Experimental study and simplified mathematical description of preferential crystallization.

The purpose of this paper is to investigate the concept of preferential crystallization, with a focus on aspects of quantification and application from an engineering point of view. The amino acid threonine was used as a model system in the experiments performed. Application of on-line polarimetry in combination with measurements of an on-line density meter proved the general applicability of this method in order to monitor directly the resolution progress, to recognize the region of "safe" resolution, and to gain information about the crystallization kinetics. For evaluation of the crystal growth kinetics of the desired enantiomers, the method of moments was applied to analyze isothermal single-step crystallization experiments. A population balance model is used in order to simulate the time changes of liquid-phase composition during the preferential crystallization process. Finally, preliminary experimental results regarding the cyclic operation mode are presented.