On how non-facetted crystals affect crystallization processes

Abstract

In crystallization processes, suspensions are agitated in order to equilibrate concentration and temperature gradients. Crystal/stirrer, crystal/crystal and/or crystal/wall collisions lead to abrasion and secondary nucleation and hence to non-facetted crystals. While abrasion and growth are studied quite well individually in the literature, their interaction is not well understood. In addition, crystals are usually assumed to be facetted. We hypothesize that this assumption is not valid when damaged crystals grow. Therefore, in this contribution, we aim at understanding the interaction of crystal growth and abrasion on process scale under consideration of non-facetted crystals. We use recently developed and experimentally validated models for growth and abrasion simulations of abraded crystals on a single crystal scale, to derive suitable advection rates for a three dimensional population balance model (PBM). On the process scale, the PBM then considers the effects of growth and abrasion on crystal shape and vice versa. PBM simulations show that non-ideal shape increases the overall volume growth rate not only through an increase in overall surface area but also because it yields fast growing surface. We discuss our results in context of how neglecting shape may lead to misinterpretation of experimental data. For this purpose we explain that our approach explains apparent growth rate dispersion through non-facetted crystal shapes.