Crystallization of Organic Compounds, 2nd Edition

Chapter 7Cooling Crystallization

Crystallization by cooling is commonly practiced for solutions in which solubility is a strong function of temperature. Cooling alone can achieve the desired degree of crystallization when solubility is sufficiently low at the termination of the cooling operation. In some cases, additional reduction in solubility is necessary to achieve the desired yield. This reduction can be accomplished by either evaporation or anti‐solvent addition, as discussed in Chapters 8 and 9.

Crystallization by cooling can be carried out in a batch or continuous operation. The reader is referred to Chapter 1 for a discussion of the advantages of each. In this chapter, a description of crystallization by batch cooling will be followed by a description of the continuous operation. As discussed in the introduction, a semi‐batch operation is one carried out with changes taking place (in volume, composition, etc.) which affect the critical parameters. An operation, or part of an operation, is considered semicontinuous if, during the operation, conditions in the processing unit being considered are unchanging.

7.1 BATCH OPERATION

A typical cooling operation, as described by Griffiths (1925), is shown in Figure 7.1. Solubility versus temperature is shown by A–B and the width of the metastable region is bounded by A–B and C–D. A solution at point E which is below the equilibrium saturation solubility is cooled until the temperature reaches the equilibrium solubility at ...