| 1. |
- Alander, E. M., et al.
(författare)
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Characterization of paracetamol agglomerates by image analysis and strength measurement
- 2003
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 130:1-3, s. 298-306
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Tidskriftsartikel (refereegranskat)abstract
- Paracetamol is crystallized in different solvents and techniques are developed and used to characterize the product. The product particles from three different solvent compositions: ethylene glycol, acetone and an acetone-water mixture (30-70 wt.%) have been examined. Product properties visually observed are quantified by image analysis and evaluation of measured image descriptors with Principal Component Analysis (PCA). The agglomerate strength has been determined by crushing single agglomerates. Depending on the solvent, the content of single crystals and agglomerates differ. Agglomerates differ by the number and size of crystals grown together, as well as by the strength.
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| 2. |
- Gracin, Sandra, et al.
(författare)
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Polymorphism and Crystallization of p-Aminobenzoic Acid
- 2004
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 4:5, s. 1013-1023
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Tidskriftsartikel (refereegranskat)abstract
- p-Aminobenzoic acid (PABA) crystallizes in two different polymorphic forms: the alpha-polymorph, which is the commercially available form and appears as long, fibrous needles, and the beta-polymorph, which appears in the form of prisms. The thermodynamic stability and crystallization from different solvents have been studied experimentally. The system is found to be enantiotropic with a transition temperature of 25degreesC, below which the beta-form is the stable polymorph. The compound has been crystallized from 13 different solvents, either by slow cooling after which the product is allowed to mature in suspension, or by rapid cooling followed by immediate isolation. Needles were obtained from all solvents by both methods. In water and in ethyl acetate, at slow cooling below 20degreesC, the prismatic beta-form is obtained, however, often together with the needles. The beta-form crystals usually needed hours or days to grow at the very slow cooling used, while needles usually appeared in seconds. By careful control of supersaturation and temperature, cooling crystallization can be performed to produce the pure beta-form in water and in ethyl acetate. The influence of the solvent is explained by analysis of the crystal structures versus the possible interaction of the solvent molecules with the solute in solution. The alpha-form structure is governed by carboxylic acid dimers and is kinetically favored since it is believed that the corresponding dimers easily form in the solution, especially in less polar solvents.
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| 3. |
- Gracin, Sandra, et al.
(författare)
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Prediction of Solubility of Solid Organic Compounds in Solvents by UNIFAC
- 2002
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 41:20, s. 5114-5124
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Tidskriftsartikel (refereegranskat)abstract
- Predictions of solubility of nine different solid organic fine chemical compounds in water and organic solvents of relevance to industrial processing are examined. UNIFAC interaction parameters are taken from standard reference literature, extracted from liquid-vapor equilibria. For most systems, predicted solubilities deviate more than 15% from experimental values. Deviations are due to uncertainties in the estimation of the activity of the pure solid as well as to deficiencies in the estimation of activity coefficients in the solution. By comparison with results from ab initio quantum chemical calculations of the elecrostatic potential on the molecular surface of the solutes, it can be shown that a key assumption of the UNIFAC approach is not necessarily fulfilled. The properties of a functional group may depend significantly on the properties of the rest of the molecule.
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| 4. |
- Gracin, Sandra, et al.
(författare)
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Solubility of Phenylacetic Acid, p-Hydroxyphenylacetic Acid, p-Aminophenylacetic Acid, p-Hydroxybenzoic Acid, and Ibuprofen in Pure Solvents
- 2002
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Ingår i: Journal of Chemical and Engineering Data. - : American Chemical Society (ACS). - 0021-9568 .- 1520-5134. ; 47:6, s. 1379-1383
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Tidskriftsartikel (refereegranskat)abstract
- The solubility of phenyl acetic acid, p-hydroxyphenylacetic acid, p-aminophenylacetic acid, p-hydroxybenzoic acid, and ibuprofen in water and in a range of organic solvents of relevance to industrial processing is reported. The solvents used are water, methanol, ethanol, 2-propanol, acetone, 4-methyl-2-pentanone, ethyl acetate, chloroform, and toluene. Solubility data are discussed from the standpoint of molecular aspects of solute-solvent interactions and by estimated solid-phase activity.
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| 5. |
- Granberg, R. A., et al.
(författare)
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Primary nucleation of paracetamol in acetone-water mixtures
- 2001
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 56:7, s. 2305-2313
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Tidskriftsartikel (refereegranskat)abstract
- The influence of solvent composition on primary nucleation of 4-hydroxyacetanilide (paracetamol) in acetone-water mixtures is investigated. The induction time for primary nucleation is determined, at various degrees of supersaturation and at different temperatures, in different solvent mixture compositions. Supersaturation is generated by the addition of water. and the homogeneous, agitated, isothermal solution is allowed to nucleate. The supersaturation driving force is calculated as the difference in the chemical potential. At equal thermodynamic driving force, the induction time depends on the composition of the solvent mixture. The interfacial energy is in the range 1-3 mJ/m(2) and tends to increase with decreasing solubility, i.e. increasing water content. The interfacial energy is slightly lower than a value calculated from a contact angle measurement (5 mJ/m(2)) in pure water and is significantly lower than values predicted by equations derived From simplified theories.
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| 6. |
- Granberg, R. A., et al.
(författare)
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Solubility of paracetamol in binary and ternary mixtures of water + acetone + toluene
- 2000
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Ingår i: Journal of Chemical and Engineering Data. - : American Chemical Society (ACS). - 0021-9568 .- 1520-5134. ; 45:3, s. 478-483
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Tidskriftsartikel (refereegranskat)abstract
- The solubility of paracetamol (4-hydroxyacetanilide) in binary mixtures of acetone + water and acetone + toluene and in ternary mixtures of water + acetone + toluene is reported. The temperature range is -5 to +30°C. In acetone + water the solubility increases to a maximum at approximately 25 mass % water before decreasing to a much lower value in pure water as compared to pure acetone. In acetone + toluene the solubility decreases monotonically with increasing toluene concentration. The water content has a strong influence also in ternary mixtures. Activity coefficients in the saturated solutions are estimated.
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| 7. |
- Lindberg, M., et al.
(författare)
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Reaction crystallization in strained fluid films
- 2001
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 56:10, s. 3257-3273
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Tidskriftsartikel (refereegranskat)abstract
- The detailed conditions during the ultimate stage of micromixing of the reactants in a reaction crystallization process are analysed. A mathematical model is developed to describe mass transfer, chemical reaction, and crystallization of a molecular compound in strained lamellar structures of reactant solutions inside the smallest vortices. The numerical calculations show that the supersaturation varies significantly in space and time, and suggest that significant crystallization may occur inside these vortices in the case of low-soluble and sparingly soluble compounds. At the end of the vortex lifetime, the crystal size distribution is quite dependent on the properties of the system and on the processing conditions. The number of crystals generated correlates strongly to the maximum supersaturation occurring during the vortex lifetime, and this maximum supersaturation is as a first approximation well described by simplified mass transfer models where crystallization is neglected. Often a significant supersaturation remains at the end of the vortex lifetime and the size of the crystals leaving the vortex is determined by the growth rate rather than by nucleation and mass constraint. The mean size is usually larger than the limiting size for Ostvald ripening in the bulk and the size distribution is quite narrow. The results show that neglect of the detailed conditions in reaction crystallization of a molecular compound may not be justified.
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| 8. |
- Lindberg, M., et al.
(författare)
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Supersaturation generation at the feed point in reaction crystallization of a molecular compound
- 2000
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Ingår i: Chemical Engineering Science. - 0009-2509 .- 1873-4405. ; 55:10, s. 1735-1746
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Tidskriftsartikel (refereegranskat)abstract
- The maximum product concentration of a molecular compound at the feed point in reaction crystallization is analysed by modelling. A model describing unsteady mass transfer and chemical reaction in strained, semi-infinite, fluid films is combined with models describing productivity constraints and reactant concentration changes during the course of a process. The maximum product concentration is taken as a first estimate of the maximum supersaturation and is used as a basis to discuss the product crystal size that may be produced. The result suggests that at certain conditions we may find smaller product crystals at decreased reactant concentrations. The maximum concentration varies during the course of a single-feed semibatch process and the highest value is not necessarily found in the beginning. The variation with time, depends on the choice of the reactant to feed, and the results provide an explanation to why the product crystal mean size may depend on the choice of feed reactant. Guidelines are proposed for how to decide on optimum reactant solution concentrations and for how to select the reactant to feed in a semibatch process. In addition it is suggested that larger crystals may be produced if the feed reactant concentration is low early in the process and is allowed to gradually increase with time in a controlled way. The term programmed feed concentration'' is introduced.
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| 9. |
- Nordström, Fredrik, et al.
(författare)
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Analysis of solution nonideality of a pseudomorphic drug system through a comprehensive thermodynamic framework for the design of a crystallization process
- 2004
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 93:4, s. 995-1004
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Tidskriftsartikel (refereegranskat)abstract
- Solutions of a semipolar drug belonging to the alpha(v) beta(iii) integrin antagonist class of compounds were studied in a comprehensive thermodynamic framework. The solubility of two pseudomorphic forms (an anhydrate and a monohydrate) was measured at several temperatures and various solvent mixtures of acetonitrile and water. Both forms displayed a bell-shaped solubility behavior as a function of cosolvent composition. Thermodynamic framework used to analyze the data comprised van't Hoff and enthalpy-entropy compensation analyses. The two pseudomorphs exhibited linear temperature dependence from 25 to 65degreesC at all solvent compositions (i.e., ideal behavior with temperature for fixed solvent composition). Plots of enthalpy of solublization and Gibbs free energy showed two distinct regions with contrasting thermodynamic, and consequently, underlying structural properties (indicating non-deal behavior with solvent composition for a fixed temperature). Solubility increased due to entropy effects in the acetonitrile rich region, whereas enthalpy effects dominated solublization in the water-rich region. Quantification of this phenomenon by plotting DeltaH versus DeltaG showed considerable nonlinearity, and that the two regions were separated by a significant discontinuity-a trend rarely seen before in the literature. The reason behind this behavior is believed to be due to the complex interactions in the solution of the drug in water acetonitrile solvent system. A very significant aspect of the comprehensive thermodynamic analysis is that it helped explain the puzzling feature of the data, which showed that the free energy of phase transformation between the two pseudomorphic forms for a given temperature was not independent of the solvent composition. The resulting explanation has major consequences for crystallization process development.
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| 10. |
- Pino-Garcia, Osvaldo, et al.
(författare)
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Influence of additives on nucleation of vanillin : Experiments and introductory molecular simulations
- 2004
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 4:5, s. 1025-1037
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Tidskriftsartikel (refereegranskat)abstract
- Nucleation of vanillin (VAN) in 2-propanol/water in the presence of additives, viz., acetovanillone (AVA), ethyl vanillin (EVA), guaiacol (GUA), guaethol (GUE), 4-hydroxyacetophenone (HAP), 4-hydroxybenzaldehyde (HBA), and vanillic acid (VAC) is investigated experimentally and by molecular simulations. In the experimental work, the induction time for nucleation is measured at different temperatures and levels of supersaturation using a multicell apparatus. A large variation in the experimental data is observed, and this variation is analyzed by statistical methods. By classical nucleation theory, the induction time data are used to estimate the solid-liquid interfacial energy of vanillin for each VAN-additive system. At 1 mol %, the interfacial energy becomes lower in the presence of AVA, EVA, HAP, and VAC, while it becomes higher in the presence of the other additives. As the additive concentration increases from 1 to 10 mol %, the interfacial energy also increases. The interfacial energy ranges from 6.9 to 10.1 mK m(-2). Molecular modeling, implemented in the program Cerius2, is used to simulate and examine the surface chemistry of the likely crystal growth faces of VAN (i.e., {001} and {100}). To evaluate the additive-crystal face interaction energy, two approaches are used: the surface adsorption method and the lattice integration method. Both experimental and molecular simulation results indicate that the additives studied are potential modifiers of the nucleation of VAN. However, a simple and clear relationship between the experimental values of interfacial energy and the calculated interaction energies for the most important crystal faces of VAN cannot be identified. The modeling does not concern the actual nucleation but rather the conditions of a growing surface and are based on several severe simplifications. Obviously, this simplistic approach does not sufficiently capture the influence of additives on the nucleation of vanillin.
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| 11. |
- Pino-Garcia, O., et al.
(författare)
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Primary nucleation of vanillin explored by a novel multicell device
- 2003
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 42:20, s. 4899-4909
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Tidskriftsartikel (refereegranskat)abstract
- A novel multicell apparatus is designed, constructed, and used to investigate crystal nucleation of vanillin in water/2-propanol solution (20 mass % of 2-propanol on a solute-free basis). The device contains 15 nucleation cells, with volumes of about 6 cm(3) each, in which the induction times for nucleation are measured simultaneously. The nucleation in the cells is continuously video-recorded and analyzed offline. The induction time for nucleation of vanillin is determined at various levels of supersaturation and temperature, and by classical nucleation theory the solid-liquid interfacial energy is estimated to 7.3 +/- 0.2 mJ m(-2). A large variation in the experimental data is observed, and this variation is analyzed by statistical methods.
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| 12. |
- Profir, Veronica M., et al.
(författare)
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Influence of solvent and the operating conditions on the crystallization of racemic mandelic acid
- 2004
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 4:2, s. 315-323
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Tidskriftsartikel (refereegranskat)abstract
- The crystallization of racemic mandelic acid is studied in unseeded batch cooling experiments in four solvent systems. Apart from the thermodynamically stable racemic compound, a metastable modification of the racemic compound is also found to initially form upon nucleation. The metastable racemate is characterized by thermal analysis (MDSC), FTIR spectroscopy, and X-ray powder diffraction (XRPD). The experiments show that the type of crystal modification that is formed upon nucleation is strongly influenced by the operating conditions such as filtration, cooling rate, and stirring rate, as well as by the solvent. The solvent effect can be related to the characteristics of the crystal structures of the two modifications, and to the hydrogen bonding properties of the solvent. The crystal structure of the metastable modification of the racemic compound is very similar to that of the pure enantiomer, which explains the similarity of the FTIR spectra, the XRPD diffraction pattern, and the thermodynamic stability.
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| 13. |
- Profir, V. M., et al.
(författare)
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Study of the crystallization of mandelic acid in water using in situ ATR-IR spectroscopy
- 2002
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 2:4, s. 273-279
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Tidskriftsartikel (refereegranskat)abstract
- Different aspects related to the separation of enantiomers of mandelic acid by direct crystallization are explored. Solubility, nucleation, and solid-phase transformation in aqueous solutions are investigated. Results show that a metastable conglomerate can be formed for a substance known to appear as a racemic compound. After a time-lag, the conglomerate transforms into the stable racemic compound. The time-lag ranges from a few minutes to 8 h depending on the operation conditions. The time-lag decrease's at increasing concentration/temperature and in the presence of micrometer-sized particles. In situ attenuated total reflectance infrared (ATR-IR) spectroscopy and a partial least squares (PLS) calibration model are used to record the concentration of dissolved mandelic acid. Since no sampling is required and the calibration set, which is used on both racemic and enantiomerically pure solutions, can be built using the cheaper racemate, the technique should be of particular interest in applications involving chiral substances.
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| 14. |
- Ståhl, Marie, et al.
(författare)
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Aging of reaction-crystallized benzoic acid
- 2004
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Ingår i: Industrial and engineering chemistry research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 43, s. 6694-6702
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Tidskriftsartikel (refereegranskat)abstract
- Benzoic acid has been crystallized by mixing sodium benzoate and hydrochloric acid in a T-mixer. The suspension is collected in an agitated crystallizer, and aging of the solid product is evaluated by microscopy. In addition, the kinetics of aging is examined by population balance modeling and nonlinear parameter estimation. Microscopic observations reveal that the crystal shape is quite irregular immediately after the T-mixer crystallizer, but during the aging the crystals turn into nice well-shaped platelets. A model on Ostwald-type ripening gives a fairly good description of the evolution of the crystal size distribution during the aging, provided that the observed changes in crystal shape are accounted for in the model.
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| 15. |
- Ståhl, Marie, et al.
(författare)
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Reaction crystallization kinetics of benzoic acid
- 2001
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 47:7, s. 1544-1560
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Tidskriftsartikel (refereegranskat)abstract
- Benzoic acid was crystallized in a T-mixer by mixing hydrochloric acid and an aqueous sodium benzoate solution. Crystallization kinetics were determined by population balance modeling and parameter estimation by nonlinear optimization. The evaluation of several models showed that the model has to be carefully designed. The objective function is highly nonconvex, and the results have to be scrutinized to identify the appropriate optimum. Growth-rate dispersion needs to be accounted for to obtain a reasonable description of experimental product-size distributions. Six parameters of nucleation and growth kinetics were determined simultaneously in an optimization that includes experimental product-size distributions from 14 experiments at 8 different initial supersaturations. The interfacial energy calculated from the corresponding nucleation parameter is 0.015 J/m2. The exponent of the normal power law growth-rate equation receives a value of 2.1, suggesting that growth is controlled by surface integration. The value becomes 2.9 if the logarithm of the supersaturation ratio is used as the driving force. The coefficient of variation of the growth-rate distribution depends only weakly on supersaturation and receives a value of 0.23 if this dependence is neglected. The final model describes experimental data well. The estimated parameters are physically reasonable and provide a physically reasonable description of the entire experiment.
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| 16. |
- Torbacke, Marika, et al.
(författare)
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Influence of different scales of mixing in reaction crystallization
- 2001
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Ingår i: Chemical Engineering Science. - : Elsevier. - 0009-2509 .- 1873-4405. ; 56:7, s. 2459-2473
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Tidskriftsartikel (refereegranskat)abstract
- Experiments on semibatch reaction crystallization of benzoic acid are reported. The conditions in an agitated tank are simulated by a loop reactor by which feed point mixing conditions can be controlled separately from the macroscale circulation rate. Hydrochloric acid is fed into a circulating solution of sodiumbenzoate and the in#uence of macromixing, mesomixing and micromixing on the product crystal mean size is evaluated. The product mean size increases with increasing circulation rate in the loop, with increasing feed point mixing intensity, with decreasing feed rate and with decreasing feed pipe diameter. Increased mixing intensity on any level leads to larger product crystals, but especially the rate of mesomixing is of importance. The in#uence of the feed pipe diameter is opposite to predictions by available theories and cannot be explained by backmixing into the feeding pipe. All results can be correlated quite well against a dimensionless mixing e$ciency de"ned as the ratio of the reactant feeding time to the mixing time. The mixing time is the sum of the time constants for mesomixing and micromixing. A new mesomixing time constant is de"ned as being proportional to the ratio of the feed pipe diameter and the velocity of the bulk #ow passing the feed pipe.
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| 17. |
- Torbacke, Marika, et al.
(författare)
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Mesomixing in semi-batch reaction crystallization and influence of reactor size
- 2004
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 50:12, s. 3107-3119
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Tidskriftsartikel (refereegranskat)abstract
- Experiments on semibatch reaction crystallization of benzoic acid are reported, in which hydrochloric acid was fed into an agitated solution of sodium benzoate. The influence of mixing and the influence of reactor size are examined on the product crystal mean size. The product mean size increases with increasing stirring rate and with decreasing feed rate. At low feed rates, the mean size increases at decreasing feed pipe diameter. At high feed rates the influence of the feed pipe diameter is more complex. Micromixing is of some importance in most experiments, but the rate of mesomixing especially governs the process. Mesomixing seems to be adequately described by the inertial-convective disintegration mechanism. In many aspects experimental results cannot be described by the turbulent-dispersion mechanism. The product mean size does not exhibit a clear dependence on reactor size, but depends more strongly on other parameters. Results from experiments from 1 L scale to 200 L scale can be correlated fairly well against a dimensionless number defined as the ratio of the total time of reactant feeding to the time constant of mixing. The best representation of the mixing time constant is obtained by making it directly proportional to the ratio of the feed pipe diameter and the linear velocity of the bulk flow passing the feed pipe. The proportionality constant can be calculated from turbulence data. over the bulk flow at the feed point.
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| 18. |
- Uus-Penttila, M. S., et al.
(författare)
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Experimental study for agglomeration behaviour of paracetamol in acetone-toluene-water systems
- 2003
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Ingår i: Chemical engineering research & design. - 0263-8762 .- 1744-3563. ; 81:A4, s. 489-495
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Tidskriftsartikel (refereegranskat)abstract
- Agglomeration behaviour of paracetamol was studied in acetone-toluene-water systems. The aim was to experimentally determine how the solvent composition influences the agglomeration tendency of paracetamol. It was found that for the chosen solvent system there is one main region where paracetamol agglomerates: the region with large amounts of acetone (>65 wt%) and very small amounts of water (<4 wt%). The same behaviour can be observed both within the one-phase region and within the two-phase region. The experimental agglomeration results were compared with molecular simulations from literature. Both methods indicate that it is more likely for paracetamol crystals to agglomerate in organic systems than in aqueous systems.
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| 19. |
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| 20. |
- Vendel, M., et al.
(författare)
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Initiation of incrustation by crystal collision
- 2000
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Ingår i: Chemical engineering research & design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 78:A5, s. 749-755
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Tidskriftsartikel (refereegranskat)abstract
- Initiation of incrustation by collision between crystals and a solid surface is investigated. The suspension flow towards the vessel wall in a crystallizer is simulated by laboratory experiments. A liquid jet of supersaturated suspension impinges on a plate at well defined hydrodynamics, supersaturation and parent crystal size. Experiments have been carried out with succinic acid/water. The results indicate that crusts may be initiated at supersaturation well below the metastable limit. Crusts are initiated on both Teflon(TM) and steel. More crust nuclei are formed by collision initiation on sanded stainless steel than on polished stainless steel or Teflon(TM). The results support the hypothesis that collision initiation of crusts is of industrial importance, and suggest that attention should be devoted to the hydrodynamics of crystallizers.
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| 21. |
- Westin, K. J., et al.
(författare)
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Precipitation of calcium carbonate in the presence of citrate and EDTA
- 2003
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Ingår i: Desalination. - 0011-9164 .- 1873-4464. ; 159:2, s. 107-118
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Tidskriftsartikel (refereegranskat)abstract
- The influence of process conditions such as feed rate, calcium/carbonate ratio, pH, complexing agents [ethylenediaminetetraacetic acid (EDTA), citrate (CIT)] and their concentration on the average particle size and shape of precipitated calcium carbonate was studied. The precipitation was performed in a semi-batch operated agitated vessel at constant pH by adding sodium hydrogen carbonate to a solution containing calcium chloride. In the absence of a complexing agent, agglomerates of needle-shaped crystals, probably aragonite, are obtained. Increasing feed time and the calcium/carbonate ratio increases the average particle size, whereas the opposite effect is observed for increasing pH. The observations can be related to the level of supersaturation. In the presence of complexing agents and at a concentration ratio of calcium vs. a complexing agent of 6, differently shaped and smaller particles were obtained. Furthermore, the effect of the other parameters on particle size becomes much weaker in the presence of complexing agents. In the presence of EDTA mostly spherical particles were obtained, and in the presence of citrate mainly rhombic particles corresponding to calcite were obtained. The effect on particle shape and size is attributed to interactions of the complexing agents with the faces of the crystalline calcium carbonate.
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| 22. |
- Yu, Ziyun, et al.
(författare)
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Turbulence characteristics around the agitator in a dilute suspension
- 2001
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Ingår i: Journal of chemical engineering of Japan. - : Society of Chemical Engineers, Japan. - 0021-9592 .- 1881-1299. ; 34:5, s. 654-661
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Tidskriftsartikel (refereegranskat)abstract
- The turbulent field in a dilute suspension of solid particles, agitated by a pitched-blade turbine pumping downwards in an agitated tank, is investigated experimentally. A three-dimensional phase Doppler anemometer is used to measure local, instantaneous, three-dimensional velocities of the fluid and of the suspended particles. A shaft encoding technique is used to resolve the turbulent fluctuations from the periodic velocity fluctuation due to the impeller blades, and to provide a more detailed information about the variations in flow and particle concentration. The solid particles diverge from the flow especially below the agitator close to the tip where the strongest turbulence is found. Periodic fluctuations in the particle concentration relate to the variations found in the mean velocity and in the fluctuating velocity.
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| 23. |
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| 24. |
- Ålander, Eva M., et al.
(författare)
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Agglomeration of paracetamol during crystallization in pure and mixed solvents
- 2004
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 43:2, s. 629-637
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Tidskriftsartikel (refereegranskat)abstract
- The agglomeration of paracetamol during crystallization has been investigated. It is shown that the agglomeration behavior depends on the solvent composition. The following solvent systems were used in isothermal desupersaturation experiments: five different acetone-toluene-water mixtures and the pure solvents acetone, 2-propanol, acetic acid, and ethylene glycol. Sieving, image analysis processed by principal component analysis, and agglomerate strength measurements were used to characterize the product particles. Mixtures with a high concentration of acetone were found to produce a highly agglomerated product with strong agglomerates. In contrast, products from crystallization in ethylene glycol, 2-propanol, acetic acid, and acetone-toluene-water mixtures having a high concentration of water contained not only agglomerates but also a significant fraction of single crystals. Furthermore, the agglomerates formed in these solvents were much weaker than those produced in mixtures with a high content of acetone. The results were correlated with the polarity and the viscosity of the solvents.
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