Kinetics industrial crystallizer applications

Tailoring of the particle size of the crystals from industrial crystallizers is of significant importance for both product quality and downstream processing performance. The scientific design and operation of industrial crystallizers depends on a combination of thermodynamics - which determines whether crystals will form, particle formation kinetics - which determines how fast particle size distributions develop, and residence time distribution, which determines the capacity of the equipment used. Each of these aspects has been presented in Chapters 2, 3, 5 and 6. This chapter will show how they can be combined for application to the design and performance prediction of both batch and continuous crystallization. 

Polymorphism and kinetics of crystallization of TAG and fat under static conditions (e.g., in differential scanning calorimetry [DSC] apparatus) have been studied for a long time and are summarized in many reviews (2-6). Yet, these conditions are far-removed from industrial applications, where crystallization is usually achieved under shear (dynamic). Shearing has a major effect on crystallization kinetics it induces a faster and more homogeneous crystallization, often in the stable form and with a refined grain size. Yet, its effect is far from being fully understood. Recently, several studies of dynamic crystallization of lipids have been reported (7-12). 

Hydrate crystal growth, unlike hydrate nucleation, is not a stochastic process. Hence, the intrinsic kinetics of hydrate growth can be studied experimentally and modeled. The intrinsic rate constant obtained for this process can be independent of the equipment used for its determination, if determined carefully with proper experimental design, and thus can be used for industrial or other applications. 

Precipitation or reactive crystallization is very common in industrial applications and laboratory practice. A large number of high-value added product and intermediate materials are produced via precipitation. The precipitation process is very complex and the properties of precipitate strongly depend on the kinetics of the component subprocesses and their conditions. All these factors, and also the fact that the typical size of precipitate is in the submicron to 100 fim range, make the precipitation process very unique. Frequently, different theoretical and experimental approaches than those used for typical crystallization are required. 

Batch crystallization has several desirable features and advantages in laboratory and industrial applications. Industrial batch crystallizers are commonly used to manufacture a wide variety of crystalline materials with desirable product features and quality. Laboratory batch crystallizers are often used to characterize crystallization kinetics and CSDs and to determine the effects of process conditions on these kinetics and CSDs. 

The synthesis of ammonia from its elements ranks as one of the most important discoveries in the history of the science of catalysis, not only because of its industrial application in which synthetic fertilizers have contributed enormously to the survival of mankind, but also from the viewpoint of fundamental science. Even today, some eighty years after the first demonstration of ammonia synthesis, many original scientific papers on the mechanism of the catalytic synthesis of ammonia are still published. Every time a new method, technique, or concept has appeared in the field of heterogeneous catalysis, it has been applied to this reaction. Specific examples of these applications over the years include the concepts of gas equilibrium, activated adsorption, structure sensitivitystoichiometric number and kinetic studies, " nonuniform surfaces, the measurements of surface area, surface composition and promoter distributions, and the use of isotopic and spectroscopic techniques. In particular, various surface science techniques have been applied successfully to this reaction system over well-defined single crystal surfaces in recent years. In this way the effect of promoters on the iron catalyst has been elucidated. Accordingly, the history of ammonia synthesis parallels not only that of industrial catalysis, but also the development of the science of catalysis. 

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