Crystallization of Organic Compounds, 2nd Edition

Chapter 8Evaporative Crystallization

8.1 INTRODUCTION

Increasing the concentration by evaporation or distillation is a common method for increasing supersaturation and inducing crystallization. Since solvent is removed over a finite period of time, it is inherently a semibatch operation. Semicontinuous or continuous operation is also possible. The evaporation or distillation can be run at atmospheric pressure or at reduced pressure when substrate stability is not compatible with the required atmospheric distillation temperature.

One of the primary advantages of evaporative procedures is that they can often be combined with other process operations to reduce equipment requirements and/or time cycles. In addition, it is possible in some cases to complete the crystallization without the addition of a second solvent, thereby avoiding the costs of separation and recovery. Some of the process advantages that may be realized are as follows:

• Combination with a change in solvent and simultaneous crystallization.
• Combination with reaction and removal of a volatile reaction by‐product and simultaneous crystallization.
• Combination with cooling crystallization.
• Combination with antisolvent crystallization.

These operational advantages must be evaluated against the disadvantages that are discussed in the sections to follow. These disadvantages may include

• difficulty in controlling mean particle size and particle size distribution (PSD)
• difficulty in determining the seed point
• unpredictability ...