On the distribution and movement of impurities in crystalline layers in melt crystallization processes

Abstract

Melt crystallization processes by solid layer techniques are predominantly used to purify organic materials. On top of the separation by the actual crystallization process a further purification can be achieved by additional sweating and/or washing operations. However, both operations depend strongly on the previous crystallization process. To understand the two mentioned operations it is necessary to know the impurity distribution within a crystalline layer prior to their application. Another question is what happens within the layer when the operations are executed. The authors present experimental results for the impurity distribution within crystal layers in laboratory equipment (tube crystallizer of 1.5 m length, with the crystalline layers on the inside or the outside). Different growth rates and fluid dynamic conditions as well as two distinct systems (materials) are other varied parameters. First explanations for the experimental data are also given. These explanations can help both the understanding of the phenomena and the modelling of solid layer processes.