Changing the scale or mixing conditions in a crystallizer can directly impact the kinetics of the crystallization process and the final crystal size. Heat and mass transfer effects are important to consider for cooling and anti-solvent systems respectively, where temperature or concentration gradients can produce inhomogeneity in the prevailing level of supersaturation. This often results in pockets of very high supersaturation close to the walls of the vessel for a cooling crystallization, or at the addition location for anti-solvent (and also reactive) crystallizations.
Pockets of high supersaturation can cause very high nucleation and growth rates in certain regions of a large scale crystallizer, meaning the final crystal size distribution could vary dramatically from that achieved in a better-mixed environment in the lab during development. As seen in the graph to the right, a change from a 500 mL reactor to a 2 L reactor for the same crystallization process results in unexpected nucleation events characterized by ParticleTrack. Also, the number of fines generated throughout the batch is significantly higher.
The effect of local supersaturation build-up on crystallization is shown here, where the repeatability of the nucleation point for an unseeded crystallization is shown for an anti-solvent crystallization system. For this process (right), when anti-solvent is added above the liquid surface and near the wall of the reactor, especially at higher addition rates, the nucleation point is extremely inconsistent, with wide error bars shown for these experiments that were conducted in triplicate (D. O’Grady, M. Barrett, E. Casey, and B. Glennon. (2007) The Effect of Mixing on the Metastable Zone Width and Nucleation Kinetics in the Anti-solvent Crystallization of Benzoic Acid. Chemical Engineering Research and Design, 85, 945 – 952). Additionally, when adding anti-solvent above surface and at the wall of the crystallizer, nucleation consistently occurs sooner, at lower anti-solvent concentrations. The reason for these two concerning results is that when anti-solvent is added close to the wall, the mixing conditions in the crystallizer make it difficult for the anti-solvent to be incorporated easily, and supersaturation builds up at the feed location.
The reason for this dramatic disparity in consistency is due to how anti-solvent is incorporated into the vessel. This video (left) show computational fluid dynamics (CFD) tracer experiments, for both addition locations shown above (center and wall). When anti-solvent is added above the surface and close to the wall, it is difficult to effectively incorporate the liquid into the bulk solution. When anti-solvent is added closer to the impeller, incorporation of the anti-solvent occurs immediately. For this crystallization system this difference in anti-solvent incorporation – and the associated difference in the homogeneity of supersaturation through the vessel – causes significant differences in the nucleation and consistency of the crystallization process .
In addition to mass transfer effects, the shear rate in a crystallizer can have a physical impact on the crystals through breakage. Crystal breakage is a function of the solids concentration in the system as well as the shear rate. As scale and mixing conditions change - solids concentration and shear rate gradients may become important, meaning more or less breakage could occur as a crystallization process is scaled up. In this example (right), the chord length distributions acquired using FBRM technology (ParticleTrack) for a continuous crystallization process, are shown for three different agitation intensities (E. Kougoulos, A.G. Jones, and M.W. Wood-Kaczmar (2005) Estimation of Crystallization Kinetics for an Organic Fine Chemical Using a Modified Continuous Cooling Mixed Suspension Mixed Product Removal (MSMPR) Crystallizer, Journal of Crystal Growth, Volume 273, Issues 3 – 4, 3 January 2005, Pages 520 – 528). As agitation and the associated shear rate increase, the distributions shift to the left with an increase in fine crystal counts, indicating crystal breakage. This result is common. However, such behavior is difficult to predict as the volume changes, since agitation intensity is not a scalable parameter.
This paper discusses common particle size analysis techniques and how they are used for the delivery of high-quality particles. Examples include the usage of offline particle size analyzers in combination with in-process particle characterization tools to optimize processes.
Crystallization unit operations offer the unique opportunity to target and control an optimized crystal size and shape distribution to:
Crystal polymorphism describes the ability of one chemical compound to crystallize in multiple unit cell configurations, which often show different physical properties.
Herkristallisatie zorgt voor kristalproducten met de gewenste fysieke eigenschappen. Hier vindt u alle informatie ende zeven stappen van het ideale herkristallisatieproces.
Solubility curves are commonly used to illustrate the relationship between solubility, temperature, and solvent type. By plotting temperature vs. solubility, scientists can create the framework needed to develop the desired crystallization process. Once an appropriate solvent is chosen, the solubility curve becomes a critical tool for the development of an effective crystallization process.
Wetenschappers en technici kunnen kristallisatieprocessen beheersen door het niveau van oververzadiging tijdens het proces zorgvuldig aan te passen. Oververzadiging is de drijvende kracht voor kristalnucleatie en -groei en bepaalt de uiteindelijke verdeling van de kristalgrootte.
In-process probe-based technologies are applied to track particle size and shape changes at full concentration with no dilution or extraction necessary. By tracking the rate and degree of change to particles and crystals in real time, the correct process parameters for crystallization performance can be optimized.
Seeding is one of the most critical steps in optimizing crystallization behavior. When designing a seeding strategy, parameters such as seed size, seed loading (mass), and seed addition temperature must be considered. These parameters are generally optimized based on process kinetics and the desired final particle properties, and must remain consistent during scale-up and technology transfer.
Liquid-Liquid phase separation, or oiling out, is an often difficult to detect particle mechanism that can occur during crystallization processes.
In an antisolvent crystallization, the solvent addition rate, addition location and mixing impact local supersaturation in a vessel or pipeline. Scientists and engineers modify crystal size and count by adjusting antisolvent addition protocol and the level of supersaturation.
Crystallization kinetics are characterized in terms of two dominant processes, nucleation kinetics and growth kinetics, occurring during crystallization from solution. Nucleation kinetics describe the rate of formation of a stable nuclei. Growth kinetics define the rate at which a stable nuclei grows to a macroscopic crystal. Advanced techniques offer temperature control to modify supersaturation and crystal size and shape.
Changing the scale or mixing conditions in a crystallizer can directly impact the kinetics of the crystallization process and the final crystal size. Heat and mass transfer effects are important to consider for cooling and antisolvent systems respectively, where temperature or concentration gradients can produce inhomogeneity in the prevailing level of supersaturation.
Protein crystallization is the act and method of creating structured, ordered lattices for often-complex macromolecules.
Lactose crystallization is an industrial practice to separate lactose from whey solutions via controlled crystallization.
A well-designed batch crystallization process is one that can be scaled successfully to production scale - giving the desired crystal size distribution, yield, form and purity. Batch crystallization optimization requires maintaining adequate control of the crystallizer temperature (or solvent composition).
Continuous crystallization is made possible by advances in process modeling and crystallizer design, which leverage the ability to control crystal size distribution in real time by directly monitoring the crystal population.
The MSMPR (Mixed Suspension Mixed Product Removal) crystallizer is a type of crystallizer used in industrial processes to produce high-purity crystals.
Solubility curves are commonly used to illustrate the relationship between solubility, temperature, and solvent type. By plotting temperature vs. solubility, scientists can create the framework needed to develop the desired crystallization process. Once an appropriate solvent is chosen, the solubility curve becomes a critical tool for the development of an effective crystallization process.
In-process probe-based technologies are applied to track particle size and shape changes at full concentration with no dilution or extraction necessary. By tracking the rate and degree of change to particles and crystals in real time, the correct process parameters for crystallization performance can be optimized.
Seeding is one of the most critical steps in optimizing crystallization behavior. When designing a seeding strategy, parameters such as seed size, seed loading (mass), and seed addition temperature must be considered. These parameters are generally optimized based on process kinetics and the desired final particle properties, and must remain consistent during scale-up and technology transfer.
Crystallization kinetics are characterized in terms of two dominant processes, nucleation kinetics and growth kinetics, occurring during crystallization from solution. Nucleation kinetics describe the rate of formation of a stable nuclei. Growth kinetics define the rate at which a stable nuclei grows to a macroscopic crystal. Advanced techniques offer temperature control to modify supersaturation and crystal size and shape.
Changing the scale or mixing conditions in a crystallizer can directly impact the kinetics of the crystallization process and the final crystal size. Heat and mass transfer effects are important to consider for cooling and antisolvent systems respectively, where temperature or concentration gradients can produce inhomogeneity in the prevailing level of supersaturation.
A well-designed batch crystallization process is one that can be scaled successfully to production scale - giving the desired crystal size distribution, yield, form and purity. Batch crystallization optimization requires maintaining adequate control of the crystallizer temperature (or solvent composition).