Crystallization kinetics are characterized in terms of two dominant processes, nucleation kinetics and growth kinetics, occurring during crystallization from solution.
The governing equations of crystal growth and nucleation, also described in (J. Nývlt (1968) Kinetics of Nucleation in Solutions. Journal of Crystal Growth, 3 – 4, 377 – 383), show that the surface area of the crystal slurry plays an important role in determining crystal nucleation and growth kinetics. At the start of a crystallization process, the surface area of crystals present in the slurry is low – meaning nucleation can dominate over growth, regardless of other kinetic factors. As crystallization proceeds, the surface area increases and it is possible for growth kinetics to become more favorable. When a linear cooling rate is applied (as shown on the right) to a crystallization process, it is possible for supersaturation to build up initially when there is no surface area available for growth. This build up results in fast, and often, unpredictable crystallization kinetics – with nucleation often dominating.
A clever technique for enhancing growth is to cool very slowly at first, when surface area is limited (as shown on the right). This keeps supersaturation low and allows growth to dominate. After some time, when surface area has increased, the cooling rate can be increased, reducing batch time, while still favoring growth. This technique strikes the right balance between controlling supersaturation and excessive nucleation, while avoiding very long batch times (P. Barrett, B. Smith, J. Worlitschek, V. Bracken, B. O’Sullivan, and D. O’Grady 2005) A Review of the Use of Process Analytical Technology for the Understanding and Optimization of Production Batch Crystallization Processes. Organic Process Research & Development, 9(3), 348 – 355). One drawback from this approach is that implementing a non-linear cooling or anti-solvent addition profile in the plant can be difficult and adds complexity to a process. However, success can still be achieved by using a small number of linear ramps, which achieve a similar result.
The value of implementing non-linear cooling rates to keep supersaturation constant over the course of a process has been proven by implementing a control loop that adjusts process temperature in order to keep supersaturation constant. Such a result was described in V. Liotta and V. Sabesan (2004) Monitoring and Feedback Control of Supersaturation Using ATR-FTIR to Produce an Active Pharmaceutical Ingredient of a Desired Crystal Size. Organic Process Research & Development, 8(3), 488 – 494. Copyright (2004) American Chemical Society, where a control algorithm is used to perform a crystallization process at constant supersaturation (shown on the left). In this example, supersaturation is monitored using in situ FTIR monitoring and the resulting temperature profile is non-linear: slow at first, and fast towards the end.
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:
Výsev je jedním z nejdůležitějších kroků při optimalizaci chování krystalizace. Při navrhování strategie setí je třeba vzít v úvahu parametry, jako je velikost osiva, zatížení osiva (hmotnost) a teplota přidávání osiva. Tyto parametry jsou obecně optimalizovány na základě kinetiky procesu a požadovaných konečných vlastností částic a musí zůstat konzistentní během zavádění do praxe a přenosu technologií.
Změna měřítka nebo podmínek míchání v krystalizátoru může přímo ovlivnit kinetiku procesu krystalizace a konečnou velikost krystalu. Účinky přenosu tepla a hmoty je důležité vzít v úvahu u chladicích systémů a systémů proti rozpouštědlům, kde teplotní nebo koncentrační gradienty mohou způsobit nehomogenitu v převládající úrovni přesycení.
Krystalizátor MSMPR (Mixed Suspension Mixed Product Removal) je typ krystalizátoru používaného v průmyslových procesech k výrobě vysoce čistých krystalů.
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.
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.
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 protocols and the 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).
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.
Lactose crystallization is an industrial practice to separate lactose from whey solutions via controlled crystallization.
Krystalizace proteinů je proces a metoda vytváření strukturovaných, uspořádaných mřížek pro často složité makromolekuly.
Liquid-Liquid phase separation, or oiling out, is an often difficult to detect particle mechanism that can occur during crystallization processes.
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.
Crystal polymorphism describes the ability of one chemical compound to crystallize in multiple unit cell configurations, which often show different physical properties.
Přesycení nastává, když roztok obsahuje více rozpuštěné látky, než by mělo být termodynamicky možné vzhledem k podmínkám systému. Přesycení je považováno za hlavní hnací sílu krystalizace.
Recrystallization is a technique used to purify solid compounds by dissolving them in a hot solvent and allowing the solution to cool. During this process, the compound forms pure crystals as the solvent cools, while impurities are excluded. The crystals are then collected, washed, and dried, resulting in a purified solid product. Recrystallization is an essential method for achieving high levels of purity in solid compounds.
Výsev je jedním z nejdůležitějších kroků při optimalizaci chování krystalizace. Při navrhování strategie setí je třeba vzít v úvahu parametry, jako je velikost osiva, zatížení osiva (hmotnost) a teplota přidávání osiva. Tyto parametry jsou obecně optimalizovány na základě kinetiky procesu a požadovaných konečných vlastností částic a musí zůstat konzistentní během zavádění do praxe a přenosu technologií.
Změna měřítka nebo podmínek míchání v krystalizátoru může přímo ovlivnit kinetiku procesu krystalizace a konečnou velikost krystalu. Účinky přenosu tepla a hmoty je důležité vzít v úvahu u chladicích systémů a systémů proti rozpouštědlům, kde teplotní nebo koncentrační gradienty mohou způsobit nehomogenitu v převládající úrovni přesycení.
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.
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).
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.
Recrystallization is a technique used to purify solid compounds by dissolving them in a hot solvent and allowing the solution to cool. During this process, the compound forms pure crystals as the solvent cools, while impurities are excluded. The crystals are then collected, washed, and dried, resulting in a purified solid product. Recrystallization is an essential method for achieving high levels of purity in solid compounds.
