous electrolyte activity coefficient model using the interaction parameters proposed by Marion and Farren (Marion, G.; Farren, R. E. Mineral solubilities in the Na-K-Mg-Ca-Cl-SO 4-H2O system: A re-evaluation of the sulfate chemistry in the Spencer-Møller-Weare model. Geochim. Cosmochim. Acta 1999, 63, 1305-1318) as well as improved functions that have been derived in this work. Because of its improved data fitting, the model describes the system MgSO 4 + H2O accurately from (-5 to 50)°C. By making use of solubility data obtained from the literature as well as from additional laboratory experiments, we investigated the magnesium sulfate duodecahydrate solid phase (MgSO4·12H2O). The two characteristic points, which limit the MgSO4· 12H2O(s) region of existence, are the eutectic point between MgSO4·12H 2O(s) and ice and the phase-transition point (peritectic) between MgSO4-12H2O(s) and MgSO4·7H 2O(s) (epsomite, bitter salt). Both were determined from the solubility experiments and the model. The solubility products (Ksp) of MgSO4· 12H2O(s) and MgSO4· 7H2O(s) were calculated as functions of temperature from solubility and phase stability data. These functions improve Ksp functions published by Marion and Farren (Marion, G.; Farren, R. E. Mineral solubilities in the Na-K-Mg-Ca-Cl-SO4-H2O system: A re-evaluation of the sulfate chemistry in the Spencer-Møller-Weare model. Geochim. Cosmochim. Acta 1999, 63, 1305-1318). It was experimentally determined that the eutectic occurs at 17.4 mass % MgSO4 and -3.7°C, and the presented model predicts it at 17.3 mass % MgSO4 and -3.7°C. © 2005 American Chemical Society.
Genceli, F.E., Himawan, C., Witkamp, G.J.
Inline determination of supersaturation and metastable zone width of MgSO4.12H2O with conductivity and refractive index measurement techniques
(2005) Journal of Crystal Growth, 275 (1-2), pp. e1757-e1762.
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ABSTRACT: Inline measurement of the supersaturation is important to support process control and for the evaluation of crystallization experiments. Especially, when different hydrates or polymorphs of the crystallized component occur, very precise measurement is required. For example MgSO4.7H 2O-MgSO4.12H2O lines are quite close, and when operating under eutectic freeze crystallization (EFC) or cooling crystallization both salts might be produced. Therefore conductivity and refractive index inline measurement methods are investigated and compared for MgSO4 solution having concentration range between 16 and 22 wt% and temperature range between 10 and -5 °C. Conductivity measurements are correlated to concentrations and temperature with the empirical Casteel-Amis equation and refractivity index measurements are correlated to concentrations and temperature with a developed empirical model. The metastable lines for ice and salt of MgSO4 system is drawn based on the measurements at the onset of crystallization upon cooling of several solution concentrations. In the working range of EFC, the relative supersaturations are calculated to be σicemax=0.2 and σsaltmax=0.23. The accuracy for conductivity measurement in relation to the metastable zone width is roughly calculated to be around 20% and for refractive index measurements, 3%. © 2004 Elsevier B.V. All rights reserved.
Pronk, P., Infante Ferreira, C.A., Witkamp, G.J.
A dynamic model of Ostwald ripening in ice suspensions
(2005) Journal of Crystal Growth, 275 (1-2), pp. e1355-e1361.
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ABSTRACT: A computer-based dynamic model of Ostwald ripening in ice suspensions in a storage tank containing crystal growth kinetics, population, mass and energy balances has been developed to simulate the development of ice crystal size distributions during adiabatic ice slurry storage. The model assumed a homogeneously mixed storage tank with neither inlet nor outlet of mass. Growth and melting of ice crystals were caused by differences in equilibrium temperatures between differently sized crystals and crystal growth kinetics were based on heat and mass transfer. Validation with experimental results for different types and concentration of solutes, different ice fractions and different mixing rates showed that the model is able to predict the development of the average crystal size in time. Especially, the former two parameters have a strong effect on the ripening process, while the effect of the latter two is small. A difference between experimental and simulation results was found for the shape of the crystal size distribution curve after storage, which had a slightly longer tail during the experiments. © 2004 Elsevier B.V. All rights reserved.
Gärtner, R.S., Genceli, F.E., Trambitas, D.O., Witkamp, G.J.
Impurity gradients in solution-grown ice and MgSO4 · 12H 2O crystals measured by cryo-laser ablation and high-resolution- induced-coupled plasma mass spectrograph
(2005) Journal of Crystal Growth, 275 (1-2), pp. e1773-e1778.
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ABSTRACT: During the eutectic freeze crystallization (EFC) of an industrial aqueous MgSO4 solution, ice and magnesium sulfate duodecahydrate (MgSO4·12H2O(s)) were crystallized simultaneously near the eutectic point. It was found that the crystallization was highly selective: although the industrial feed solution contained appreciable levels of inorganic impurities (typically: 320mg/LCl-, 410mg/LCa2, 40mg/LMn2+, 70mg/LNa+ and 50mg/LK+), the formed ice and salt crystals contained lower levels of impurities (typically: 17mg/LCl-, 8mg/LCa2+, 17mg/LMn2+, and 5mg/LNa). Also the ice was pure: only traces (typically: 20mg/LSO42- and 5mg/LMg2+) of magnesium and sulfate were found in the ice crystals. In this work the spatial distribution of the impurities in the crystals is investigated. Gradients of composition in solids are measured by laser ablation high-resolution inductively coupled plasma mass spectrometry (LA-HR-ICP-MS). A special cryogenic sampling cell (<-80°C) for laser ablation has been constructed. The focused (5-10μm width) laser shoots at the frozen sample, scanning its surface. The vapor is fed to the mass spectrometer. In this way, the impurity concentration as a function of position in the crystal can be measured. The results of this method with MgSO4·12H2O and ice are presented. © 2004 Elsevier B.V. All rights reserved.
Genceli, F.E., Gärtner, R., Witkamp, G.J.
Eutectic freeze crystallization in a 2nd generation cooled disk column crystallizer for MgSO4·H2O system
(2005) Journal of Crystal Growth, 275 (1-2), pp. e1369-e1372.
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ABSTRACT: Eutectic freeze crystallization is a new separation process to produce pure ice and salt from concentrated salt solutions. For this new process, specialized crystallizers are being developed. A new, 2nd generation cooled disc column crystallizer (CDCC-2) with 150-l capacity and 5.6 m2/m 3 cooling area was designed and tested for MgSO4 crystallization. A heat flux of 1720-5750 W/m2 was achieved at a temperature difference between coolant and crystallizer bulk solution of 3-6.5 K and a residence time of 1-3 h. Crystallization and gravitational separation of ice and salt are discussed. © 2004 Elsevier B.V. All rights reserved.
Pronk, P., Hansen, T.M., Ferreira, C.A.I., Witkamp, G.J.
Time-dependent behavior of different ice slurries during storage
(2005) International Journal of Refrigeration, 28 (1), pp. 27-36.
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ABSTRACT: One of the main advantages of ice slurry as secondary refrigerant is the possibility of cold storage, which enables load shifting and peak shaving. During cold storage, ice crystals are subject to mechanisms as attrition, agglomeration and Ostwald ripening causing changes in the crystal size distribution, which are of great importance for ice slurry systems since they influence other parameters such as pressure drop and heat transfer characteristics. Storage experiments with ice crystals in aqueous solutions of sodium chloride, ethylene glycol, ethanol and propylene glycol show that Ostwald ripening is the most important mechanism inducing an increase in average crystal size. The ripening rate strongly decreases as the solute concentration increases and the type of solute and the mixing regime also play an important role. The different ripening rates are caused by the fact that crystal growth and dissolution by means of Ostwald ripening are mainly limited by surface integration kinetics at low concentrations and by mass transfer at high solute concentrations. © 2004 Elsevier Ltd and IIR. All rights reserved.
Kroon, M.C., Shariati, A., Costantini, M., Van Spronsen, J., Witkamp, G.-J., Sheldon, R.A., Peters, C.J.
High-pressure phase behavior of systems with ionic liquids: Part V. the binary system carbon dioxide + 1-butyl-3-methylimidazolium tetrafluoroborate
(2005) Journal of Chemical and Engineering Data, 50 (1), pp. 173-176.
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ABSTRACT: The phase behavior of the binary system consisting of the supercritical fluid carbon dioxide (CO2) and the ionic liquid l-butyl-3-methylinudazolium tetrafluoroborate ([bmim][BF4]) was studied experimentally. A synthetic method was used to measure its phase behavior. Bubble-point pressures of the system CO2 + [bmim][BF 4] are reported for carbon dioxide concentrations ranging from (10. 22 to 60.17) mole % and within a temperature fange of (278.47 to 368.22) K. The CO2 + [bmim][BF4] binary system has a twophase liquid-vapor region extending up to very high pressures. Most likely, the type of fluid-phase behavior is type III according to the classification of Scott and Van Konynenburg. The experimental results obtained were compared with the available phase behavior data of the binary system CO2 + l-hexyl-3methylimidazolium tetrafluoroborate ([hmim][BF4]) to investigate the effect of the length of the alkyl group on the phase behavior of this type of system. A larger alkyl group leads to lower bubble-point pressures and, therefore, to higher solubilities of carbon dioxide in the imidazolium-based ionic liquid.
Van Roosmalen, M.J.E., Woerlee, G.F., Witkamp, G.J.
Amino acid based surfactants for dry-cleaning with high-pressure carbon dioxide
(2004) Journal of Supercritical Fluids, 32 (1-3), pp. 243-254.
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ABSTRACT: The currently most used dry-cleaning solvent is perchloroethylene (PER). Carbon dioxide could be an ideal solvent to replace PER. Amino acid based surfactants have been studied for dry-cleaning with carbon dioxide. For the production of amino acid based surfactants, renewable, low-cost raw materials are used. Furthermore, these surfactants have a low toxicity, are biodegradable and not skin irritating. These characteristics make the amino acid based surfactants attractive for dry-cleaning with carbon dioxide. The amino acid based surfactants give good results for dry-cleaning with liquid CO2. The surfactant Amihope LL (N-lauroyl-L-lysine) gives the best cleaning-results. An important process parameter using this surfactant is the addition of water. The addition of water is required for sufficient removal of non-particulate soils. However, when no water is added to the system, there is a large increase in particulate soil removal. Therefore, a two-bath process is proposed. The first bath is for particulate soil removal and has optimal conditions for particulate soil removal; the second bath has optimal conditions for non-particulate soil removal. The two-bath process using Amihope LL gives excellent results: the result for particulate soil removal is 84% compared to the results for PER, the result for non-particulate soil removal is 98% compared to PER and the overall result is 92% compared to PER. © 2004 Elsevier B.V. All rights reserved.
Fernandez Cid, M.V., Van Der Kraan, M., Veugelers, W.J.T., Woerlee, G.F., Witkamp, G.J.
Kinetics study of a dichlorotriazine reactive dye in supercritical carbon dioxide
(2004) Journal of Supercritical Fluids, 32 (1-3), pp. 147-152.
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ABSTRACT: The kinetics of the reaction between a dichlorotriazine reactive dye and methanol was studied in supercritical carbon dioxide and in a solution of pure methanol. The experiments were carried out in a batch reactor at different temperatures between 333 and 393 K and at 300 bar when supercritical carbon dioxide was the solvent medium. The rate constants and the parameters of the Arrhenius equation were determined and compared. A significant influence of the supercritical carbon dioxide on the rate constants was found. The formation of methoxy-dye was faster over the whole temperature range in pure methanol than in supercritical carbon dioxide. But the consecutive reaction, the formation of dimethoxy-dye, was considerably faster, up to 20 times, in supercritical carbon dioxide than in pure methanol. Moreover, the lowest value for the activation energy, 50 ± 13 kJ mol-1, was found for the consecutive reaction in supercritical carbon dioxide. In this paper new kinetic data for the methanolysis reaction of a dichlorotriazine reactive dye in supercritical carbon dioxide are shown. © 2004 Elsevier B.V. All rights reserved.
Jovanović, N., Bouchard, A., Hofland, G.W., Witkamp, G.-J., Crommelin, D.J.A., Jiskoot, W.
Stabilization of proteins in dry powder formulations using supercritical fluid technology
(2004) Pharmaceutical Research, 21 (11), pp. 1955-1969.
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ABSTRACT: Therapeutic proteins have become essential in the treatment of many diseases. Their formulation in dry form is often required to improve their stability. Traditional freeze-drying or spray-drying processes are often harmful to labile proteins and could be replaced by supercritical fluid (SCF) drying to produce particles with defined physicochemical characteristics in a mild single step. A survey of the current SCF drying processes for proteins is presented to give insight into the effect of SCF drying on protein stability and to identify issues that need further investigation. Methods used for drying aqueous and organic protein solutions are described. In particular, effects of process and formulation parameters on particle formation and protein stability are discussed. Although SCF methodology for drying proteins is still in its infancy, it can provide a serious alternative to existing drying methods for stabilizing proteins. © 2004 Springer Science+Business Media, Inc.
Pérez, Y., Wubbolts, F.E., Witkamp, G.J., Jansens, P.J., De Loos, Th.W.
Improved PCA process for the production of nano- and microparticles of polymers
(2004) AIChE Journal, 50 (10), pp. 2408-2417.
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ABSTRACT: The system dextran-DMSO-CO2 has been chosen as a model system to study the fundamentals of the precipitation of biodegradable polymers, using the precipitation with a compressed antisolvent (PCA) process. At conditions of completely miscibility between the organic solvent (DMSO) and CO2, it is proposed that the formation of droplets in the system is not the consequence of atomization of the DMSO solution, but rather the result of the occurrence of a liquid-liquid phase split when the DMSO-solution and CO2 are intimately mixed. Penetration of CO2 into the droplets and stripping of DMSO induces the solidification of these droplets. A new device was designed to separate the three steps involved in the process: mixing of CO2 and solution, liquid- liquid phase split, and stripping of the solvent. This new device eliminates agglomeration of particles, and yields reproducible results. The particle size can be easily manipulated over a size range from several nanometers to tenths of microns by changes in the operating conditions. The influence of these operating conditions (pressure, temperature, polymer concentration, and solution/CO2 composition ratio) on particle morphology has been studied. © 2004 American Institute of Chemical Engineers.
Van Roosmalen, M.J.E., Woerlee, G.F., Witkamp, G.J.
Surfactants for particulate soil removal in dry-cleaning with high-pressure carbon dioxide
(2004) Journal of Supercritical Fluids, 30 (1), pp. 97-109.
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ABSTRACT: The removal of particulate soils from textile in dry-cleaning with CO 2 is insufficient compared to perchloroethylene (PER). Especially the removal of relatively small particles (<20 μm) poses a problem. Various anionic and amine based surfactants have been investigated to enhance the removal of particulate, but also of non-particulate soils in dry-cleaning with high-pressure CO2. The cleaning performance index for relatively small particulate soil (CPIpart) increased from 24% (when no surfactants were used) to a maximum of 51% (when surfactants were used), which shows that particle removal is possible in CO2 dry-cleaning. The use of these surfactants, however, does not bring particle removal up to the level of PER (CPIpart of 68%). The removal of non-particulate soils in CO2 with water, surfactant and co-solvent is better than in PER. The overall results using the investigated surfactants are promising; the overall result increases from 70% (when no surfactants are used) to 87% (when surfactants are used) compared to the level when using PER. Surfactant particles were formed in all experiments. In the case of the amines, these particles may be formed by reaction. The formed charged surfactant particles are probably responsible for the removal of the soil particles from the textile. The charged surfactant particles may adhere to the soil particles and/or fabric, thereby establishing an element of repulsion and/or a steric barrier. The use of a co-solvent (iso-propanol) had a positive effect on the removal of particulate and non-particulate soils when using amines. However, when anionic surfactants were used, the addition of a co-solvent had a pronounced negative effect on particulate soil removal. © 2003 Elsevier B.V. All rights reserved.
Vaessen, R.J.C., Seckler, M.M., Witkamp, G.J.
Heat transfer in scraped eutectic crystallizers
(2004) International Journal of Heat and Mass Transfer, 47 (4), pp. 717-728.
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ABSTRACT: Heat transfer phenomena in two types of eutectic crystallizers have been analyzed. This equipment is equipped with rotating scraper blades and the effect of the blade action on heat transfer phenomena in both crystallizing and non-crystallizing conditions is studied. It was found that the coolant flow in the equipment can be described by fitted Dittus-Boelter relations. In both crystallizers the transport of heat from process liquid to cooled wall surfaces at various rotational speeds of the scrapers can generally be accurately described with penetration theory. Exceptions are approximated with fitted Re-Pr-relations. Both increasing and decreasing heat transfer rates have been found in crystallizing conditions at increasing scraping rates. Differences are attributed to geometrical crystallizer characteristics and solid content. © 2003 Elsevier Ltd. All rights reserved.
van der Ham, F., Seckler, M.M., Witkamp, G.J.
Eutectic freeze crystallization in a new apparatus: The cooled disk column crystallizer
(2004) Chemical Engineering and Processing: Process Intensification, 43 (2), pp. 161-167.
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ABSTRACT: Eutectic freeze crystallization (EFC) is a technique for simultaneous crystallization of ice and salt that is energetically more efficient than conventional evaporative crystallization. In this paper, a new type of crystallizer is introduced for simultaneously conducting EFC and separating the ice from the salt crystals, the cooled disk column crystallizer (CDCC). Crystallization is achieved by indirect cooling with wiped disks and separation by means of gravity. The liquid feed stream enters the column at the center, ice leaves the column at the top and salt is discharged at the bottom. The heat flux from bulk fluid to disk in a 14 l CDCC using CuSO4-water as a model system (eutectic temperature -1.6 °C) was 1.9 kW m-2 for a temperature difference between disk and bulk of 4.5 K. The CuSO4 · 5H2O crystals formed were well faceted with an average size of 200 μm. Ice crystals were disk shaped with an average size 150 μm. Both ice and salt crystals were easily filtered. The impurity level in the ice crystals was below 100 ppm Cu. © 2003 Elsevier B.V. All rights reserved.
Kersch, C., Peretó Ortiz, S., Woerlee, G.F., Witkamp, G.J.
Leachability of metals from fly ash: Leaching tests before and after extraction with supercritical CO2 and extractants
(2004) Hydrometallurgy, 72 (1-2), pp. 119-127.
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ABSTRACT: Residues such as sewage sludge or fly ashes are usually contaminated with toxic heavy metals. These metals leach out after contact with water, thus polluting the groundwater. If aqueous concentrations of metals are exceeded, these residues require expensive disposal. Supercritical fluid extraction (SFE) is a promising method to reduce the metal content of contaminated particles to such an extent that leachability is reduced and the demands of legislation are observed. This paper focuses on the metal leachability and the effect after extraction in a 12-L revolving vessel with supercritical CO2 with fly ash from a municipal waste incinerator as model compound. Pre-leaching with water prior to SFE led to the removal of water-soluble compounds and structural changes on the ash surface. Standard leaching tests of fly ash after SFE with Cyanex 302, TBP, D2EHPA, or mixtures of TBP-D2EHPA focussed on metals such as Zn, Pb, Mn, Cd, Cu, V, Sb, Ni, Mo, Cr, and Co. The leaching test showed a leachability increase of Sb and the successful reduction in leachability of Zn, Pb, and Mn in particular. © 2003 Elsevier B.V. All rights reserved.
Kersch, C., Woerlee, G.F., Witkamp, G.J.
Supercritical Fluid Extraction of Heavy Metals from Fly Ash
(2004) Industrial and Engineering Chemistry Research, 43 (1), pp. 190-196.
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ABSTRACT: Currently expensive measures for disposal of fly ash residues from coal-fired power plants (CFP) or from municipal solid waste incinerators (MSWI) are required to prevent the pollution of groundwater with water leachable metals. For the reuse in road pavement as a substitute for sand- or cement-stabilized subbases, only a minimal leachability of metals is allowed by national legislation. Supercritical fluid extraction (SFE) is a promising method to lower the leachable metal content of fly ash to such an extent that the legal demands are obeyed. This paper presents results of SFE with SC-CO 2 from fly ash of both CFP and MSWI for Zn, Pb, Mn, Cd, Cu, V, Sb, Ni, Mo, Cr, and Co. Extraction from 2 kg of fly ash was carried out with a 12 L rotating extraction vessel, a constant solvent flow, and various complexing extractants. Depending on the metal, extraction efficiencies from 0 to 98% were obtained. The positive influence of time and initial moisture content was demonstrated for SFE with Cyanex 302. SFE with equimolar mixtures of TBP-D 2EHPA resulted in synergistic effects for Pb and Cu, while extraction of Zn was insignificantly low with TBP, D2EHPA, or a mixture of TBP-D2EHPA.
Gärtner, R.S., Seckler, M.M., Witkamp, G.-J.
Solid phases and their solubilities in the system Na2CO3 + NaHCO3 + ethylene glycol + water from (50 to 90) °C
(2004) Journal of Chemical and Engineering Data, 49 (1), pp. 116-125.
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ABSTRACT: Solubilities in the system sodium carbonate + sodium bicarbonate were measured over a range of temperatures from (50 to 90) °C in mixed aqueous solvents containing (50 to 100) mass % (salt-free solvent) ethylene glycol. Mixtures of solid sodium carbonate anhydrate (Na2CO3(s)) and solid sodium bicarbonate (NaHCO3(s)) in different ratios and also trona (Na2CO3·NaHCO3·2H2O(s) ) were allowed to recrystallize and equilibrate with the mixed solvents at the given temperatures. The solubility of CO3 2- was generally found to decrease with increasing ethylene glycol content irrespective of the occurring solid phase, while HCO3 - solubility displayed a minimum at (80 to 90) mass % (salt-free solvent) ethylene glycol and then increased sharply. For pure carbonate phases, CO3 2- solubility displayed little temperature dependence. In equilibrium with mixed carbonate-bicarbonate phases, the CO3 2- solubility usually decreased with temperature, most likely because it was linked to the HCO3 - concentration via the solid's solubility product. The solubility of HCO3 - increased significantly with temperature for all sodium bicarbonate containing solid phases. For the temperature range from (30 to 90)°C and an ethylene and glycol concentration range of (50 to 100) mass % (of salt-free solvent), the CO3 2- solubility varied between (0.058 and 1.023) mol/kg solution, and the HCO3 - solubility concentration ranged between 0.000 (i.e. the lower detection limit of the analytical method) and 1.153 mol/kg solution. The occurring solid phases were the same as those formed in the aqueous system. The were identified in the recrystallization experiments as sodium carbonate anhydrate (Na2CO3(s)), sodium carbonate monohydrate (Na2CO3·H2O(s)), trona (Na2CO3 ·NaHCO3·2H2O(s)), wegscheiderite (Na2CO3·3NaHCO3(s)), and sodium bicarbonate (NaHCO3(s)). No solvate phases with ethylene glycol were observed.
Bremere, I., Kennedy, M., Johnson, A., Witkamp, G.-J., Schippers, J.
Optimising dose of antiscalant in membrane filtration systems using a desupersaturation unit
(2003) Water Science and Technology: Water Supply, 3 (5-6), pp. 147-153.
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ABSTRACT: The strategy behind the desupersaturation unit (DU) is rapid desupersaturation of the membrane concentrate stream by forced precipitation of sparingly soluble inorganic compounds on seed crystals. The efficiency of deposition will depend on the supersaturation and the condition of seeds, i.e. their reactivity. Poisoning of seeds by adsorption of natural organic matter and/or added commercial antiscalant will hinder the desupersaturation efficiency by blocking centres available for crystallisation. Barium sulphate precipitation in a laboratory scale DU was examined from natural reverse osmosis (RO) concentrates from surface water treatment pilot plant. Tests indicated similar effects on poisoning the barite seed grains by commercial antiscalant and natural organic matter from surface water (the Rhine River) treatment RO pilot plant (80% conversion) while no effect was observed from supersaturated synthetic (no organic matter) concentrate. An attempt was made to relate the effects of organic matter and the RO system conversion (50-85%). The rate of barite seed grain poisoning was attributed to the relative barium supersaturation in the concentrate. The efficiency of natural organic compounds started to decline above the supersaturation ratio of 3.3. Addition of commercial antiscalant enhanced the effect of natural organic matter. If the effects of organic matter in membrane systems are quantified and related to the RO system conversion, a laboratory DU can practically be used to control scaling.
Van Roosmalen, M.J.E., Woerlee, G.F., Witkamp, G.J.
Dry-cleaning with high-pressure carbon dioxide - The influence of process conditions and various co-solvents (alcohols) on cleaning-results
(2003) Journal of Supercritical Fluids, 27 (3), pp. 337-344.
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ABSTRACT: The influence of the process conditions time and temperature on dry-cleaning results with CO2 has been examined in a 25 1 vessel. The optimal cleaning-time lay between 5 and 20 min. There was not one optimal cleaning temperature; therefore, it is considered to perform the process at room temperature (no use of heating or cooling during the process). For most soils, the use of a co-solvent caused a substantial increase in their removal. Of the co-solvents investigated, 2-propanol was the most suitable. © 2003 Elsevier Science B.V. All rights reserved.
Vaessen, R.J.C., Janse, B.J.H., Seckler, M.M., Witkamp, G.J.
Evaluation of the performance of a newly developed eutectic freeze crystallizer: Scraped cooled wall crystallizer
(2003) Chemical Engineering Research and Design, 81 (10), pp. 1363-1372.
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ABSTRACT: Eutectic freeze crystallization (EFC) separates aqueous inorganic solutions into pure water and pure salt. By operating at the eutectic point, ice and salt can be formed simultaneously as two separate phases. The scraped cooled wall crystallizer (SCWC), specially developed for eutectic operation, is introduced. It features cooling through an outer wall combined with an internal cooling cylinder. Experiments were executed in a 1151 model SCWC using a ternary aqueous system of KNO3-HNO3. The SCWC is equipped with temperature sensors measuring bulk temperature and the temperatures of the coolant entering and exiting the cooling walls. The total heat flux from coolant to bulk equals 490-585 W m-2 K-1 at a temperature difference between cooling wall and bulk of 5-6K. At this heat flux the production capacity equals 3.8 × 10-4 kg m-2 K-1 s-1 for ice and 3.1 × 10-5 kg m-2 K-1 s-1 for salt. The KNO3 crystals produced are reasonably well faceted with average size of 80-230 μm. Both ice and salt crystals are easily filtered. Impurities in the ice crystals drop below 50 ppm K+-ions after three washings. Ice solid content measurements indicated that 0.01 wt% of the ice slurry consisted of entrained salt crystals. Washed salt samples contained less than 5 ppm of ionic impurities while impurity levels in the feed ranged from 50 to 500 ppm.
Vaessen, R., Seckler, M., Witkamp, G.J.
Eutectic freeze crystallization with an aqueous KNO3-HNO 3 solution in a 100-L cooled-disk column crystallizer
(2003) Industrial and Engineering Chemistry Research, 42 (20), pp. 4874-4880.
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ABSTRACT: Eutectic freeze crystallization is a novel technique for processing waste and process streams of aqueous electrolyte solutions, separating them into pure water and pure solid salt. A dedicated apparatus, a 100-L cooled-disk column crystallizer, has been developed and tested, combining crystallization and solid/solid separation of ice and salt. Experiments have been performed with a ternary system of aqueous KNO3-HNO3. Heat-transfer rates were achieved in the range of 1300-4600 W·m-2·K -1, which are related to the square root of the scraping rate. The ice product slurry contained 0.15 wt % salt. The ice impurity content after three washing cycles was as low as 15 ppm K+. Well-faceted KNO 3 crystals are produced with high purity.
Hofland, G.W., Berkhoff, M., Witkamp, G.J., Van Der Wielen, L.A.M.
Dynamics of precipitation of casein with carbon dioxide
(2003) International Dairy Journal, 13 (8), pp. 685-697.
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ABSTRACT: Carbon dioxide is a green alternative for mineral acids (e.g., sulphuric acid) in protein precipitation. The precipitation using a gaseous precipitant differs from the conventional precipitation in the way and the rate at which the precipitant can be applied to the aqueous solution. In this paper, the consequences of using carbon dioxide were investigated for the precipitation of the milk protein casein. Product properties, such as particle size, solids content and calcium release were investigated in a batch system at various mixing conditions and gas addition rates. In addition, mass transfer coefficients were determined from pH response data. The experiments revealed a strong influence of stirring rate and gas flow rate on the particle size. The main effect of varying the gas flow was through the change of acidification rate, much alike precipitation with sulphuric acid. At high acidification rates, the particle size of casein precipitated with carbon dioxide was smaller than with sulphuric acid. © 2003 Elsevier Ltd. All rights reserved.
Van Roosmalen, M.J.E., Van Diggelen, M., Woerlee, G.F., Witkamp, G.J.
Dry-cleaning with high-pressure carbon dioxide - The influence of mechanical action on washing-results
(2003) Journal of Supercritical Fluids, 27 (1), pp. 97-108.
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ABSTRACT: Previous studies indicate that the removal of non-polar soils in CO 2 is comparable to the level of dry-cleaning in perchloroethylene (PER). However, these studies show that the removal of particulate soil is insufficient in CO2 compared to PER. Particle removal can be increased by the use of more mechanical action and/or the use of surfactants. From experiments, it is concluded that the removal of relatively large particles like sand increases with increasing mechanical action. However, the level of mechanical action has no influence on the removal of relatively small particulate and non-particulate soils (with the exception of clay on wool). Increasing the amount of mechanical action is therefore not the solution that will lead to the increase of the washing-results for relatively small particles (like carbon black and clay) up to the level of the washing-results using PER. The removal of relatively small particulate soils in CO2 can be improved by the use of suitable surfactants that reduce adhesion forces. A model for quantifying the amount of mechanical action has been developed. This model can be used to predict the optimal process conditions for relatively large particle removal. It is concluded (from the model and experiments) that the level of highest mechanical action in CO2 is obtained in a two-phase environment at low pressure and temperature and that 75 RPM is the optimal number of revolutions in our system. At these conditions, however, the washing-results for small particles are not as good as the washing-results for these particles in PER. © 2002 Elsevier Science B.V. All rights reserved.
Hofland, G.W., Berkhoff, M.R., Witkamp, G.J., Van der Wielen, L.A.M.
Dynamics of isoelectric precipitation of casein using sulfuric acid
(2003) AIChE Journal, 49 (8), pp. 2211-2223.
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ABSTRACT: The acid precipitation of casein from skim milk is an interesting and complex operation, as it involves several mechanistic steps occurring simultaneously. Research has focused so far on the influence of static variables such as temperature and final pH on the curd properties. Here the dynamics of the process was investigated. From a characteristic times analysis it was concluded that the most important mechanistic steps in the acid precipitation of casein were acid mixing, aggregation/breakup, and transport in/out of the precipitate particles. Experiments in a fed batch setup using sulfuric acid as the precipitant showed how the precipitation influenced the pH profile and demonstrated the large influence of process variables, such as the acid addition rate, the mixing intensity, and aging time on particle-size distributions and the release of minerals from the casein.
Ma, M., Zhu, W., Wang, Z., Witkamp, G.J.
Accumulation, assimilation and growth inhibition of copper on freshwater alga (Scenedesmus subspicatus 86.81 SAG) in the presence of EDTA and fulvic acid
(2003) Aquatic Toxicology, 63 (3), pp. 221-228.
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ABSTRACT: Accumulation and growth inhibition of Cu to fresh water alga (Scenedesmus subspicatus 86.81 SAG) and the influences of ethylenediaminetetraacetic acid (EDTA) and fulvic acid (FA) were examined. These results demonstrated that both EDTA and FA could reduce toxicity of Cu to alga by the way of preventing Cu from being adsorbed by cell wall of alga. When dissolved Cu (Cudissolved), extracellular Cu (Cuextracellular), and intracellular Cu (Cuintracellular) were differentiated, our results showed that the concentration level of extracellular Cu ([Cuextracellular]) was a good indicator for measuring the toxic effects of Cu on alga growth in complex matrix. Either in the absence or in the presence of EDTA and FA, the concentration of intracellular Cu increased to 0.6-1.5×10-8 μM per cell when the growth inhibition reached to about 50%. We found that the acute toxicity of copper on unicellular alga could be interpreted by its accumulation at a discrete site or biotic ligand at alga cell wall and critical accumulation of Cu associated with EC50 was determined to be 1×10-8 μM per cell. Therefore, the Biotic Ligand Model (BML) could be extended to predict the influence of copper on growth inhibition of alga. © 2002 Elsevier Science B.V. All rights reserved.
Xu, X., Zhu, W., Wang, Z., Witkamp, G.-J.
Accumulation of rare earth elements in maize plants (Zea mays L.) after application of mixtures of rare earth elements and lanthanum
(2003) Plant and Soil, 252 (2), pp. 267-277.
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ABSTRACT: Rare earth elements are applied in China to improve crop production, and the distribution patterns of individual rare earth elements in native plants have widely been reported. But our knowledge is still limited about the dose-dependent accumulation of individual rare earth elements in agricultural crops after application of rare earth elements. Effects of lanthanum and mixtures of rare earth elements were studied in pot experiments on the accumulation of individual rare earth elements in maize plants. All plant samples were divided into plant tops and roots. On addition of mixtures of rare earth elements and lanthanum to the soil, a significant dose-dependent accumulation of individual rare earth element(s) was found in the roots and in the plant tops. Application of mixtures of rare earth elements at >10 mg kg-1 soil, resulted in a significant increase in contents of light rare earth elements in the roots, and at a dose of 50 mg kg-1 soil, a similar phenomenon was found in the plant tops. When mixtures of rare earth elements were replaced by lanthanum alone, at a dose higher than 10 mg La kg-1 soil, a significant increase in La content occurred in the roots and in the plant tops. The content ratio of La to Ce in maize plants appeared to increase as the application doses of rare earth element(s) increased. At a highest dose (50 mg kg-1 soil), the transport of the absorbed La from the roots to the plant tops might be substantially reduced after treatment with lanthanum alone, compared with mixtures of rare earth elements. Increasing the application doses of rare earth element(s) appeared to cause a positive Gd and negative Ce anomaly in the roots and in the plant tops, and the anomaly was more obvious in the plant tops than in the roots. The results indicated that the Gd and Ce anomaly in corns might be considered as important parameters for the safety assessment of agricultural application of rare earth elements.
Xu, X., Zhu, W., Wang, Z., Witkamp, G.-J.
Distributions of rare earths and heavy metals in field-grown maize after application of rare earth-containing fertilizer
(2002) Science of the Total Environment, 293 (1-3), pp. 97-105.
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ABSTRACT: Rare earths are widely applied in Chinese agriculture to improve crop nutrition through the use of fertilizers, yet little is known of their accumulation in field-grown crops. We have studied the distribution of 16 rare earths (Sc, Y and 14 lanthanide elements) in field-grown maize and the concentration of heavy metals in the grains after application of rare earth-containing fertilizer. When maize entered the vigorous vegetation growth stage (e.g. early stem-elongation stage), rare earth-containing fertilizer was applied to the soil with irrigation water. At 10 days after application of the rare earths, significantly dose-dependent accumulative effects of individual rare earth concentrations in the roots and the plant tops of maize were observed, with the exception of Sc and Lu. At the level of 2 kg rare earths ha-1, accumulative concentrations of most light rare earths (e.g. La, Ce, Pr and Nd) and Gd in the plant tops were much larger than those in the control. Concentrations of individual rare earths in a field-grown maize after application of rare earths decreased in the order of root≫leaf>stem>grain. During the maize growth period, selective accumulation of individual rare earths (e.g. La, Ce) in the roots seemed to be in dynamic equilibrium, and the distribution of these elements in the plant tops was variable. At a dosage of less than 10 kg rare earths ha-1, no apparent accumulative concentrations of individual rare earths appeared in the maize grains. Under the experimental conditions, application of rare earth-containing fertilizer did not induce an increase in the concentrations of heavy metals in the grains. We conclude that the present dosage of rare earths (<0.23 kg ha-1 year-1) currently applied in China can hardly affect the safety of maize grains in arable soil, even over a long period. Copyright © 2002 Elsevier Science B.V.
Himawan, C., Vaessen, R.J.C., Kramer, H.J.M., Seckler, M.M., Witkamp, G.J.
Dynamic modeling and simulation of eutectic freeze crystallization
(2002) Journal of Crystal Growth, 237-239 (1-4 III), pp. 2257-2263.
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ABSTRACT: A computer-based dynamic model of an eutectic freeze crystallizer comprised of coupled kinetics, population, mass, and energy balances has been developed to simulate its transient behaviour. The model assumed an MSMPR crystallizer and was used to simulate the transient responses of crystal size distribution of salt and ice during the start-up of the crystallizer. The temperature and the solute concentration inside the crystallizer achieved constant values after two residence times, whereas the steady state of the crystal size distributions were reached after ten residence times. A coupled effect of the simultaneous crystallization of salt and ice was clearly visible when the high mass production rate of ice induced the occurrence of a second peak of the supersaturation of salt. © 2002 Elsevier Science B.V. All rights reserved.
Vaessen, R.J.C., Himawan, C., Witkamp, G.J.
Scale formation of ice from electrolyte solutions on a scraped surface heat exchanger plate
(2002) Journal of Crystal Growth, 237-239 (1-4 III), pp. 2172-2177.
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ABSTRACT: Freeze crystallization processes often suffer from an ice scale layer which is formed on cooling surfaces if no preventive action is taken. This causes a severe decrease in heat transfer rate, leading to stagnation of the crystallization process. Scraping of the heat transfer surface can prevent scaling of ice. This research investigates the phenomenon of ice scale formation on scraped cooled surfaces. Specific attention is paid to the influence of supersaturation, scraping rates and different electrolyte solutions of various concentrations. Ice formation experiments are performed with KNO3, HNO3 and CaCl2 solutions. An induction time is measured, determined by the minimum scraping rate required to keep the heat transfer surface free of an ice layer. The required scraping rate increased with increasing supersaturation. Comparison of HNO3 and CaCl2 experiments shows that besides thermodynamics other parameters play an important role in ice scale formation. Experiments with silicon scraper blades show that ice scaling is rather prevented by mechanical removal of the initial crystals than by refreshment of the thermal boundary layer. © 2002 Elsevier Science B.V. All rights reserved.
Gärtner, R.S., Witkamp, G.J.
Wet calcining of trona (sodium sesquicarbonate) and bicarbonate in a mixed solvent
(2002) Journal of Crystal Growth, 237-239 (1-4 III), pp. 2199-2204.
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ABSTRACT: Trona ore is used in large amounts for the production of soda ash. A key step in this process is the conversion of trona (sodium sesquicarbonate: Na2CO3·NaHCO3·2H2O) into soda (sodium carbonate anhydrate: Na2CO3). Currently, this conversion is done industrially by calcining of the raw ore in rotary calciners at ca. 120°C or higher (Natural Soda Ash - Occurrences, Processing, and Use, Van Nostrand Reinhold, New York, 1991, p. 267). Trona can however be converted at lower temperatures by using a "wet calcining" technique. In this technique, trona is contacted with an organic or mixed organic-aqueous solvent at a conversion temperature that depends on the water activity of the used solvent. In pure ethylene glycol this temperature can be as low as 55°C. The conversion by "wet calcining" occurs very similar to that in the regular dry calcining process via a solid phase conversion. The anhydrate crystals form directly from the solid trona. This produces pseudomorphs (J. Chem. Eng. Data 8(3) (1963) 301), i.e. agglomerates of fine anhydrate crystals (1-10 μm). At high temperatures, dense, finely pored agglomerates are formed, while the outer shape of the agglomerate retains the prism shape of the trona crystal. At low conversion temperatures, loosely packed or even unstable agglomerates are found. © 2002 Elsevier Science B.V. All rights reserved.
Kersch, C., Van Der Kraan, M., Woerlee, G.F., Witkamp, G.J.
Municipal waste incinerator fly ash: Supercritical fluid extraction of metals
(2002) Journal of Chemical Technology and Biotechnology, 77 (3), pp. 256-259.
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ABSTRACT: The amount of residues such as fly ash from municipal waste incinerators and coal-fired power plants is growing. Fly ash is usually contaminated with toxic heavy metals that leach out on contact with water and pollute the groundwater. Therefore, isolated and expensive disposal of the ash is required. Reuse of ash as a filler for cement or pavements only allows minimum leachability of metals and maximum leaching values of various metals from reused fly ash are prescribed by national legislation. Supercritical-fluid extraction (SFE) offers a method to reduce the metal content so that leachability is reduced and the demands of legislation are observed. This paper presents results of metal extraction from municipal waste incinerator ash using supercritical CO2. Initial experiments with a 12dm3 rotating extraction vessel and constant solvent flow showed extraction efficiencies of between 10% and 52%. The influences of complexing-agent concentration and process time are studied on divalent metals such as Zn2+, Pb2+, Cu2+, Sb2+, Ni2+, and Cd2+. © 2002 Society of Chemical Industry.
Boerlage, S.F.E., Kennedy, M.D., Bremere, I., Witkamp, G.J., Van Der Hoek, J.P., Schippers, J.C.
The scaling potential of barium sulphate in reverse osmosis systems
(2002) Journal of Membrane Science, 197 (1-2), pp. 251-268.
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ABSTRACT: Barium sulphate scaling in reverse osmosis (RO) causes flux decline and potentially severe membrane damage. Existing methods, e.g. Du Pont, predict barite scaling when the concentrate is saturated. However, precipitation in supersaturated concentrate may be limited by slow nucleation kinetics, measured as long induction times. Induction time decreases, hence precipitation is more likely, with supersaturation and temperature. Therefore, induction time may be used to express the scaling potential of RO concentrate. This research aims to develop a more realistic method to predict barite scaling based on the assumption that an induction time (unsafe) can be defined, operating below which scaling will most likely occur in an RO system. While operating above a certain induction time (safe) should prevent scaling. Induction times were calculated for various supersaturation (employing Pitzer coefficients) and temperature conditions at an RO pilot plant using a previously derived relationship of measured induction time versus supersaturation at 25°C. Safe (≥10h) and unsafe (≤5h) induction time limits, were derived from periods when scaling did and did not occur in the RO system and translated into safe and unsafe supersaturation limits for 5-25°C. Use of these supersaturation limits allows more flexible operation in optimising RO recovery while avoiding scaling. The general validity of these limits needs to be verified in further pilot studies with feedwater of different quality and using different RO elements. Copyright © 2002 Elsevier Science B.V.
Oosterhof, H., De Graauw, J., Witkamp, G.-J., Van Rosmalen, G.M.
Continuous Double Recrystallization of Light Soda Ash into Super Dense Soda Ash
(2002) Crystal Growth and Design, 2 (2), pp. 151-157.
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ABSTRACT: In this work, a new process is explored for the bulk densification of light soda ash. Advantages of the new process are that no (crystal) water needs to be evaporated and that a crystalline super dense soda ash is produced at atmospherical conditions. The so-called "mixed-solvent" process is based on the fact that the transition temperature at which monohydrous and anhydrous soda in contact with an aqueous solution are in equilibrium, can be lowered when a second solvent is applied. Continuous double recrystallization experiments were carried out in mixtures of water and ethylene glycol: first, light soda was recrystallized into monohydrate below the transition temperature, then the temperature was raised above the transition temperature, and monohydrate was converted into solid, anhydrous soda with a high bulk density. Values of up to 1400 kg/m3 were measured. Further, a significant amount of chloride was removed from the soda during the two recrystallization steps. The potential industrial applications of the double recrystallization process are described by Oosterhof et al. (patent application no. EP19980203963 19981124, 2000).
Koopman, C., Witkamp, G.J.
Ion exchange extraction during continuous recrystallization of CaSO4 in the phosphoric acid production process: Lanthanide extraction efficiency and CaSO4 particle shape
(2002) Hydrometallurgy, 63 (2), pp. 137-147.
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ABSTRACT: In the HemiDiHydrate (HDH) phosphoric acid production processes, calcium sulfate hemihydrate (HH) is formed from the reaction of phosphate ore with sulfuric acid. In a second step, the HH crystals are recrystallized to calcium sulfate dihydrate (DH, gypsum). With the phosphate ore, impurities enter the production processes. Some of these impurities, such as the lanthanides, mainly end up in the DH crystals. Some impurities, such as aluminum fluoride and lanthanides, not only cause contamination of the DH crystals, but also retard the crystallization and influence the HH and DH particle shapes. By adding ion exchange resin during the continuously operated recrystallization, lanthanides are removed resulting in cleaner DH and phosphoric acid. The simultaneous ion exchange extraction accelerates the recrystallization and can lead to differences in DH particle shape. © 2002 Published by Elsevier Science B.V.
Koopman, C., Witkamp, G.J.
Extraction of heavy metals from industrial phosphoric acid in a transverse flow hollow fiber membrane contactor
(2002) Separation Science and Technology, 37 (6), pp. 1273-1290.
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ABSTRACT: Phosphoric acid is produced mainly in the so-called wet processes, in which phosphate ore reacts with sulfuric acid to form phosphoric acid and calcium sulfate solids. With the phosphate ore, impurities enter the production process. Some of these impurities mainly end up in the product acid, others mainly in the calcium sulfate. The aim is to develop an in-line technique for the removal of impurities from the product acid, and simultaneously avoid their incorporation into the calcium sulfate solids. This paper describes the treatment of industrial phosphoric acid in transverse flow hollow fiber membrane contactors and the feasibility of these contactors for the treatment of a phosphoric acid/calcium sulfate slurry. Mercury, copper, lead, and cadmium were extracted from an industrial phosphoric acid by Cyanex 302 (bis(2,4,4-trimethylpentyl)thiophosphinic acid) in kerosene in a contactor. The permeability was 3 × 10-6 m/sec. With the same contactor, erbium, and dysprosium were extracted by di(2-ethylhexyl)phosphoric acid in kerosene. The permeability was 2-6 × 10-8 m/sec. Experiments had to be terminated, because of leakage of organic phase into the aqueous phase. Vibrations due to pulsation of the tube pumps are thought to be the main reason for this leakage. Problems with respect to organic phase leakage due to e.g., the formation of eddies caused by the transverse flow could not be determined. The feasibility of hollow fiber membrane contactors to remove impurities from the slurries depends strongly on the particle size of the solids and the required pitches to avoid clogging.
Gärtner, R.S., Berends, A.M., Witkamp, G.-J.
Testing calix(4)arenes for the selective removal of aluminum from a pickling bath solution
(2002) Journal of Supramolecular Chemistry, 2 (1-3), pp. 159-162.
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ABSTRACT: For the regeneration of an industrial pickling bath solution by a solvent extraction process different extractants were investigated for their capability to extract Al. The two main components of the pickling bath solution are phosphoric and hydrofluoric acid. This work describes the results of shake experiments with different p-tert-butyl-calix[4]arenes. Their capabilities to extract Al were compared with the results of Alamine 308 and another basic extractant, tetrabutyl-phosphonium-bromide (TBP-Br), that is [(C 4H 7) 4P] +Br -. Due to the low pH and the strong complexation of Al by fluoride ions in the pickling bath solution, no significant extraction was found for all the tested calixarenes. © 2003 Elsevier Ltd. All rights reserved.
Oosterhof, H., Witkamp, G.-J., Van Rosmalen, G.M.
Evaporative crystallization of anhydrous sodium carbonate at atmospheric conditions
(2001) AIChE Journal, 47 (10), pp. 2220-2225.
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ABSTRACT: A new process for the production of superdense anhydrous soda ash uses a mixture of water and a high-boiling second solvent to lower the transition point at which anhydrous (Na2CO3) and monohydrous sodium (Na2CO3·H2O) carbonate are in equilibrium to below the atmospheric boiling point. The stable conditions for anhydrate were first established by measuring the water activiiy in saturated mixtures of water and ethylene glycol. With the results, fed-batch evaporative crystallization experiments were carried out. Both the water activity and the crystallization measurements showed that anhydrous soda was stable in boiling mixtures containing more than 22.5 wt. % ethylene glycol (on a sah-free basis). A subsequent continuous evaporative crystallization experiment produced anhydrous soda ash with a bulk density of 1,550 kg/m3, which is substantially higher than that of any other atmospherically crystallized soda.
Berends, A.M., Witkamp, G.-J.
Removal of aluminum from pickling bath liquids by tertiary and quaternary amine extractants
(2001) Solvent Extraction and Ion Exchange, 19 (3), pp. 473-490.
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ABSTRACT: In this work, several extractants and solvents have been investigated for the selective removal of aluminum from a pickling bath, containing HF and H3PO4 as its main active components, each at a concentration of 0.01-0.30 M. The final aim of the research is to increase the lifetime of the pickling bath, resulting in reduced operating costs, in a decreased environmental burden, and in a more constant and better pickling performance. Several tertiary amines and one quaternary amine salt have been examined as extractants, Shellsol D70, paraffine and Marlowtherm S have been examined as solvents and Exxal 13 has been examined as a modifier. None of the aluminum extractions were completely selective as phosphorus was co-extracted; selectivities obtained were 0.16-1.1. Aggregation took place in many shake tests, but adding Exxal 13 to the organic phase decreased the aggregation in most cases. Of the solvents tested, Shellsol D70 showed the lowest aggregation. The best conditions for SLM were found to be 1.0M Alamine 308/Alamine 336 with 50 g/1 Exxal 13. In almost all shake tests, [Al]: [P] ≈ I : 1.3-1.9 in the organic phase.
Thiering, R., Hofland, G., Foster, N., Witkamp, G.-J., Van de Wielen, L.
Carbon dioxide induced soybean protein precipitation: Protein fractionation, particle aggregation, and continuous operation
(2001) Biotechnology Progress, 17 (3), pp. 513-521.
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ABSTRACT: A novel protein fractionation technique using a volatile electrolyte has been developed. Carbon dioxide was used to isoelectrically precipitate 80% and 95% pure glycinin and β-conglycinin fractions from soybean isolate. The protein fractions precipitated as primary particles 0.2-0.3 μm in diameter, which under optimum conditions may be recovered as aggregates up to 500 μm in diameter. The dependency of protein fractionation efficiency on aggregate settling rates has been demonstrated. The isoelectric points of the two main soybean fractions, glycinin and β-conglycinin, were calculated to be pH 5.2 and 4.95, respectively. Solution pH was accurately controlled by pressure in the isoelectric pH range of the different soybean protein fractions, and a pH "overshoot" was eliminated. Volatile electrolyte technology was also applied to a Continuous process in order to eliminate the particle recovery concerns associated with batch precipitation and to demonstrate the potential for scale-up. Glycinin was effectively recovered on-line (94% glycinin recovery) with a purity approaching that of the batch process (95%).
Thiering, R., Hofland, G., Foster, N., Witkamp, G.-J., Van De Wielen, L.
Fractionation of soybean proteins with pressurized carbon dioxide as a volatile electrolyte
(2001) Biotechnology and Bioengineering, 73 (1), pp. 1-11.
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ABSTRACT: Fractionation of specific proteins from plant material is a complex and involved science, yet pure protein extracts are in high demand by a wide range of food and pharmaceutical industries. In this study carbon dioxide has been used as a volatile electrolyte to isoelectrically precipitate two major protein constituents of soybean. Carbon dioxide was shown to be effective in purifying glycinin and β-conglycinin in a three-step process as 95% and 80% concentrated fractions with precipitation yields of 28% and 21%, respectively. Recycling of the mixed precipitate of the intermediary step enables complete separation into the concentrated fractions. Fractionation acidity was precisely controlled by a simple modification of pressure. In addition, the occurrence of a pH overshoot was prevented at any point in the fractionation vessel, as the pH minimum was defined by its equilibrium relationship with carbon dioxide operating pressure. The removal of the glycinin precipitate was an important factor in the purification procedure. The yield of the individual concentrated glycinin and β-conglycinin precipitate fractions was a function of carbon dioxide pressure, extract concentration and, to a much lesser extent, temperature. © 2001 John Wiley & Sons, Inc.
Oosterhof, H., Witkamp, G.-J., Van Rosmalen, G.M.
Antisolvent Crystallization of Anhydrous Sodium Carbonate at Atmospherical Conditions
(2001) AIChE Journal, 47 (3), pp. 602-607.
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ABSTRACT: When antisolvents are applied to crystallize sodium carbonate from aqueous solutions, the transition temperature at which the hydrates are in equilibrium is decreased. Two models proposed can predict the influence of the amount and type of antisolvent on the transition temperature. Only binary data of the water/sodium carbonate system and measured vapor pressures over ternary soda-saturated mixtures of water and antisolvent are needed. To validate the two models, continuous crystallization experiments were carried out at various temperatures using ethylene glycol (EG) and diethylene glycol (DEG) as antisolvent, in varying concentrations. Both models predict the influence of the antisolvent on the transition temperature with good accuracy. Anhydrous soda with bulk densities of up to 950 kg/m3 was crystallized at temperatures as low as 80°C.
Bremere, I., Kennedy, M., Mhyio, S., Jaljuli, A., Witkamp, G.-J., Schippers, J.
Prevention of silica scale in membrane systems: Removal of monomer and polymer silica
(2000) Desalination, 132 (1-3), pp. 89-100.
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ABSTRACT: In reverse osmosis (RO) and nanofiltration silica may precipitate on the membrane surface causing the decline in mass transfer. The appearance of deposits will depend on the different forms of silica, namely monomer, polymer and colloidal present in the feed water and concentrate. Exceeding the solubility of monomer silica is commonly considered to result in the formation of silica scale, which is difficult to remove. As a consequence, deposition of silica scale is prevented avoiding supersaturations, which results in limited conversions with silica rich feedwaters, and/or more recently the addition of antiscalants. The removal of silica in a separate process may be a successful alternative to scale control if the monomer silica concentration is either removed below the solubility level or the remaining silica supersaturation will not cause the deposition in next stage of a RO system. For this purpose, silica deposition from supersaturated solutions (200-700 mg/1) was tested in seeded silica gel (size 63-200 μm) batch experiments (pH = 7, 25°C). Results indicated that monomer silica deposit on seeds and form silica polymers in solution. The formation of latter strongly negatively affects the removal of silica by silica gel seeds. Addition of iron (III) in comparable experiments had a profound effect on removal of monomer and polymer silica. Removal mechanisms most likely include the formation of sparingly soluble iron silicates resulting in un-saturated amorphous silica solution and coagulation of polymer silica. © 2000 Elsevier Science B.V. All rights reserved.
Kersch, C., Van Roosmalen, M.J.E., Woerlee, G.F., Witkamp, G.J.
Extraction of heavy metals from fly ash and sand with ligands and supercritical carbon dioxide
(2000) Industrial and Engineering Chemistry Research, 39 (12), pp. 4670-4672.
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ABSTRACT: This project further develops supercritical fluid extraction as an industrial remediation process for soil and other heavy-metal-contaminated solid materials. In this study, divalent metals such as Zn2+, Cu2+, Pb2+, Cd2+, and Cr3+ are removed from sand and fly ash using CO2. When the solvating power of supercritical CO2 is combined with the metal ion complexing power and selectivity of organic ligands, a clean alternative to conventional liquid-liquid and liquid-solid extraction is obtained. Extraction technologies are required, which not only remove the mobile or total fraction of metals but also maintain the matrix's morphology and structure. In particular, the reuse of fly ash as construction or landfill material becomes possible with the application of supercritical fluid technology. In a Study with spiked sand samples, the effect of pressure, the humidity of the contaminated material, and the use of methanol as the entrainer in CO2 oh the extraction efficiency is investigated. Influences of the type of complexing ligands is studied with both fly ash and sand samples. It is shown that the use of methanol as the entrainer and the humidity have strong effects on the metal extraction.
This project further develops supercritical fluid extraction as an industrial remediation process for soil and other heavy-metal-contaminated solid materials. In this study, divalent metals such as Zn2+, Cu2+, Pb2+, Cd2+, and Cr3+ are removed from sand and fly ash using CO2. When the solvating power of supercritical CO2 is combined with the metal ion complexing power and selectivity of organic ligands, a clean alternative to conventional liquid-liquid and liquid-solid extraction is obtained. Extraction technologies are required, which not only remove the mobile or total fraction of metals but also maintain the matrix's morphology and structure. In particular, the reuse of fly ash as construction or landfill material becomes possible with the application of supercritical fluid technology. In a study with spiked sand samples, the effect of pressure, the humidity of the contaminated material, and the use of methanol as the entrainer in CO2 on the extraction efficiency is investigated. Influences of the type of complexing ligands is studied with both fly ash and sand samples. It is shown that the use of methanol as the entrainer and the humidity have strong effects on the metal extraction.
Boerlage, Ś.F.E., Kennedy, M.D., Bremere, I., Witkamp, G.J., Van Der Hoek, J.P., Schippers, J.C.
Stable barium sulphate supersaturation in reverse osmosis
(2000) Journal of Membrane Science, 179 (1-2), pp. 53-68.
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ABSTRACT: A RO pilot plant operated without antiscalant addition at 85% recovery with no scaling, although the concentrates were significantly supersaturated with barium sulphate. Stable supersaturation may be due to slow precipitation kinetics which may be retarded or enhanced by organic matter present in RO concentrate. BaSO4 precipitation kinetics; crystal nucleation, measured as induction time, and growth were investigated in batch experiments in RO concentrate and in synthetic concentrate containing (i) no organic matter and (ii) commercial humic acid. Supersaturation appeared to control induction time. Induction time decreased more than 36 times with a recovery increase from 80 to 90%, corresponding to a supersaturation of 3.1 and 4.9, respectively. Organic matter in 90% RO concentrate did not prolong induction time (5.5 h). Whereas, commercial humic acid extended induction time in 90% synthetic concentrate to >200 h. This was most likely due to growth inhibition as growth rates determined by seeded growth were reduced by a factor six. In comparison, growth rates were retarded only 2.5 times by organic matter in RO concentrate. However, growth rates measured for 80 and 90% RO concentrate were significant and not likely to limit BaSO4 scaling. Results indicate that the nucleation rate expressed as induction time is governing the occurrence of scaling. (C) 2000 Elsevier Science B.V.
A RO pilot plant operated without antiscalant addition at 85% recovery with no scaling, although the concentrates were significantly supersaturated with barium sulphate. Stable supersaturation may be due to slow precipitation kinetics which may be retarded or enhanced by organic matter present in RO concentrate. BaSO4 precipitation kinetics; crystal nucleation, measured as induction time, and growth were investigated in batch experiments in RO concentrate and in synthetic concentrate containing (i) no organic matter and (ii) commercial humic acid. Supersaturation appeared to control induction time. Induction time decreased more than 36 times with a recovery increase from 80 to 90%, corresponding to a supersaturation of 3.1 and 4.9, respectively. Organic matter in 90% RO concentrate did not prolong induction time (5.5 h). Whereas, commercial humic acid extended induction time in 90% synthetic concentrate to >200 h. This was most likely due to growth inhibition as growth rates determined by seeded growth were reduced by a factor six. In comparison, growth rates were retarded only 2.5 times by organic matter in RO concentrate. However, growth rates measured for 80 and 90% RO concentrate were significant and not likely to limit BaSO4 scaling. Results indicate that the nucleation rate expressed as induction time is governing the occurrence of scaling.
Koopman, C., Witkamp, G.J.
Extraction of lanthanides from the phosphoric acid production process to gain a purified gypsum and a valuable lanthanide by-product
(2000) Hydrometallurgy, 58 (1), pp. 51-60.
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ABSTRACT: In the HemiDiHydrate (HDH) phosphoric acid production processes, calcium sulfate hemihydrate (HH) is formed from the reaction of fluoroapatite ore with sulfuric acid, after which it is recrystallized into calcium sulfate dihydrate (DH, gypsum). Some impurities from the feedstock are incorporated in the HH during the first reaction and finally end up mainly in the sparingly soluble gypsum. By introducing ion exchange resin during the phosphoric acid-mediated recrystallization, lanthanides that are dissolved from the HH can be removed from the acid before they become incorporated again in the gypsum. With 250 g resin/kg phosphoric acid slurry, lanthanides were removed to up to 53% of the input. The resulting decrease of the lanthanide concentration in the gypsum is lower, up to 34%. The extraction efficiency is influenced by the recrystallization reaction. Lanthanides that are most readily taken up by the gypsum are extracted least. Although the sulfonic acid resin has a preference for the trivalent lanthanides, calcium ions are also extracted.
Vaessen, R.J.C., Van Der Ham, F., Witkamp, G.J.
Eutectic freeze crystallization using CO2 clathrates
(2000) Annals of the New York Academy of Sciences, 912, pp. 483-495.
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ABSTRACT: Highly soluble salts can be separated from aqueous solutions by eutectic freeze crystallization (EFC). This technique delivers significant energy savings in comparison with evaporative crystallization. The eutectic temperature can be raised by crystallizing CO2 clathrates instead of normal ice. Application of this process is especially efficient for salt solutions with eutectic points at low temperatures, such as CaCl2 (-55°C). In this work the shift of the eutectic point is predicted by use of a model for NaCl and CaCl2 solutions. Experiments are executed under eutectic conditions, with these substances proving the feasibility of the eutectic clathrate freezing process. Energy calculations show that by using eutectic clathrate crystallization instead of regular EFC the electric energy consumption ran be reduced by 32%.
Breembroek, G.R.M., Witkamp, G.J., Van Rosmalen, G.M.
Design and testing of an emulsion liquid membrane pilot plant
(2000) Separation Science and Technology, 35 (10), pp. 1539-1571.
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ABSTRACT: An emulsion liquid membrane (ELM) extraction rotating disc contactor (RDC) column with auxiliary equipment has been designed and tested. An ELM spray column was designed as well. ELM is a suitable technique for the removal of heavy metal ions from waste or process streams. However, no design rules are available yet. This paper proposes and verifies a design procedure based on solvent extraction methods. The equipment was designed to reduce the 100 ppm cadmium concentration in a 90 L/h feed stream to 5% of its initial value, and to achieve a concentration factor of at least 12.5 in the strip phase. Trilaurylamine (1%) in kerosene was used as the extractant solution. The RDC column diameter was 70 mm and its designed height was 2.2 m. The spray column had a diameter of 50 mm and a designed height of 4.2 m. Both columns were constructed from five separate parts of 1 m height each to obtain the necessary flexibility. Experiments showed a reduction of the cadmium content down to 1% of the initial value and a concentration factor of 14 with the RDC. The efficiency of the spray column experiment was 50%. The rotor speed and the hold up in the RDC had to be kept lower (0.75 and 0.55 times, respectively) than the design values to avoid entrainment of the smallest drops with the feed phase. The validity of the models used in the design was assessed by inserting the actual experimental conditions in the design equations. This resulted in a good coincidence of the actual and calculated characteristic drop velocity, a good coincidence of most mass transfer coefficients, and a reasonable estimation of the number of equilibrium stages. The auxiliary equipment, comprising among others an electrostatic emulsion splitter, operated as designed at optimal conditions. The splitter proved to be critical at smaller emulsion droplet sizes. It can be concluded that design methods for a solvent extraction column are suitable for ELM.
An emulsion liquid membrane (ELM) extraction rotating disc contactor (RDC) column with auxiliary equipment has been designed and tested. An ELM spray column was designed as well. ELM is a suitable technique for the removal of heavy metal ions from waste or process streams. However, no design rules are available yet. This paper proposes and verifies a design procedure based on solvent extraction methods. The equipment was designed to reduce the 100 ppm cadmium concentration in a 90 L/h feed stream to 5% of its initial value, and to achieve a concentration factor of at least 12.5 in the strip phase. Trilaurylamine (1%) in kerosene was used as the extractant solution. The RDC column diameter was 70 mm and its designed height was 2.2 m. The spray column had a diameter of 50 mm and a designed height of 4.2 m. Both columns were constructed from five separate parts of 1 m height each to obtain the necessary flexibility. Experiments showed a reduction of the cadmium content down to 1% of the initial value and a concentration factor of 14 with the RDC. The efficiency of the spray column experiment was 50%. The rotor speed and the hold up in the RDC had to be kept lower (0.75 and 0.55 times, respectively) than the design values to avoid entrainment of the smallest drops with the feed phase. The validity of the models used in the design was assessed by inserting the actual experimental conditions in the design equations. This resulted in a good coincidence of the actual and calculated characteristic drop velocity, a good coincidence of most mass transfer coefficients, and a reasonable estimation of the number of equilibrium stages. The auxiliary equipment, comprising among others an electrostatic emulsion splitter, operated as designed at optimal conditions. The splitter proved to be critical at smaller emulsion droplet sizes. It can be concluded that design methods for a solvent extraction column are suitable for ELM.
Hofland, G.W., De Rijke, A., Thiering, R., Van Der Wielen, L.A.M., Witkamp, G.-J.
Isoelectric precipitation of soybean protein using carbon dioxide as a volatile acid
(2000) Journal of Chromatography B: Biomedical Sciences and Applications, 743 (1-2), pp. 357-368.
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ABSTRACT: A novel process is presented for the isoelectric precipitation of soy protein, using carbon dioxide as a volatile acid. By contacting a soy meal extract with pressurized carbon dioxide, the solution pH was decreased to the isoelectric region of the soy proteins. Complete precipitation of the precipitable soy proteins could be achieved for protein concentrations up to 40 g/l at pressures less than 50 bar. Isoelectric precipitation with a volatile acid enabled accurate control of the solution pH by pressure and eliminated the local pH overshoot, usual in conventional precipitation techniques. The advantage of the improved precipitation control was reflected by the morphology of the precipitate particles. Protein aggregates formed by CO2 were perfectly spherical whereas protein precipitated by sulfuric acid had an irregular morphology. The influence of process variables to control particle size is discussed. (C) 2000 Elsevier Science B.V.
Zijlema, T.G., Geertman, R.M., Witkamp, G.-J., van Rosmalen, G.M., De Graauw, J.
Antisolvent crystallization as an alternative to evaporative crystallization for the production of sodium chloride
(2000) Industrial and Engineering Chemistry Research, 39 (5), pp. 1330-1337.
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ABSTRACT: A comparison has been made between the antisolvent crystallization of NaCl with diisopropylamine and the traditional four-effect evaporative crystallization of NaCl. Calculations demonstrated that for a 1 Mton/year salt production plant with an on-site integrated steam power plant the reduction in energy costs can be 29% if antisolvent crystallization is applied. The estimated fixed capital costs, however, are 8-55% higher for the antisolvent crystallization of NaCl, depending on the process configuration used. As a result of the higher fixed capital costs, the costs in the production of NaCl are lower for the four-effect evaporative crystallization route in all cases.
A comparison has been made between the antisolvent crystallization of NaCl with diisopropyl-amine and the traditional four-effect evaporative crystallization of NaCl. Calculations demonstrated that for a 1 Mton/year salt production plant with an on-site integrated steam power plant the reduction in energy costs can be 29% if antisolvent crystallization is applied. The estimated fixed capital costs, however, are 8-55% higher for the antisolvent crystallization of NaCl, depending on the process configuration used. As a result of the higher fixed capital costs, the costs in the production of NaCl are lower for the four-effect evaporative crystallization route in all cases.
Koopman, C., Witkamp, G.J.
Removal of heavy metals by solvent extraction and supported solvent extraction during a recrystallization step in the phosphoric acid production process
(1999) Proceedings of the Engineering Foundation Conference, pp. 327-335.
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ABSTRACT: During the production of phosphoric acid from phosphate ore and sulfuric acid, large amounts of calcium sulfate are formed, in which impurities from the feedstock are incorporated. To use the calcium sulfate in, for example, the building industry, a lower concentration of impurities is desired. Mercury, copper, lead, and cadmium were extracted from clear industrial recrystallization acid (0.8-3.9 mol/kg H3PO4, 0.2-0.5 mol/kg H2SO4) by supported solvent extraction with the extracting agent Cyanex 302 in kerosene in a transverse flow hollow fiber module. The permeability for the mercury ion was 1.4·10-6 m/s, whereas that for the copper ion was calculated to be 1.5·10-6 m/s. Cadmium, lead, and copper were extracted during the recrystallization of calcium sulfate hemihydrate to dihydrate, an existing step within the phosphoric acid production process, by solvent extraction with the same extracting agent. The concentrations of cadmium and zinc in the newly formed calcium sulfate were proven to be decreased. Unfortunately, concentrations of mercury and lead were too low for analysis.
Kersch, Chr., Woerlee, G.F., Witkamp, G.J.
Extraction of heavy metals from solid matrices with ligands and supercritical carbon dioxide
(1999) Proceedings of the Engineering Foundation Conference, pp. 161-165.
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ABSTRACT: The extraction efficiency of heavy metals from sand matrices with supercritical carbon dioxide is influenced by a number of process parameters. Cyanex 302 results in efficiencies of greater than 50% for most of the metals. The amount of Cd extracted with Aliquat 336, in combination with NaCl solution, was significantly greater than for all metals tested. (Di-2(ethylhexyl)-phosphoric acid)and (di-isooctylphosphinic acid) are most effective for Zn extraction. In general, Hg was removed from the matrices entirely. High pressure enhances the complex solubility in CO2, leading to more effective extraction. Highest extraction efficiencies were obtained at water concentrations in the range of 5 wt% to 10 wt%, under which 99% Cd and Cu extraction is obtained.
Zijlema, T.G., Hollman, R.J.A.J., Witkamp, G.J., Van Rosmalen, G.M.
The production of pure NaCl by the antisolvent crystallisation of NaCl · 2H2O and a consecutive recrystallisation step
(1999) Journal of Crystal Growth, 198-199 (PART I), pp. 789-795.
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ABSTRACT: NaCl · 2H2O crystals formed by antisolvent crystallisation with N,N-dimethylisopropylamine (DMiPA), were recrystallised batchwise into NaCl at 0.2°C and 0.5°C in pure brines and in brines containing 5 wt% DMiPA. In all experiments the recrystallisation brought about a strong purification of the solid phase. The average DMiPA concentration in the NaCl · 2H2O crystals was approximately 1000 ppm, whereas the DMiPA concentration in the NaCl product was between 1 and 6 ppm. Both the DMiPA concentration in the mother liquor and the recrystallisation temperature influenced the average NaCl crystal size and the rate at which the recrystallisation took place significantly. © 1999 Elsevier Science B.V. All rights reserved.
Van Der Ham, F., Witkamp, G.J., De Graauw, J., Van Rosmalen, G.M.
Eutectic freeze crystallization simultaneous formation and separation of two solid phases
(1999) Journal of Crystal Growth, 198-199 (PART I), pp. 744-748.
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ABSTRACT: Eutectic freeze crystallization (EFC) separates aqueous inorganic solutions into pure water and pure salt. By operating at the eutectic point, ice and salt can be formed simultaneously as two separate phases. Two aqueous systems were investigated in batch and continuous crystallization experiments: copper sulfate (eutectic temperature 271 K) and mono-ammonium phosphate (269 K). Below the eutectic temperature, ice can be formed without any salt formation by seeding with ice seeds and solely salt is formed by seeding with salt crystals. When however, the solution is seeded with both salt and ice crystals, two distinct solid phases are formed: when the stirrer is turned off, ice rises and salt settles. This shows that EFC separates aqueous solutions into ice and salt as two distinct phases. Based on these results, a 151 cooled disk column crystallizer (CDCC) has been built, designed to crystallize and separate both the solids simultaneously in a single apparatus. © 1999 Elsevier Science B.V. All rights reserved.
Oosterhof, H., Geertman, R.M., Witkamp, G.J., Van Rosmalen, G.M.
The growth of sodium nitrate from mixtures of water and isopropoxyethanol
(1999) Journal of Crystal Growth, 198-199 (PART I), pp. 754-759.
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ABSTRACT: The growth of sodium nitrate was studied in a microscopic setup; crystals were nucleated and grown from mixtures of water and isopropoxyethanol (IPE). The phase diagram of the IPE/water system saturated with sodium nitrate and the solubility of NaNO3 in aqueous mixtures with IPE were determined. The growth rate was found to be dependent linearly on the concentration difference (c-c*). Mass transfer constant kD decreased with increasing weight fraction of isopropoxyethanol in the mixture and was predicted accurately from density, viscosity and solubility data only. No changes in crystal morphology were observed. © 1999 Elsevier Science B.V. All rights reserved.
Hofland, G.W., Van Es, M., Van Der Wielen, L.A.M., Witkamp, G.-J.
Isoelectric precipitation of casein using high-pressure CO2
(1999) Industrial and Engineering Chemistry Research, 38 (12), pp. 4919-4927.
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ABSTRACT: High-pressure CO2 was used as a recyclable acid for the isoelectric precipitation of casein. Measurement of the pH during the high-pressure process allowed the comparison of the process with conventional precipitation using sulfuric acid. A simple model was made up to calculate the pH in complex aqueous solutions pressurized with CO2. It was established that the isoelectric point (pH 4.6) could not be reached with CO2, unless the milk was diluted. Nevertheless, high precipitation yields could be obtained with this process. Still, it was found that the precipitation is mainly caused by the decrease in pH. The removal of calcium phosphate appeared to be complicated, probably because of precipitation of calcium phosphate in the casein-free solutions after the pressure is released.
Koopman, C., Hoogerwerf, M., Witkamp, G.J.
In-line removal of impurities by ion exchange during a recrystallization step in the phosphoric acid production process
(1999) Proceedings of the TMS Fall Extraction and Processing Conference, 2, pp. 1745-1753.
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ABSTRACT: During the production of phosphoric acid by the HemiDiHydrate process, calcium sulfate dihydrate (DH, gypsum) is formed as a byproduct, which is mainly disposed. Some impurities from the feedstock, like lanthanides and some heavy metals, mainly end up in the gypsum. During the solvent mediated recrystallization of calcium sulfate hemihydrate (HH) to gypsum, an existing step within the HemiDiHydrate production process, the impurities might be removed from the slurry by ion exchange. However, conventional set-ups, like packed beds, cannot be used for the recrystallizing slurry with 200-400 g solids/kg slurry. Lanthanides can be recovered during the recrystallization of calcium sulfate hemihydrate to calcium sulfate dihydrate in industrial recrystallization acid by ion exchange in stirred vessels as well as in the developed transverse flow ion exchange module. However, due to the relatively small amounts of ion exchange resin per kg of slurry (50 g resin/(kg slurry) for the stirred vessels, and 20 g resin/(kg slurry) for the module), the extraction efficiencies are low (15% for the stirred vessel, and 4% for the module). It should be possible to increase the extraction efficiency by increasing the amount of ion exchange resin per kg of slurry.
Gartner, Robert S., Berends, Anke M., Witkamp, Geert-Jan
Extraction of aluminum from a pickling bath solution by liquid-liquid extraction with calixarenes
(1999) Proceedings of the Engineering Foundation Conference, pp. 315-326.
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ABSTRACT: The selective aluminum extraction by 3 different calixarenes (p-tert-butyl-calix[4]arene-tetra-2-acetic-acid-ethyl-ester, p-tert-butyl-calix[4]arene-tetra-2-acetic-acid and p-tert-butyl-calix-[4]arene-di-2-acetic-acid-ethyl-ester) from an industrial pickling bath solution was studied. The pickling bath solution contained hydrofluoric and phosphoric acid as its main components. The aluminum removal was not successful and also no significant extraction of trace metals present was observed.
Zijlema, T.G., Witkamp, G.-J., Van Rosmalen, G.M.
Specific heats and enthalpies of mixing of amine-H2O and amine-H2O-NaCl mixtures
(1999) Journal of Chemical and Engineering Data, 44 (6), pp. 1335-1337.
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ABSTRACT: Specific heats of mixtures of dimethylisopropylamine (N,N-dimethyl-2-propanamine) or diisopropylamine (N-(1-methylethyl)-2-propanamine) and water and of dimethylisopropylamine and water saturated with NaCl were measured in a temperature range from 272 to 280 K at atmospheric pressure. The specific heats of the three systems all obtained maximum values in the amine weight fraction range (salt free) of 0.1 to 0.4. The enthalpies of mixing of dimethylisopropylamine or diisopropylamine and water were determined as a function of the amine concentration in the mixture. The mixing of water and the amines was strongly exothermic. The highest measured enthalpies of mixing per gram of mixture were -105 J·g-1 for dimethylisopropylamine-H2O at an amine weight fraction of 0.49 and -81 J·g-1 for diisopropylamine-H2O at an amine weight fraction of 0.60.
Bremere, I., Kennedy, M., Michel, P., van Emmerik, R., Witkamp, G.J., Schippers, J.
Controlling scaling in membrane filtration systems using a desupersaturation unit
(1999) Desalination, 124 (1-3), pp. 51-62.
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ABSTRACT: Scaling in reverse osmosis (RO) and nanofiltration (NF) systems is generally controlled by limiting the conversion and/or the addition of antiscalants. An alternative approach might be the desupersaturation of membrane concentrate before e.g. the last stage of an RO and/or NF system. A desupersaturation unit (DU) is aimed at reducing the degree of supersaturation in membrane concentrate stream by forced precipitation of sparingly soluble inorganic compounds on seed crystals. Barium sulfate precipitation was examined in a laboratory scale (DU) using supersaturated synthetic (no organic matter) and natural RO and NF concentrates. Effective barium removal for at least 100 h was observed in the case of synthetic concentrate. Early breakthrough of barium sulfate crystallization occurred in NF concentrate. This was attributed to the adsorption of organic matter (TOC = 22 mg/l) and subsequent poisoning of barium sulfate seed crystals. Two RO concentrates from surface water treatment pilot plants were compared. Barium sulfate removal was not affected (100 h) by organic matter (TOC = 12 mg/l) in River Rhine water pretreated by ultrafiltration. However, break-through was observed from River Rhine water with organic matter (TOC = 8 mg/l) pretreated by ozonation. Irreversible poisoning of seed crystals was attributed to adsorption of organic compounds, e.g. low molar mass acids produced by ozone pretreatment of RO feedwater. Inactivated barium sulfate crystals were restored by backwashing with acidified (pH = 2) water.
Scaling in reverse osmosis (RO) and nanofiltration (NF) systems is generally controlled by limiting the conversion and/or the addition of antiscalants. An alternative approach might be the desupersaturation of membrane concentrate before e.g. the last stage of an RO and/or NF system. A desupersaturation unit (DU) is aimed at reducing the degree of supersaturation in membrane concentrate stream by forced precipitation of sparingly soluble inorganic compounds on seed crystals. Barium sulfate precipitation was examined in a laboratory scale (DU) using supersaturated synthetic (no organic matter) and natural RO and NF concentrates. Effective barium removal for at least 100 h was observed in the case of synthetic concentrate. Early break-through of barium sulfate crystallization occurred in NF concentrate. This was attributed to the adsorption of organic matter (TOC = 22 mg/l) and subsequent poisoning of barium sulfate seed crystals. Two RO concentrates from surface water treatment pilot plants were compared. Barium sulfate removal was not affected (100 h) by organic matter (TOC = 12 mg/l) in River Rhine water pretreated by ultrafiltration. However, break-through was observed from River Rhine water with organic matter (TOC = 8 mg/l) pretreated by ozonation. Irreversible poisoning of seed crystals was attributed to adsorption of organic compounds, e.g. low molar mass acids produced by ozone pretreatment of RO feedwater. Inactivated barium sulfate crystals were restored by backwashing with acidified (pH = 2) water.
Zijlema, T.G., Witkamp, G.-J., Van Rosmalen, M.
Liquid-liquid and solid-liquid equilibria of 2-isopropoxyethanol-H2O-NaCl mixtures
(1999) Journal of Chemical and Engineering Data, 44 (6), pp. 1338-1340.
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ABSTRACT: Liquid-liquid equilibria experiments demonstrated that mixtures of 2-isopropoxyethanol and water saturated with NaCl are partially miscible. The lower critical solution temperature was estimated to be 29.2°C at a 2-isopropoxyethanol concentration of 0.399 (mIPE/(mIPE + mH(2)O)). Solid-liquid equilibria experiments showed that the solubility of NaCl in water is reduced significantly by the presence of 2-isopropoxyethanol. As in pure water, the NaCl solubility in 2-isopropoxyethanol-H2O mixtures increases weakly with temperature.
De Vreugd, C.H., Ter Horst, J.H., Durville, P.F.M., Witkamp, G.J., Van Rosmalen, G.M.
Adsorption behaviour of polyelectrolytes on calcium fluoride. Part I: Influence of the pH and the ionic strength on the adsorption isotherms
(1999) Colloids and Surfaces A: Physicochemical and Engineering Aspects, 154 (3), pp. 259-271.
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ABSTRACT: The adsorption behaviour of weak polyelectrolytes onto CaF2 crystals has been investigated to support the research on the mechanism of growth retardation. Adsorption isotherms and surface concentration plateau values of three kinds of poly(phosphino)acrylate, a polyacrylate and a polymaleate were determined at different pH values in pure water and at a higher ionic strength. It was found that the surface concentration plateau values decrease with decreasing pH. The addition of an indifferent salt makes the polyelectrolytes more flexible due to partial screening of the polyelectrolyte charge.
The adsorption behaviour of weak polyelectrolytes onto CaF2 crystals has been investigated to support the research on the mechanism of growth retardation. Adsorption isotherms and surface concentration plateau values of three kinds of poly(phosphino)acrylate, a polyacrylate and a polymaleate were determined at different pH values in pure water and at a higher ionic strength. It was found that the surface concentration plateau values decrease with decreasing pH. The addition of an indifferent salt makes the polyelectrolytes more flexible due to partial screening of the polyelectrolyte charge.
Ter Horst, J.H., Wong Fong Sang, K.E., De Vreugd, C.H., Geertman, R.M., Witkamp, G.J., Van Rosmalen, G.M.
Adsorption behaviour of polyelectrolytes on calcium fluoride. Part II: Molecular modeling of the adsorption behaviour
(1999) Colloids and Surfaces A: Physicochemical and Engineering Aspects, 154 (3), pp. 273-284.
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ABSTRACT: Molecular modeling techniques were used to find an explanation for the observed adsorption behaviour of polyelectrolytes on CaF2. The adsorption energies of polyacrylate (PA) and polymaleate (PM) on calcium fluoride (CaF2) were calculated at different pH values. It was found that the adsorption energy becomes less negative at higher pH values, indicating that the surface concentration plateau value of the polyelectrolytes decreases with increasing pH. This finding is in agreement with the observations.
Molecular modeling techniques were used to find an explanation for the observed adsorption behaviour of polyelectrolytes on CaF2. The adsorption energies of polyacrylate (PA) and polymaleate (PM) on calcium fluoride (CaF2) were calculated at different pH values. It was found that the adsorption energy becomes less negative at higher pH values, indicating that the surface concentration plateau value of the polyelectrolytes decreases with increasing pH. This finding is in agreement with the observations.
Oosterhof, H., Witkamp, G.J., Van Rosmalen, G.M.
Some antisolvents for crystallisation of sodium carbonate
(1999) Fluid Phase Equilibria, 155 (2), pp. 219-227.
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ABSTRACT: The phase behaviour of ten aqueous mixtures of an alkanediol saturated with sodium carbonate was studied: between 40 and 90°C the solubility of sodium carbonate was measured in mixtures with different alkane-diol to water ratios. Six systems featured phase separation: polyethylene-glycol 200, polyethylene-glycol 400, tri-ethylene-glycol, 1,2-butanediol, 1,3-butanediol and 1,4-butanediol. Four antisolvents were fully miscible: ethylene glycol, di-ethylene-glycol, glycerol, and 1,2-propanediol. Solubility measurements showed that di-ethylene-glycol is the best antisolvent: sodium carbonate recoveries of 99% are achievable.
The phase behaviour of ten aqueous mixtures of an alkanediol saturated with sodium carbonate was studied: between 40 and 90°C the solubility of sodium carbonate was measured in mixtures with different alkane-diol to water ratios. Six systems featured phase separation: polyethylene-glycol 200, polyethylene-glycol 400, tri-ethylene-glycol, 1,2-butanediol, 1,3-butanediol and 1,4-butanediol. Four antisolvents were fully miscible: ethylene glycol, di-ethylene-glycol, glycerol, and 1,2-propanediol. Solubility measurements showed that di-ethylene-glycol is the best antisolvent: sodium carbonate recoveries of 99% are achievable.
Koopman, C., Witkamp, G.J., Van Rosmalen, G.M.
Removal of heavy metals and lanthanides from industrial phosphoric acid process liquors
(1999) Separation Science and Technology, 34 (15), pp. 2997-3008.
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ABSTRACT: To diminish the discharge of heavy metals and lahthanides by the phosphoric acid industry, these impurities have to be removed from the mother liquor before their incorporation in the gypsum crystals. This can best be achieved by means of solvent extraction or ion exchange during the recrystallization of hemihydrate to dihydrate gypsum. Various commercial carriers and two ion-exchange resins were screened for their efficiency and selectivity. Light and heavy lanthanide ions are extracted from the recrystallization acid by didodecylnaphthalenesulfonic acid (Nacure 1052) and di-(2-ethylhexyl)phosphoric acid (D2EHPA), and the heavy-metal ions by bi:s(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301) and by bis(2,4,4-4-trimethylpentyl)monothiophosphinic acid (Cyanex 302). Mercury is also extracted by the an- ion carriers tri(C8-C10)amine (Alamine 33-65 and tri(C8-C10) monomethyl ammonium-chloride (Aliquat 336). Both Dowex C-500 and Amberlite IR-120 extract lanthanide and heavy-metal ions. Unfortunately, D2EHPA, Nacure 1052, and the two ion-exchange resins also show affinity for ions present in much higher concentrations, like calcium or iron ions.
To diminish the discharge of heavy metals and lanthanides by the phosphoric acid industry, these impurities have to be removed from the mother liquor before their incorporation in the gypsum crystals. This can best be achieved by means of solvent extraction or ion exchange during the recrystallization of hemihydrate to dihydrate gypsum. Various commercial carriers and two ion-exchange resins were screened for their efficiency and selectivity. Light and heavy lanthanide ions are extracted from the recrystallization acid by didodecylnaphthalenesulfonic acid (Nacure 1052) and di-(2-ethylhexyl)phosphoric acid (D2EHPA), and the heavy-metal ions by bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301) and by bis(2,4,4-trimethylpentyl)monothiophosphinic acid (Cyanex 302). Mercury is also extracted by the anion carriers tri(C8-C10)amine (Alamine 336) and tri(C8-C10) monomethyl ammonium chloride (Aliquat 336). Both Dowex C-500 and Amberlite IR-120 extract lanthanide and heavy-metal ions. Unfortunately, D2EHPA, Nacure 1052, and the two ion-exchange resins also show affinity for ions present in much higher concentrations, like calcium or iron ions.
Berends, A.M., Witkamp, G.J., Van Rosmalen, G.M.
Extraction of aluminum from a pickling bath with supported liquid membrane extraction
(1999) Separation Science and Technology, 34 (6-7), pp. 1521-1543.
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ABSTRACT: Large amounts of waste are produced yearly in the galvanic and chemical surface treatment industry. Bath liquids used in the various processes lose their function due to contamination. The spent bath liquids have to be replaced and treated prior to disposal, leading to high costs and a high environmental burden. In this paper, a proposed solution to the problem is investigated: the selective removal of the contaminant with supported liquid membrane extraction. The extraction of aluminum, a contaminant at high concentrations, from a pickling bath liquid with hydrofluoric acid and phosphoric acid as its main components has been carried out with the basic extractants Alamine 308 and Alamine 336 in a fiat sheet-supported liquid membrane setup. Aluminum transport rates were obtained in the order of 10- 6-10-5 mol/(m2·s), which are normal values for this technique. The extraction was not completely selective as dissolved phosphorus was coextracted. In all experiments, precipitation took place on the surface of the liquid membrane and in the bulk of the strip phase. Increasing the stripping alkalinity from pH = 8 to pH = 13 reduced the amount of precipitation in the bulk of the strip phase but caused a substantial decrease in the aluminum flux. The precipitation prevents industrial application of the systems investigated.
Large amounts of waste are produced yearly in the galvanic and chemical surface treatment industry. Bath liquids used in the various processes lose their function due to contamination. The spent bath liquids have to be replaced and treated prior to disposal, leading to high costs and a high environmental burden. In this paper, a proposed solution to the problem is investigated: the selective removal of the contaminant with supported liquid membrane extraction. The extraction of aluminum, a contaminant at high concentrations, from a pickling bath liquid with hydrofluoric acid and phosphoric acid as its main components has been carried out with the basic extractants Alamine 308 and Alamine 336 in a flat sheet-supported liquid membrane setup. Aluminum transport rates were obtained in the order of 10-6-10-5 mol/(m2·s), which are normal values for this technique. The extraction was not completely selective as dissolved phosphorous was coextracted. In all experiments, precipitation took place on the surface of the liquid membrane and in the bulk of the strip phase. Increasing the stripping alkalinity from pH = 8 to pH = 13 reduced the amount of precipitation in the bulk of the strip phase but caused a substantial decrease in the aluminum flux. The precipitation prevents industrial application of the systems investigated.
Bremere, I., Kennedy, M.D., Johnson, A., Van Emmerik, R., Witkamp, G.-J., Schippers, J.C.
Increasing conversion in membrane filtration systems using a desupersaturation unit to prevent scaling
(1998) Desalination, 119 (1-3), pp. 199-204.
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ABSTRACT: A desupersaturation unit (DU), placed between the stages of either RO or NF systems is aimed at reducing the degree of supersaturation in the concentrate stream thus preventing membrane scaling in the last stage of a membrane filtration system while allowing conversion to be maximized up to design limits (>90%). Barium sulfate desupersaturation in an up-flow fixed bed reactor was demonstrated for ca. 200 h (Concentrate A). However, barium removal in the DU was shown to be source dependent and early break-through of the DU occurred with Concentrate B after ca. 30 h. Calculations showed that barium sulfate deposition in the DU was affected by natural organic matter (NOM). Blocking of seed crystal surface by rapid adsorption of certain NOM fractions hindered crystal growth and was believed to be the main reason for break-through in the DU. Recycling of these naturally occurring organic molecules as 'natural antiscalants' to maximize the conversion of RO (NF) systems may be possible if they can be isolated and characterized.
A desupersaturation unit (DU), placed between the stages of either RO or NF systems is aimed at reducing the degree of supersaturation in the concentrate stream thus preventing membrane scaling in the last stage of a membrane filtration system while allowing conversion to be maximized up to design limits (>90%). Barium sulfate desupersaturation in an up-flow fixed bed reactor was demonstrated for ca. 200 h (Concentrate A). However, barium removal in the DU was shown to be source dependent and early break-through of the DU occurred with Concentrate B after ca. 30 h. Calculations showed that barium sulfate deposition in the DU was affected by natural organic matter (NOM). Blocking of seed crystal surface by rapid adsorption of certain NOM fractions hindered crystal growth and was believed to be the main reason for break-through in the DU. Recycling of these naturally occurring organic molecules as `natural antiscalants' to maximize the conversion of RO (NF) systems may be possible if they can be isolated and characterized.
Breembroek, G.R.M., Witkamp, G.J., Van Rosmalen, G.M.
Extraction of cadmium with trilaurylamine-kerosine through a fiat-sheet-supported liquid membrane
(1998) Journal of Membrane Science, 147 (2), pp. 195-206.
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ABSTRACT: Cadmium has been extracted as a chloride complex through a flat-sheet-supported liquid membrane (SLM), using the tertiary amine Alamine 304-1 (mainly trilaurylamine or TLA) in kerosine. The typical permeability of the membrane was 1.1 x 10-6 m s-1. The rate limiting step is diffusion through the membrane. The cadmium loading of the extractant at the feed-membrane interface is high. Trilaurylammonium chloride crystallizes at the surface of the membrane above 0.2 M TLA. This salt blocks the pores and lowers the extraction rate up to a factor of 3. Apart from this blocking effect, the permeability through the membrane is described well with the presented model, using physically realistic parameter values. When the precipitation can be minimized, the system has good potentials for the extraction of cadmium chloride complexes.
Cadmium has been extracted as a chloride complex through a flat-sheet-supported liquid membrane (SLM), using the tertiary amine Alamine 304-1 (mainly trilaurylamine or TLA) in kerosine. The typical permeability of the membrane was 1.1×10-6 m s-1. The rate limiting step is diffusion through the membrane. The cadmium loading of the extractant at the feed-membrane interface is high. Trilaurylammonium chloride crystallizes at the surface of the membrane above 0.2 M TLA. This salt blocks the pores and lowers the extraction rate up to a factor of 3. Apart from this blocking effect, the permeability through the membrane is described well with the presented model, using physically realistic parameter values. When the precipitation can be minimized, the system has good potentials for the extraction of cadmium chloride complexes.
Breembroek, G.R.M., Van Straalen, A., Witkamp, G.J., Van Rosmalen, G.M.
Extraction of cadmium and copper using hollow fiber supported liquid membranes
(1998) Journal of Membrane Science, 146 (2), pp. 185-195.
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ABSTRACT: Copper, cadmium and lead were extracted through a hollow fiber supported liquid membrane with Lix 84-i as copper extractant and Alamine 304-i as extractant for cadmium and lead. The mass transfer rate, expressed as permeability P, was limited by the diffusion through the aqueous stagnant films in the module for copper extraction. A characteristic permeability of 6.9 x 10-6 m s-1 was measured at a flow rate of 0.076 m s-1 through the fibers. The measured permeabilities were compared to generally accepted mass transfer correlations. For a feed flowing on the tube side, these correlations predicted a three times higher permeability than was measured, while at the shell side, the permeabilities predicted from these accepted correlations were up to a factor of 8 lower than the measured ones. The extraction rate of cadmium from chloride solutions was limited by membrane diffusion. At 0.2 M Alamine 304-i, a permeability of 4·10-6 m s-1 was measured. Higher extraction rates were found when cadmium was extracted from chloride-containing mixtures of phosphoric and sulfuric acid. The extraction rate of lead was a factor of 20 lower than that of cadmium. This was due to the fact that the extractant had a lower affinity for lead.
Copper, cadmium and lead were extracted through a hollow fiber supported liquid membrane with Lix 84-i as copper extractant and Alamine 304-i as extractant for cadmium and lead. The mass transfer rate, expressed as permeability P, was limited by the diffusion through the aqueous stagnant films in the module for copper extraction. A characteristic permeability of 6.9×10-6 m s-1 was measured at a flow rate of 0.076 m s-1 through the fibers. The measured permeabilities were compared to generally accepted mass transfer correlations. For a feed flowing on the tube side, these correlations predicted a three times higher permeability than was measured, while at the shell side, the permeabilities predicted from these accepted correlations were up to a factor of 8 lower than the measured ones. The extraction rate of cadmium from chloride solutions was limited by membrane diffusion. At 0.2 M Alamine 304-i, a permeability of 4.10-6 m s-1 was measured. Higher extraction rates were found when cadmium was extracted from chloride-containing mixtures of phosphoric and sulfuric acid. The extraction rate of lead was a factor of 20 lower than that of cadmium. This was due to the fact that the extractant had a lower affinity for lead.
Van Der Ham, F., Witkamp, G.J., De Graauw, J., Van Rosmalen, G.M.
Eutectic freeze crystallization: Application to process streams and waste water purification
(1998) Chemical Engineering and Processing: Process Intensification, 37 (2), pp. 207-213.
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ABSTRACT: Two case studies are presented using eutectic freeze crystallization (EFC) as an alternative for evaporative crystallization: a 7.8 ton day-1 35 w% aqueous sodium nitrate and a 24 ton day-1 12 w% copper sulfate stream. The proposed crystallizer is a cooled disk column crystallizer (CDCC), using indirect cooling for heat transfer. In single stage operation, the formed ice crystals are used to pre-cool the feed stream. A two stage refrigeration unit utilizes the formed ice crystals in the condensation of refrigerant. Expressed as a thermal equivalent energy requirement, EFC requires 1282 kJ kg-1 NaNO3 and 1037 kJ kg-1 CuSO4·5H2O. Compared to conventional multi-step evaporation, the energy reductions are 30% for sodium nitrate and 65% for copper sulfate. © 1998 Elsevier Science S.A. All rights reserved.
Zijlema, T.G., Oosterhof, H., Witkamp, G.J., Van Rosmalen, G.M.
Crystallization of Sodium Chloride with Amines as Antisolvents
(1997) ACS Symposium Series, 667, pp. 230-241.
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ABSTRACT: The suitability of the amines diisopropylamine (DiPA) and dimethylisopropylamine (DMiPA) as antisolvents for the crystallization of sodium chloride from its aqueous solution has been demonstrated. Both amines decreased the sodium chloride solubility substantially. The presence of a two liquid phase area offered the opportunity to separate the amines from the mother liquor after crystallization by a temperature increase. In the two liquid phase area the mutual solubilities of the water and the amines were low, so the separability was good. Continuous crystallization experiments were carried out at temperatures below the liquid-liquid equilibrium line in the single liquid phase area. The product consisted of cubic agglomerated NaCl crystals with maximum primary particle sizes of 10-70 μm.
Van Der Weijden, R.D., Van Der Heijden, A.E., Witkamp, G.J., Van Rosmalen, G.M.
The influence of total calcium and total carbonate on the growth rate of calcite
(1997) Journal of Crystal Growth, 171 (1-2), pp. 190-196.
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ABSTRACT: The influence of total calcium and total carbonate on the growth rate of calcite under seawater-like conditions was studied with a chemostat system. The growth rate increased with increasing calcium concentration, due to a higher supersaturation. At equal supersaturation and similar free activities of calcium and carbonate, the growth rate increased at a higher total carbonate concentration. This increase can be explained by a contribution of bicarbonate to calcite crystal growth.
Kralj, D., Breembroek, G.R.M., Witkamp, G.J., Van Rosmalen, G.M., Brečević, L.
Selective dissolution of copper oxalate using supported liquid membranes
(1996) Solvent Extraction and Ion Exchange, 14 (4), pp. 705-720.
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ABSTRACT: A supported liquid membrane has been used to dissolve selectively copper oxalate from a suspension of copper, calcium and cadmium oxalate, which have low, similar solubilities. 2-Hydroxy-5-nonyl-acetophenone oxime (HX) dissolved in kerosene was used as a carrier for copper transport from the suspension to the stripping solution. A mathematical model of the copper permeation is presented. The model takes into account the dissolution kinetics of CuC2O4·1/2H2O, the diffusion of copper ions through an aqueous stagnant layer, the chemical reaction at the aqueous/membrane interface, and the diffusion of the CuX2 complex in the membrane. The model fits the experimental data well with a unique parameter set, except for the transport from an acetate buffered system, for which a lower rate constant for the reaction at the membrane interface had to be assumed. In a separate set of experiments the dissolution of copper oxalate hemihydrate in water was found to be surface reaction controlled.
Martynowicz, E.T.M.J., Witkamp, G.-J., Van Rosmalen, G.M.
The effect of aluminium fluoride on the formation of calcium sulfate hydrates
(1996) Hydrometallurgy, 41 (2-3), pp. 171-186.
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ABSTRACT: Different phases, hydrates or polymorphs are often developed in mineral ore conversion processes where sparingly soluble salts are formed. Their development not only depends on the operating conditions but also on the specific composition of the ore. In this study the effect of aluminium fluoride, a constituent encountered in fluorapatite rock in varying concentrations, on the formation of calcium sulfate hydrates during phosphoric acid processing is presented. Solubility experiments and continuous crystallization experiments of calcium sulfate hemihydrate (CaSO4 · 1/2H2O, HH) and calcium sulfate dihydrate (CaSO4 · 2H2O, DH) were performed in concentrated phosphoric/sulfuric acid solutions at 75°C and 90°C in the presence of small amounts of aluminium fluoride or hydrogen fluoride. Both AlF3 and HF increase the solubilities of HH and DH via their effect on the activity coefficients of calcium and sulfate. Aluminium fluoride retards the HH and DH growth rate and an AlF3 concentration of 95 mmol (kg solution)-1 increases the calcium sulfate concentration far above the DH solubility line. This leads to DH formation under conditions where normally HH is formed. The presence of aluminium fluoride also results in crystal habit modification and agglomeration of the HH and DH crystals formed.
Martynowicz, E.T.M.J., Liao, L., Witkamp, G.-J., Van Rosmalen, G.M.
The influence of aluminium fluoride in hemi-dihydrate phosphoric acid processes
(1996) Hydrometallurgy, 41 (2-3), pp. 155-170.
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ABSTRACT: Bench-scale continuous crystallization experiments were performed with three different types of phosphate ores in a cascade of bench-scale crystallizers, thus simulating the calcium sulfate hemihydrate (CaSO4·1/2H2O) crystallization section in a two-filter hemi-dihydrate phosphoric acid process. The effect of aluminium fluoride in the system was investigated by the addition of an aluminium salt and the use of ores with different aluminium contents. Aluminium fluoride, which might affect the crystallization by its growth-retarding AIF2- 5 complex, promotes the formation of DH (CaSO4·2H2O) modification and the formation of agglomerates of short crystals, and therefore influences the permeability of the crystal product formed. The aluminium distribution coefficient ([Al] in solid/[Al] in liquid) in calcium sulfate hemihydrate decreases strongly with increasing aluminium concentration in the liquid. Consequently, low aluminium distribution coefficients are encountered when an aluminium-rich phosphate ore is used and vice versa. Finally, from mass balance calculations, the maximum allowable aluminium concentrations in the phosphate ores are predicted for hemi(dihydrate) phosphoric acid processes. Above these concentrations, unwanted calcium sulfate dihydrate DH formation can take place but this does not always occur.
Ma, Sanjian, Martynowicz, E.T.M.J., Witkamp, G.J., van Rosmalen, G.M.
Dissolution kinetics of phosphate ore in acidic solutions
(1994) Chinese Journal of Chemical Engineering, 2 (2), pp. 72-81.
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ABSTRACT: The dissolution kinetics of Florida and Jordan phosphate ore was studied in diluted nitric acid (0.2, 0.5, 1.0 mol · L-1), and in phosphoric acid (55 wt% H3PO4) aqueous solutions. It was found that the hydrogen ions concentration is a controlling factor, but the calcium ions concentration can not affect the dissolution rate in the range of 0.0 and 2.0 wt% Ca2+. The effects of temperature, stirring intensity and the size of ore particles were also investigated. The transfer of hydrogen ion depends on the diffusion, while the calcium ions transfer is assumed to be depended on mechanically stripping. The shrinking core model with hydrogen ions diffusion control match the experimental results.
de Vreugd, C.H., Witkamp, G.J., van Rosmalen, G.M.
Growth of gypsum III. Influence and incorporation of lanthanide and chromium ions
(1994) Journal of Crystal Growth, 144 (1-2), pp. 70-78.
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ABSTRACT: The growth of gypsum is retarded by lanthanide ions present in the solution as impurities. The crystal faces show macrostep formation. At relative supersaturations of 0.2 the growth retarding influence of the ions decreases in the order La3+ ≈ Ce3+ ≈ Eu3+ > Er3+ > Cr3+ > Cr2O2- 7, with a maximal difference of a factor 10 between the blank and La3+ at a concentration of 3 x 10-4M. At increasing supersaturations this difference becomes smaller and finally disappears at σ = 1. The uptake of lanthanides increases with increasing ionic radius, with a maximum for Ce3+. The sequences of growth retardation performance and uptake of the ions are therefore roughly similar. At higher supersaturations the uptake becomes higher. From the growth retardation as a function of the La3+ concentration an absorption energy of 30 kJ/mol was calculated. From adsorption experiments, no adsorption energy could be derived. The incorporation of Cd2+ ions in the presence of lanthanides behaves similarly as without these ions. © 1994.
Elgersma, F., Witkamp, G.J., Van Rosmalen, G.M.
Simultaneous dissolution of zinc ferrite and precipitation of ammonium jarosite
(1993) Hydrometallurgy, 34 (1), pp. 23-47.
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ABSTRACT: Zinc ferrite (ZnO·Fe2O3) was converted, in a single-step seeded batch process, into ammonium jarosite (NH4Fe3(SO4)2(OH)6) at 95°C and at a pH which was kept constant at either 1.7 or 1.95. The conversion consists of the dissolution of zinc ferrite, which could be described by a surface reaction controlled shrinking core model, and the simultaneous precipitation of ammonium jarosite, which is also a surface-reaction-controlled process. The supersaturation during conversion for the precipitation of jarosite was calculated from the solution composition. At pH 1.7 virtually 100% conversion of zinc ferrite is achieved. This leads to a residual zinc content of the solids produced of below 0.1 wt%. X-ray diffraction analyses of the product showed correspondingly small amounts of zinc ferrite. This indicates that the zinc incorporation in the jarosite lattice is practically negligible. The advantages of such a controlled conversion process for industrial practice are discussed. © 1993.
Elgersma, F., Witkamp, G.J., van Rosmalen, G.M.
Kinetics and mechanism of reductive dissolution of zinc ferrite in H2O and D2O
(1993) Hydrometallurgy, 33 (1-2), pp. 165-176.
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ABSTRACT: Synthetic zinc ferrite (ZnO·Fe2O3) samples were dissolved in 1 M HClO4 solutions with dissolved Fe(ClO4)2 at 90°C. The dissolution rate of ZnO·Fe2O3 was dependent upon the Fe2+ concentration, with an order of 0.43±0.03. It was shown that equivalent leach experiments carried out in D2O and H2O in the presence of 5 g/l Fe2+ resulted in a dissolution rate which was twice as high in H2O as in D2O. In 0.5 M H2SO4 at 90°C, in the absence of Fe2+ ions, the rate constant for ZnO·Fe2O3 dissolution was 11% higher in H2O than in D2O. A mechanism is proposed which describes the dissolution of ZnO·Fe2O3 in the presence and in the absence of complexing or reducing agents in H2O or D2O. © 1993.
van Put, J.W., Witkamp, G.J., van Rosmalen, G.M.
Formation of ammonium paratungstate tetra- and hexa-hydrate. I: stability
(1993) Hydrometallurgy, 34 (2), pp. 187-201.
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ABSTRACT: The crystallization of ammonium paratungstate tetrahydrate, ((NH4)10OH2W12O42·4H2O, APT·4H2O) from aqueous ammonium tungstate solutions is a key unit operation in current tungsten powder production. A literature survey showed that ammonium paratungstate hexahydrate (APT·6H2O) can form under conditions where APT·4H2O forms as well. Based on this information it was postulated that APT·6H2O is metastable. Experiments were carried out to determine whether and under what conditions the hexahydrate is metastable. It was found that the hexahydrate is metastable at a solution concentration of approximately 300-230 g/kg WO3 and from approximately 90° to 96°C. APT·6H2O is not formed when APT·4H2O seeds are added prior to crystallization. The experimental data are presented in a three-dimensional ternary phase diagram. It was found that the recrystallization of APT·6H2O into APT·4H2O is prompted by a decreasing water activity in solution during crystallization. The increase in solution temperature during isobaric crystallization also stimulates the recrystallization process. In industrial practice some residual crystals are always present in the crystallizer. Therefore, APT·6H2O will not form during industrial crystallization. © 1993.
Elgersma, F., Witkamp, G.J., van Rosmalen, G.M.
Incorporation of zinc in ferrous sulfate monohydrate
(1993) Hydrometallurgy, 33 (3), pp. 301-311.
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ABSTRACT: Continuous crystallization experiments on FeSO4 · H2O in aqueous solutions containing Zn2+ were carried out, at temperatures of 140-165°C, in a stainless steel/glass autoclave. The incorporation of Zn2+ in FeSO4 · H2O as a function of process parameters such as the temperature and the residence time was determined. Additionally, the solubility of FeSO4 · H2O in this temperature region in the presence of ZnSO4 was determined. The crystallization of FeSO4 · H2O yielded a product which contained between 2 and 3 wt% Zn2+, depending on the process conditions. The incorporation of Zn2+ was also quantified using a partition coefficient which, together with the calculated results for the supersaturation in the various experiments, revealed that the incorporation of Zn2+ in FeSO4 · H2O increased with the supersaturation, but was mainly influenced by the thermodynamic value of the partition coefficient; that is, a value equal to 0.3 at zero supersaturation. The separation of Fe2+ and Zn2+ from aqueous solutions by crystallization of FeSO4 · H2O has too low a selectivity to justify its use in an integrated hydrometallurgical jarosite treatment process. © 1993.
Elgersma, F., Witkamp, G.J., van Rosmalen, G.M.
Incorporation of zinc in continuous jarosite precipitation
(1993) Hydrometallurgy, 33 (3), pp. 313-339.
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ABSTRACT: Ammonium jarosite was precipitated in a 1.5 l continuous Mixed Suspension Mixed Product Removal crystallizer in the presence of varying feed Zn2+, Mg2+, Li+ and NH+ 4 concentrations. The feed Fe3+ concentration and SO2- 4 concentration were kept constant at 0.25 M and 1.6 M, respectively. The experiments were carried out at 95°C and pH 1.5, using residence times varying between 0.8 and 2.0 h. The following parameters were determined: steady state conversion, the jarosite crystal growth rate, the nucleation rate, the specific surface area, the solids density in the suspension, the production rate, the supersaturation and the incorporation of zinc or magnesium in the jarosite lattice. The residence time distribution of the system was determined by adding alunite as tracer. Additional experiments were carried out at a pH of 1.2 and 1.8 respectively, in order to determine the influence of the pH on the precipitation. Based on the results obtained the incorporation of zinc in jarosite or the jarosite production rate may be predicted for a wide range of process conditions. The incorporation of zinc in ammonium jarosite, probably via isomorphous substitution, is about 2-10 g/kg depending on the process conditions. This implies that in industrial practice the loss of zinc due to the removal of iron as jarosite ranges between 0.12 and 0.6 wt%, for a zinc concentrate containing 52 wt% zinc and 8 wt% iron. © 1993.
Elgersma, F., Kamst, G.F., Witkamp, G.J., Van Rosmalen, G.M.
Acidic dissolution of zinc ferrite
(1992).
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ABSTRACT: The dissolution of synthetic and industrial zinc ferrite was studied in nitric acid, perchloric acid and sulphuric acid solutions, at temperatures ranging from 75 degreesC to 95 degreesC and in the presence of an excess of Fe "SUP 2+" , Fe "SUP 3+" or Zn "SUP 2+" ions. The rate constant describing this dissolution process was obtained by using a surface-reaction controlled, shrinking core model, which yielded good results. A dissolution mechanism is proposed which qualitatively explains the results obtained. (from Authors)
Elgersma, F., Kamst, G.F., Witkamp, G.J., van Rosmalen, G.M.
Acidic dissolution of zinc ferrite
(1992) Hydrometallurgy, 29 (1-3), pp. 173-189.
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ABSTRACT: The dissolution of synthetic and industrial zinc ferrite was studied in HNO3, HClO4 and H2SO4 solutions, at temperatures ranging from 75°C to 95°C and in the presence of an excess of Fe2+, Fe3+ or Zn2+ ions. The rate constant describing this dissolution process was obtained by using a surface-reaction controlled, shrinking core model, which yielded good results. The dissolution rate zinc ferrite depends on the square root of the hydrogen ion activity in H2SO4 and HClO4 solutions. The apparent activation energy for the dissolution equals 74±2 kJ/mol in H2SO4, 47±22 kJ/mol in HClO4 and 37±16 kJ/mol in HNO3. The order of the rate constant was 0.6 in the Fe2+ and -0.5 in the Fe3+ concentration. The rate constant for the dissolution of industrial zinc ferrite was 20-50% lower than for synthetic zinc ferrite. The presence of 85 g/l Zn2+ in the leach solution retarded the dissolution rate of zinc ferrite. A dissolution mechanism is proposed which qualitatively explains the results obtained. © 1992.
Witkamp, G.J., van Rosmalen, G.M.
Growth of gypsum II. Incorporation of cadmium
(1991) Journal of Crystal Growth, 108 (1-2), pp. 89-98.
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ABSTRACT: The cadmium uptake in gypsum has been investigated using the techniques of constant composition, simple precipitation and continuous crystallization. The partition coefficient D increases from (4-8)×10-3 at low supersaturations σ to 5x10-3 at a σ equal to 1.5. D is slightly higher in solutions with a higher electrolyte (NaNO3) concentration, partly due to a higher activity coefficient of Cd2+. A higher temperature also results in a higher uptake. From adsorption experiments it follows that the affinity of Cd2+ to SO2- 4 at the crystal surface is not larger than for Cd2+ to SO2- 4 in the solution. © 1991.
Witkamp, G.J., Van der Eerden, J.P., Van Rosmalen, G.M.
Growth of gypsum. I. Kinetics
(1990) Journal of Crystal Growth, 102 (1-2), pp. 281-289.
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ABSTRACT: A suspension of gypsum (CaSO4{down triangle, open}2H2O) crystals has been grown from electrolyte solutions using the constant composition technique. In pure water a parabolic rate law governs the growth kinetics, while in NaNO3 solutions the order increases from 1 at low supersaturations up to 4 at higher supersaturations. In NaNO3 platelike crystals with some roughened faces develop under the given growth conditions. The higher growth rate in electrolyte solutions is partly due to the higher impingement rate and partly to a higher incorporation rate at the surface. The growth rate increases with increasing temperature. © 1990.
Witkamp, G.J., Seckler, M.M., Bruinsma, O.S.L., Van Rosmalen, G.M.
Recrystallization of calcium sulfate in phosphoric acid solutions; batchwise operation
(1990) Journal of Crystal Growth, 99 (1 -4 pt 2), pp. 1117-1123.
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ABSTRACT: A model is presented for the solvent mediated batchwise recrystallization of hemihydrate into dihydrate. The model takes into account the rates of dissolution of hemihydrate and of growth of gypsum. These rates result from the driving forces (under- and supersaturation) that are influenced by temperature and acid concentrations, and from the rate constants, which are mainly affected by impurities. Secondary nucleation can be neglected with respect to the observed recrystallization rates. The presented model can also be applied more generally.
van der Leeden, Mieke C., van Rosmalen, Gerda M., de Vreugd, Kees, Witkamp, Geertjan
Influence of additives and contaminents on crystallization processes [Einfluss von Additiven und Verunreinigungen auf Kristallisationsprozesse]
(1989) Chemie-Ingenieur-Technik, 61 (5), pp. 385-395.
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ABSTRACT: The presence of additives and contaminants in a crystallising solution can have a considerable influence on the crystallisation properties of the products, such as nucleation and growth kinetics, agglomeration or dispersion of the crystals, and the incorporation of foreign ions into the crystal lattice. These influences are caused by various mechanisms, depending upon the type of additive or contaminant. Tailor-made and multifunctional additives are distinguished. Trace amounts of metal ions can also modify the kinetics of crystallisation. The metal ions can be incorporated to a greater or lesser extent in the crystal, depending upon thermodynamic and kinetic factors.
Van Der Voort, D., Blasse, G., Witkamp, G.J., Van Rosmalen, G.M., Brixner, L.H.
The luminescent Eu3+ ion as a probe of lanthanide impurities in crystallized gypsum
(1989) Materials Chemistry and Physics, 24 (1-2), pp. 175-187.
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ABSTRACT: The luminescence of the Eu3+ ion in gypsum, CaSO4·2H2O, crystallized from aqueous solutions, is investigated in order to contribute to the unravelling of the precipitation mechanism of gypsum in industrial processes where all kinds of impurities are distributed between the solution and the crystals. Na+-containing solutions show NaEu(S04)2·H2O crystallization next to Eu3+ incorporated into the gypsum lattice. The Eu3+ ion in gypsum shows extraordinary luminescence characteristics, caused by a strong linear crystal-field. The quantum efficiency of the luminescence is low due to the strong relaxation in the excited charge-transfer state and the quenching by the water molecules coordinating the Eu3+ ion in the gypsum lattice. The Eu3+ ion can be used as a probe to investigate lanthanide impurities in crystallized gypsum. © 1989.
Van Der Sluis, S., Witkamp, G.J., Van Rosmalen, G.M.
Crystallization of calcium sulfate in concentrated phosphoric acid
(1986) Journal of Crystal Growth, 79 (1-3 PART 2), pp. 620-629.
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ABSTRACT: In a continuous crystallization procedure calcium sulfate hemihydrate (HH) crystals were formed by feeding a calcium dihydrogen phosphate (CDHP) solution in concentrated phosphoric acid (5.6 and 6.6 mol H3PO4 per kg), simultaneously with a sulfuric acid solution, into a 1 litre crystallizer at 92°C. The slurry removal occurred unclassified. Residence times of 20 to 80 min were maintained. The solid over liquid weight ratio depended on the calcium content of the CDHP solution. By slight adjustment of the feed streams the molar calcium over sulfate ratio in the solution was varied between about 0.05 and 8. A cadmium concentration of 30 ppm was maintained in the crystallizing solution. The shape of the HH crystals varied with increasing sulfate concentrations from mainly aggregates to mainly needles. During crystallization of the HH crystals, cadmium as well as phosphate ions are incorporated into the lattice. The degree of uptake strongly depends on the operating conditions. The phosphate uptake decreases with increasing sulfate concentrations in the crystallizer, while the cadmium uptake increases. The molar phosphate over sulfate ratio in the crystals is found to be proportional to the same ratio in the solution. A comparable linear relationship is also observed for the molar cadmium over calcium ratios at a residence time of 20 min. At high sulfate concentrations, long residence times and high temperatures (about 92°C), the stable anhydrite modification (AH) tends to develop next to the metastable HH phase. The cadmium uptake in AH is at least 10 times higher than in HH, while the phosphate uptake is not influenced by a small amount of AH in the crystals. The cadmium incorporation in the HH lattice can be reduced by adding halogenides to the solution. © 1986.
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