10 - Batch crystallization

Abstract

Batch crystallization is different from continuous crystallization in that the withdrawal of crystal product for the batch system is made only once at the end of the batch run. Batch crystallization may also include the semibatch system in which one or more feed solutions are continuously added to the crystallizer. Batch crystallization is commonly used in the chemical, pharmaceutical, and photographic industries as a manufacturing process to prepare a wide variety of crystalline products. 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 crystal size distribution (CSD) and to determine the effects of process conditions on these kinetics and CSDs. Several factors affecting batch crystallization are discussed in this chapter. These include batch cycle time, supersaturation profile, external seeding, fouling control, CSD control, growth rate dispersions, and mixing. The control of supersaturation must be employed in batch crystallization to obtain a desired CSD of the product. If the crystals are growing very slowly, a batch process can be controlled more easily to produce larger crystals than in a continuous process. In addition, batch crystallizers produce a narrower CSD than the continuous well-mixed crystallizers. Thus, if monodisperse crystals are needed, batch crystallization offer significant advantages in meeting the product requirement.