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International audience; Nucleation, the birth of a stable cluster from disorder, is inherently stochastic. Yet up to date, there are no quantitative studies on NaCl nucleation that accounts for its stochastic nature. Here, we report the first stochastic treatment of NaCl-water nucleation kinetics. Using a recently developed microfluidic system and evaporation model, our measured interfacial energies extracted from a modified Poisson distribution of nucleation time show an excellent agreement with theoretical predictions. Furthermore, analysis of nucleation parameters in 0.5 pL, 1.5pL and 5.5 pL microdroplets reveals an interesting interplay between kinetic confinement and shifting of nucleation mechanisms. Overall, our findings highlight the need to treat nucleation stochastically rather deterministically to bridge the gap between theory and experiment.

Temperature cycling induced deracemization (TCID) is an attractive method to provide a pure enantiomer from a racemic solid phase. In this work, we performed deracemization of the nonessential amin...

Chirality plays an important role in the pharmaceutical industry since the two enantiomers of a drug molecule usually display significantly different bioactivities, and hence, most products are produced as pure enantiomers. However, many drug precursors are synthesized as racemates, and hence, enantioseparation has become a significant process in the industry. Cocrystallization is one of the attractive crystallization approaches to obtain the desired enantiomer from racemic compounds. In this work, we propose a chiral resolution route for an antiepileptic drug

The problem of separation and purification of the enantiomers of chiral species is a significant issue in the production of modern chemicals of pharmaceutical, agricultural and food industries. Efficient methods enabling a complete conversion of a racemic mixture into the desired enantiomer would be of great benefit to industry. Temperature cycle induced deracemization (TCID), a process allowing an initially racemic crystal phase of a suspension to be converted into an enantiopure state, combines solution phase racemization of the solute molecules and a series of temperature cycles inducing dissolution and crystal growth. The process first described as a more convenient and scalable alternative to Viedma ripening, has now been successfully tested on a wide range of chiral components that are conglomerate forming and racemizable. This review discusses the origins of TCID, potential mechanisms responsible for the deracemization, and also some related processes.

The conventional all-in/all-out batch management that is applied in most small to medium swine farms often provides an inconsistent feed of wastewater to biogas systems, causing an imbalance between the power requirements and generation capacity of a farm. This study proposes two alternative models that can be employed to ease this problem. In Model 1, the operation was divided into two offset batch intervals, while in Model 2, the operation used four separate offset batch intervals. The models developed here help avoid an unnecessary long lag phase in the digester, allowing more stable anaerobic digestion performance and more evenly distributed biogas production. Accordingly, the models produce a more stable supply of energy for domestic use, achieving a 36–44% reduction in the electricity expense or a savings of 43,782 m3 biogas/year or 35,834 kWh equivalent compared with that of conventional management. Conventional farm management has periods of excess and deficient biogas production; excess biogas is produced at a rate of up to 14,714 m3/year or 12,043 kWh equivalent at the peak period. This excess could be reduced by 79–100% by using the proposed farming models. This reduction is equivalent to greenhouse gas reductions of 9441 and 11,902 m3 CO2 eq./year by Models 1 and 2, respectively. Finally, a sensitivity analysis is used to show how the profitability of biogas plants would vary due to changes in some key parameters, such as the electricity buyback price. The results suggest that more profit could be attained from a significant reduction in operating costs by proper farm management without requiring additional investment.

This study is the first, to the best of our knowledge, where waste napkin paper was successfully valorized to low-density (27.2 mg cm−3) cellulose aerogels for oil sorption material. Two simple methods with different gel coagulators, ethanol and sulfuric acid, were used for preparation of the aerogel. Conditions for the alkaline treatment of the raw material and the pre-freezing temperature in the lyophilization process were optimized. It was found that the water and oil sorption capacities of the aerogels were not significantly affected by alkaline treatment, while they could be adjusted by changing the pre-freezing temperature. Although the produced aerogels were initially amphiphilic, hydrophobic surfaces were obtained by vapor deposition of methyltrimethoxysilane (MTMS) and these materials possessed high sorption capacities, up to 32.24 cm3 g−1 (28.56 g g−1) for pump oil and 26.77 cm3 g−1 (39.59 g g−1) for chloroform. This was comparable to aerogels prepared from fresh cellulosic materials via the sol-gel method, as their sorption capacities varied in the range of 14–45 g g−1.

The stereoisomeric system of rac-2-phenylglycinamide (PGA) and rac-N-acetyl tryptophan (NAT) is significant in the application of chiral resolution because it has been shown that this system can be used for enantioseparation of PGA and/or NAT using a novel deracemization route of the conglomerate salt formed. However, it was also found that the conglomerate salt eventually converted into different crystal forms that limited the time available for the separation. Herein, we try to understand the phase conversion occurring in this system using DSC, PXRD, and SC-XRD. The related structures of the salt (two polymorphs of the more stable homochiral (dd- and ll-) salts and one polymorph of the less stable heterochiral (dl- and ld-) monohydrate salts) are demonstrated and discussed relating to their relative stabilities. The successful deracemization was demonstrated using the heterochiral (dl- or ld-) monohydrate salts. However, following Ostwald’s rule of stages, only limited time is available for the deracemization before the metastable compound converts into the more stable homochiral (dd- and ll-) pair. Moreover, the occurrence of the (dd- and ll-) phase always coincides with the formation of yet another phase of the racemic compound containing four components in a crystal. Ostwald’s rule of stages here thus involves three steps and phases and is highly significant during the deracemization of the homochiral species., The evolution of the stereoisomeric system of rac-2-phenylglycinamide (PGA) and rac-N-acetyl tryptophan (NAT) follows a complex route involving three steps in Ostwald’s rule of stages. Deracemization requires termination of the process at the correct time, before more stable crystal forms develop.

Metal-organic frameworks (MOFs) have been a promising material for many applications, e.g., photocatalysis, luminescence-based sensing, optoelectronics, and electrochemical devices, due to their tunable electronic properties through linker functionalization. In this work, we investigate the effect of mixed organic linkers on the bandgap modulation of polymorphic zirconium-based MOFs, UiO-66 and MIL-140A using density functional theory (DFT) calculations. We show that the electronic properties of both MOFs are in contrast to Vegard's law for semiconductors, that is, mixed-linker systems exhibit bandgaps not intermediate within the range of single-linker systems. Calculations of the total and partial density of states revealed the formation of mid-gap states in mixed-linker MOFs, causing the bandgap reduction. Interestingly, although both MOFs have similar composition, the effect is more significant in MIL-140A than in UiO-66. This is due to the presence of π-π stacking interactions in MIL-140A, which does not occur in UiO-66. The simulation results reveal a direct relationship between the strength of π-π interactions and the bandgap. This illustrates that distinct structural features, particularly the orientation of organic linkers can give rise to different consequences in bandgap modulation. Moreover, this computational work highlights the possibility to engineer the electronic properties of MOFs through a mixed-linker approach.

Drug delivery from polymer nanocarriers is usually achieved by designing polymers so that they release drugs by cleavage of labile bonds, or by preparing nanoparticles that swell or collapse in response to external stimuli. Herein, we unravel the importance of polymer crystallinity in release profiles of drugs encapsulated in polymer nanoparticles. Polycaprolactone, as a model biocompatible and biodegradable semi-crystalline polymer, was processed into nanoparticles by the miniemulsion-solvent evaporation technique. The crystallinity of the nanoparticles was controlled by the polymer concentration, size of nanoparticles, and the composition of mixtures with amorphous polymers such as poly(vinyl formal) and polystyrene. Crystallinity decreased significantly with decreasing nanoparticle diameter. Release profiles of drugs were found to be dependent on an interplay of nanoparticle size and crystallinity. Therefore, crystallinity can be used for tuning the release profiles of nanoparticles.

Background Red lettuce has been consumed worldwide because it is a great source of natural antioxidants. To design a fertilizer formula to boost its nutritional value, this research simultaneously studied the effects of the significant cationic ions among the macronutrients for plant growth (K, Mg and Ca) and the effects of the electrical conductivity of the nutrient solution on the phenolic compounds production and mass productivity of hydroponically grown red lettuce. Results Red lettuce grown under the control treatment provided the highest mass productivity (under low stress conditions). The highest antioxidant content, measured as mg phenolic compounds per gram dry weight (at a high stress condition) via both Folin-Ciocalteu and HPLC analyses was observed in growth media containing 100 ppm K : 20 ppm Mg : 70 ppm Ca (with EC equal to 1241 μS⋅cm-1 ). It was found that EC within the range of this examination had no significant effect on the mass productivity nor the phenolic compounds productivity. The phenolic compounds productivity, defined as the amount of phenolic compounds produced per unit of planting area per unit of time, was optimized with the optimum formula for maximum phenolic compounds productivity of 90 ppm K : 29 ppm Mg : 77 ppm Ca, or a corresponding EC of 1307 μS⋅cm-1 . Conclusion The study demonstrates that health-promoting nutrient production in red lettuce could be stimulated in a practical manner by adjusting the cation concentrations in the fertilizer solution. This article is protected by copyright. All rights reserved.

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The population balance equation (PBE) has received an unprecedented amount of attention in recent years from both academics and industrial practitioners because of its long history, widespread use in engineering, and applicability to a wide variety of particulate and discrete-phase processes. However it is typically impossible to obtain analytical solutions, although in almost every case a numerical solution of the PBEs can be obtained. In this article, the symmetries of PBEs with homogeneous coagulation kernels involving aggregation, breakage and growth processes and particle transport in one dimension are found by direct solving the determining equations. Using the optimal system of one and two-dimensional subalgebras, all invariant solutions and reduced equations are obtained. In particular, an explicit analytical physical solution is also presented.

It is known that the antisolvents used for crystallization can affect the crystallization outcome and may promote the crystallization of a specific polymorph. In this study L-histidine (L-his) is used as a model substance, and ethanol was selected to be an antisolvent. The formation of the polymorphs of L-his in antisolvent crystallization as a function of supersaturation, ethanol volume fraction, and temperature was studied. The induction time for the antisolvent crystallization was also measured. The results showed that the induction time decreases with higher supersaturation and ethanol volume fraction, indicating that the nucleation rate of L-his from antisolvent crystallization (where water was used as the solvent and ethanol as the antisolvent) increases with higher supersaturation, as expected, and ethanol fraction. At all temperatures studied, the pure metastable polymorph B of L-his was obtained initially at higher ethanol volume fraction and supersaturation, while a mixture of the polymorphs A and B was obtained at lower ethanol volume fraction and supersaturation.

Centro de Investigación Forestal (CIFOR), TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl)-oxidized cellulose nanofibers (CNF) were assembled to fibrous clay sepiolite (SEP) by means of a high shear homogenizer and an ultrasound treatment followed by lyophilization using three different methods: normal freezing, directional freezing, and a sequential combination of both methods. Methyltrimethoxysilane (MTMS) was grafted to the foam surface by the vapor deposition method to introduce hydrophobicity to the resulting materials. Both the SEP addition (for the normal and directional freezing methods) and the refreezing preparation procedure enhanced the compressive strength of the foams, showing compressive moduli in the range from 28 to 103 kPa for foams loaded with 20% w/w sepiolite. Mercury intrusion porosimetry shows that the average pore diameters were in the range of 30-45 µm depending on the freezing method. This large porosity leads to materials with very low apparent density, around 6 mg/cm3, and very high porosity >99.5%. In addition, water contact angle measurement and Fourier-transform infrared spectroscopy (FTIR) were applied to confirm the foam hydrophobicity, which is suitable for use as an oil sorbent. The sorption ability of these composite foams has been tested using olive and motor oils as models of organophilic liquid adsorbates, observing a maximum sorption capacity of 138 and 90 g/g, respectively., This work was supported by Vidyasirimedhi Institute of Science and Technology (VISTEC), and funds (projects: MAT2015-71117-R and PID2019-105479RB-I00) from the Agencia Estatal de Investigación (AEI, Spain) and the FEDER Program (EU). R. M.-S. acknowledges the MINECO (Spain) for a “Juan de la Cierva-Incorporación” contract (IJCI-2016-28403) and B.W. thanks the AEI for a JIN project (PID2019-107022RJ-I00). Authors thank the Agencia Estatal CSIC (Spain) for supporting the Open Access publication.

Constructing invariant solutions of integro-differential equation.Group analysis of population balance equation.Preliminary group classification of an integro-differential equation. The integro-differential population balance equation describing aggregation processes was proposed almost 100 years ago. Aggregation is an important size enlargement process in many industries; the modeling and design of the process can be done using the population balance framework, however it is typically impossible to obtain analytical solutions: in almost every case a numerical solution of the equations must be obtained. In this paper, we present the developed group analysis method for the one-dimensional population balance equation for aggregation in a well-mixed batch system including a crystal growth term. The determining equations are solved, the optimal system, invariant solutions and all the reduced equations are obtained. Furthermore, finding the determining equation by use of the preliminary group classification is also considered.

Lysozyme was successfully separated from mixtures of lysozyme and ovalbumin by crystallization. The purity of the lysozyme product is more than 98%, the remaining activity is greater than 97%, and the yields of the crystal products were greater than 80%. The experimental conditions used were varied to study the effect of the operating parameters on the growth kinetics of lysozyme crystal and the separation ability of the process. The growth rates of lysozyme are second order with respect to the relative supersaturation. Therefore the growth kinetics of the crystallization process is controlled by the surface integration mechanism. The calculated growth rate constants were 5.4×10 −6 cm/h and 2.5×10 −6 cm/h for the crystallization process at 20 °C and 10 °C, respectively. There is no significant effect of the ovalbumin impurity up to the concentration of 67.5% ovalbumin (based on total protein) on the growth kinetics of lysozyme. Changing the NaCl concentration from 4% to 3% had no effect on the growth kinetics of lysozyme, although this does change the solubility and therefore the yield. The calculated activation energy was 53.08 kJ/mol which supports the hypothesis that the crystallization process is controlled by the surface integration mechanism.

This work aims to investigate synergy in anionic and zwitterionic surfactant mixtures, as they result in better interfacial properties and micellization behavior. Various mixtures of the pH-insensitive zwitterionic surfactant 3-(decyldimethylammonio) propanesulfonate (Zwittergent 3-10) and sodium dodecylsulfate (SDS) were prepared in aqueous solution at a range of pH values between 2 and 13. The thermodynamic parameters during mixed surfactant adsorption at the air/water interface are obtained and the results show the mixed surfactant systems having superior properties to the constituent surfactants. Experimentally, the mixed surfactant solutions clearly improve the surface activities by lowering the critical micelle concentration (CMC) and lowering the surface tension at the air/water interface. The synergisms are investigated through the interaction parameters estimated from regular solution theory that is used to quantitatively describe the nonideality of surfactant mixtures. High negative interaction parameters are obtained from these surfactant mixtures. Experimental precipitation phase boundaries of SDS in the presence of CaCl2 were also investigated in mixtures containing pH-insensitive zwitterionic surfactant at different pH levels from 2 to 13 and SDS mole fractions of 0.25, 0.50, 0.75, and 1.00. Changes in the precipitation phase boundaries are due to the changes in the speciation or activities of the major components both below and above the CMC. As a result, the precipitation phase boundaries are pH dependent. In addition, mixed micellization and counterion binding to the micelle also change the precipitation phase boundary above the CMC. The activity-based solubility product of calcium dodecylsulfate is also determined from the precipitation phase boundaries below the CMC. X-ray diffraction patterns and SEM images confirm that only calcium dodecylsulfate precipitates in the soap scum for all pH and surfactant compositions studied.

We describe a facile strategy to synthesize hybrid nanocapsules with an oil core for hindering interactions between payloads and silica shell. Polycaprolactone/silica nanocapsules are synthesized by an interfacial sol-gel process occurring simultaneously with internal phase separation of the polymer produced by a miniemulsion-solvent evaporation technique. The localization of the polycaprolactone in the nanocapsules is depending on the ratio between polymer and silica. Formation of hybrid nanocapsules is found to significantly hinder interactions of drugs such as ibuprofen and carbamazepine with the silica surface.

An improved process for the deracemization of a racemic conglomerate suspension of enantiomorphs has been created based on principles developed in an earlier method using temperature fluctuations. The method consists of circulating the suspension between two vessels, each controlled at a specific temperature in order to make the process more effective and faster to achieve a homochiral solid state. Crystals in the suspension were partially dissolved in the hot vessel, and the remaining crystals were regrown in the cold vessel. The crystals in the cold vessel have a longer residence time than those in the hot vessel to allow more time for the crystal growth process. The results show that complete deracemization can be achieved via this process far more rapidly than by using the previous temperature cycling (one-vessel) process. Moreover, the new process could easily be scaled up to an industrial scale. The current process can be an effective alternative to currently used enantiopurification methods, with s...

Population balance equations have been used to model a wide range of processes including polymerization, crystallization, cloud formation, and cell dynamics, but the lack of analytical solutions necessitates the use of numerical techniques. The one-dimensional homogeneous population balance equation with time dependent but size independent growth rate and time dependent nucleation rate is investigated. The corresponding system of equations is solved analytically in this paper.

This study investigates potential mechanisms affecting growth rate dispersion (GRD). Previous studies have identified surface roughness and internal lattice perfection as key mechanisms; this study investigates them both with respect to GRD. Crystal growth of potassium dihydrogen phosphate (KDP) was studied in two solvent mixtures, water and water-ethanol. The surface roughness was analyzed by atomic force microscopy (AFM) and the internal crystal perfection was analyzed by x-ray diffraction using a synchrotron source. The crystals grown at higher supersaturation have more pronounced and more frequent surface irregularities supporting previous findings on a feedback mechanism between surface roughness and growth rate. No significant relationship was seen between internal crystal perfection and growth rate, however, this is likely due to the size of the crystals analyzed in this study and not the absence of any such mechanism in small crystals.

A conventional all-in/all-out batch management, applied in most small to medium scale swine farming, often provides an inconsistent feed of wastewater for the biogas system, causing imbalance between the farm’s power requirement and its generation capacity. This study proposed two developed models that could be employed to ease this problem. In Model 1, the operation was divided into two batch intervals, while in Model 2, the operation used four separate batches. The developed models helped avoid an unnecessary long lag phase, allowing more stable anaerobic digestion performance, and a more evenly distributed amount of biogas being produced. Accordingly, the developed models more stably supplied energy for domestic use, achieving 36-44% reduction of the electricity expense, or a saving of 43,782 m3 biogas or 35,834 kWh equivalent compared with that of the conventional management. Moreover, excess biogas which occurred in the conventional management, up to 14,714 m3 or 12,043 kWh equivalent at the peak period, could be reduced by 79-100%, evaluated as a greenhouse gas reduction of 9,441 and 11,902 m3CO2eq by Models 1 and 2, respectively. This suggests that without additional investment, more profit could be attained from the significant reduction of operating cost by proper farm management.

This research aims to investigate the nucleation kinetics of the metastable polymorph B of L -histidine ( L -his). The nucleation rate of the metastable polymorph B of L -his was studied using water as a solvent and using various antisolvents to reduce the solubility and increase the supersaturation of L -his. Various methods can be used to determine the nucleation rate, e.g., induction time, metastable zone width, and direct measurement. However, direct measurement of the time evolution of the crystal size distribution by in-situ measurement is more suitable for scale-up purposes. The time evolution of the number of crystals was measured online via Focused Beam Reflectance measurement (FBRM). To investigate the nucleation rate, the antisolvent was added to the saturated solutions of L -his, then the crystals were allowed to nucleate under conditions of differing antisolvent type (methanol, ethanol, acetone, and acetonitrile), volume fraction of antisolvent to saturated solution (0.7 to 0.8), and the crystallization temperature (10, 25, and 40 °C). The nucleation rate increases with increasing volume fraction of antisolvent and supersaturation. The nucleation rate increases with higher temperature. The nucleation rates with acetonitrile and acetone antisolvents are very high whereas the nucleation rate with methanol is lowest because of the relatively high solubility of L -his in methanol at the same volume fraction. The interfacial energy of primary nucleation of the metastable polymorph B of L -his are different when using various antisolvents.

Preferential crystallization (PC) is a process to separate enantiomers. The efficiency of seeded, isothermal PC was enhanced using tailor-made additives to inhibit the crystallization of the counter-enantiomer. The inhibition of D-asparagine (D-Asn) monohydrate using D-glutamic acid (D-Glu) and D-aspartic acid (D-Asp) as additives in PC was investigated by comparing the purity, yield, and particle size distribution after PC of L-Asn·H2O from DL-Asn·H2O. The amount of pure L-Asn·H2O solid product that can be produced before crystallization of the counter-enantiomer is higher when using the additives D-Asp and D-Glu. However, the crystal size of L-Asn·H2O increases faster in PC without additives than in PC with additives. This means that the additives inhibit not only the crystallization of D-Asn·H2O but also the crystal growth of L-Asn·H2O.

Crystal growth rate dispersion (GRD) and size-dependent crystal growth (SDG) models are models to extend McCabe’s ΔL Law to more accurately account for variation in the crystal growth rates within a population of crystals. GRD is a phenomenon where the crystal growth rate either fluctuates randomly over time or varies over a population of crystals. SDG is where the growth rate of a crystal depends on its size, typically with growth rates assumed to increase monotonically with crystal size. Although it has been recognized for more than 30 years that, except for extremely small crystals, SDG is an artifact of GRD, it is still common in the literature for GRD in experimental results to be modeled using SDG models. This discussion will present some background and new experiments on the mechanism and extent of GRD to demonstrate that GRD is a real phenomenon, whereas SDG is largely an artifact, and some modeling work to demonstrate that SDG models cannot successfully replicate crystal size distribution data th...

Preferential Crystallization (PC) is a popular process to separate enantiomers, however the nucleation and growth of the counter enantiomer during the process can compromise the enantiopurity of the final crystalline product. This research investigates the use of additives to inhibit the nucleation and growth of the counter enantiomer. In this study, we use L-asparagine monohydrate (L-Asn·H2O) as the preferred enantiomer in crystallization from DL-Asn·H2O solutions. Additives include both pure enantiomers of several related amino acid species. This allows investigation of differences in inhibition caused by additives that are of the same chirality and different chirality as the preferred enantiomer. The additives had no discernible effect on the solubility but had a small effect on the metastable limit, with additives tending to slightly widen the metastable zone but also make the zone widths more disperse. D-additives have a small effect on the growth rate of L-Asn·H2O but L-Asp and L-Glu strongly inhibit the growth rate of L-Asn·H2O in DL-Asn·H2O solution; there must also be a corresponding effect for D-Asp and D-Glu on D-Asn·H2O. Indeed, PC experiments showed that in order to obtain L-Asn·H2O from a PC while preventing the formation of D-Asn·H2O, D-Asp and D-Glu are suitable additives, leading to high yield and purity of pure L-Asn·H2O.

Two simple models are proposed and tested for the mechanism of ripening of a conglomerate suspension to a single enantiomorph by temperature cycles. In both models, the initial crystal size distributions and masses of the two enantiomorphs are equal, but either the crystal growth rate or the growth rate distribution is varied. The difference in the crystal growth kinetics of the two enantiomorphs may be caused by the intrinsic thermodynamic stability of the crystals occurring in the initial suspension. The initial nucleation of one of the two enantiomers will occur earlier than that of the counter-enantiomer. This results in the formation of two populations occurring under different conditions, leading to different internal crystalline perfection and therefore different thermodynamic stability.

A deracemization technique using periodic temperature fluctuations on a conglomerate forming system undergoing a swift racemization in solution is demonstrated. The method uses heating and cooling periods of the suspension in order to create cycles of partial dissolution of the crystal phase followed by crystal regrowth: this enables symmetry breaking in the solid phase. The technique is an effective, simple, and cheap operation, and can promote understanding of the effects of dissolution and recrystallization on chiral symmetry breaking in the solid phase. The heating period leads to the decrease of the size of crystals and the destruction of small crystals; the surviving crystals can then grow during the cooling period. A succession of such cycles allows the autocatalytic transformation from a racemic suspension into pure enantiomer, with an enantiomeric excess (ee) > 99% within a few days. The results demonstrate a possible mechanism for the emergence of homochirality of molecules of biological signifi...

Experimental measurements of the solution-mediated transformation (SMT) of the metastable polymorph of DL-methionine (α-DL-met) into the stable polymorph (γ-DL-met) in water were performed at 25 °C. These results were compared to models of the crystallization and the SMT of α-DL-met into γ-DL-met that were developed using the concept of the population balance equation (PBE) applied to both of the polymorphs. The growth, dissolution, and nucleation kinetic expressions obtained in a previous work were used in the models. It was found that the PBE models did not satisfactorily describe the SMT process of DL-met when the measured crystallization and dissolution kinetics were used. There were large mismatches between the simulation and the experimental results. Modifying the model of the dissolution kinetics of α-DL-met enabled these mismatches to be lowered. The results showed that the SMT of DL-met is controlled by the rate of dissolution of α-DL-met.

Many of the chemical species prepared or purified using crystallization from solution exist in a number of polymorphic forms, and this can create challenges in the design and operation of industrial crystallizers, particularly where a polymorphically pure product is required. Where two or more polymorphs may crystallize from a solution simultaneously, the metastable polymorph may nucleate first, and will undergo a transformation to the stable polymorph over time. In a solution-based crystallizer the transformation between the metastable polymorph and the stable polymorph will usually occur via a solution mediated transformation (SMT) rather than a solid state transformation. Solution mediated transformation occurs via dissolution of the metastable polymorph crystals simultaneously with the nucleation and growth of the crystals of the stable polymorph. Theoretical models for these mechanisms (dissolution, nucleation, and growth) are all well known, and it is simple to measure the kinetic rates for fitting the models. An essentially exact model for the SMT can thus be created using a population balance model for each of the crystalline phases in the system, and this model can be parameterized based on models fitted using experimental data for the basic mechanisms. However to have a fully a priori model of the SMT is rarely attempted, and when it is it tends to be unsuccessful. More common is to use the nucleation or growth kinetics as fitted parameters in a model fitting the SMT data. This tends to fit the experimental data successfully but there is no guarantee that the model is fundamentally correct rather than simply a good fit to a set of data. Better a priori population balance models of the SMT should be achievable, however mechanisms which need to be better treated in the simulations include the induction time, crystal growth rate and dissolution rate dispersion, null supersaturation for crystal growth and null undersaturation for dissolution, the effect of crystal size and perfection on dissolution kinetics, and variations in crystal shape factors during the growth which may modify the mass balance terms in the model.

Attrition of crystals in industrial crystallization is the major source of secondary nucleation and has strong effects on product quality. This work describes attrition in industrial crystallizers using an empirical engineering model based on dimensionless groups describing crystal properties, suspension properties, and crystallizer geometry and operating conditions. Here the attrition rate of sodium chloride crystals in a small scale mixed-suspension crystallizer is studied, varying the following parameters: impeller speed, parent crystal size, suspension density, draft-tube impeller clearance, off-bottom impeller clearance, impeller type, and impeller material. It was found that the attrition rate depends on most of the variables investigated. The direction of the dependence is predictable based on intuitive modeling. An empirical power law model based on dimensionless groups predicted by Buckingham-Pi theory (using variables mentioned above) gives a good fit to the data.

Growth kinetics of the two common polymorphs of dl -methionine ( dl -met), α- dl -met and γ- dl -met, and dissolution kinetics of γ- dl -met, were studied in aqueous solution as part of an attempt to complete an a-priori model of the solution-mediated transformation (SMT) of polymorphs in this system, which will then be compared to measured rates of polymorph transformation. The growth rates of α- dl -met and γ- dl -met were found to be linearly dependent on the relative supersaturation of dl -met in the system. The dissolution rate of γ- dl -met was found to linearly depend on the relative undersaturation of dl -met in the system. Both the growth and dissolution rate constants are temperature dependent and follow an Arrhenius relationship. At all temperatures studied, both the growth rate of α- dl -met and the dissolution rate of γ- dl -met are faster than the growth rate of γ- dl -met, indicating that if the dissolution is a diffusion controlled process, then the SMT of the polymorphs of dl -met is likely to be controlled by the growth rate of γ- dl -met.

Optical resolution of dl -methionine hydrochloride ( dl -met·HCl) by preferential crystallization was studied for the purification of l -met·HCl (the desired enantiomer) from supersaturated solutions of dl -met·HCl. The nucleation thresholds (NT) of dl -met·HCl affect the maximum resolution time suitable for preferential crystallization and also the percentage purity of the product crystals. Crystal growth rates of l -met·HCl single crystals both in supersaturated solutions of dl -met·HCl and in supersaturated solutions of pure l -met·HCl were measured in order to model the preferential crystallization more effectively. Results showed that the growth rate depends strongly on the relative supersaturation (especially from pure l -met·HCl solutions), that there is a wide crystal growth rate distribution in growth from both types of solution, and that the growth is faster from pure l -met·HCl solutions, as expected. A batch crystallizer seeded with l -met·HCl crystals was used to study the preferential crystallization, and to study the behavior of purity decrease of the product crystals during the crystallization process. The purity of the l -met·HCl product decreased to the equilibrium value over time, with almost no plateau at 100% purity (as is hoped for in preferential crystallizations). This is explainable by the very short induction times for nucleation in these solutions, and also that the l -met·HCl seed crystals may act as a template for the nucleation of the counter-enantiomer.