Semibatch cooling crystallization

Table 14.3 Optimization variables for batch and semibatch cooling crystallization.

Just as a reactor can be operated in batch or semibatch mode, a crystallizer can also be operated in batch or semibatch mode. Table 14.3 contrasts the optimization variables for batch and semibatch operation of cooling crystallization. 

The difference between batch, semibatch, continuous, and semicontinuous processing was discussed in Chapter 1. Continuous processes are characterized by parameters which may be geographically distributed within the system but are unchanging with time. Continuous crystallizers are in common use throughout the chemical process industries, but are less so in the pharmaceutical and fine chemical industries because of the typically smaller amounts to be processed. This section on continuous cooling crystallization will discuss continuous operation and point out the differences from batch/semibatch operation described above. It will also illustrate some strategies and equipment types used for these operations. 

Cooling after completion of the semibatch addition can proceed without concern for nucleation because 50% of the product is present as crystals, thereby providing a large growth area and avoiding excessive supersaturation. 

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