Controlling Crystal Growth Department Editor: Rita L. D’Aquino Chemical Engineering Magazine

**Manfenix** Vie Abr 15, 2011 1:42 pm

The formation of crystals requires the birth of new particles, also called nucleation, and the growth of these particles to the final product size. The driving force for both rates is the degree of supersaturation, or the numerical difference between the concentration of solute in the supersaturated solution in which nucleation and growth occurs vs. concentration of solute in a solution that is theoretically in equilibrium with the crystals.
In a batch crystallizer, the crystal size distribution (CSD) is controlled by first seeding the initially supersaturated batch with a known number and size distribution of crystals, and then controlling the rate of evaporation or cooling (i.e., rate of energy transfer) so as to achieve a level of supersaturation that supports adequate crystal growth and an acceptable rate of nucleation.

The relationship between supersaturation and growth is linear, but that between nucleation and growth is raised to a power that is usually greater than one, making it difficult to grow large crystals when nucleation is occurring.

The following procedure describes how to achieve the optimal growth rate:

1. Screen the seeds at the beginning of the experiment to determine the cumulative number of crystals that are greater than a given size N’. Estimate NLi, the number of crystals of a given size (Lav) obtained from the screening:

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Controlling Crystal Growth Department Editor: Rita L. D’Aquino Chemical Engineering Magazine 2q1avx10