Influence of Fluid Motions on Polymorphic Crystallization of l-Histidine: Taylor Vortex Flow and Turbulent Eddy Flow

Abstract

The mechanistic influence of fluid motions, such as a Taylor vortex flow and turbulent eddy flow, on the polymorphic crystallization of l-histidine was investigated. Couette–Taylor (CT) and mixing tank (MT) crystallizers were used for the Taylor vortex flow and turbulent eddy flow, respectively. Due to its periodic fluid motion, the Taylor vortex flow was found to be more favorable than the turbulent eddy flow for polymorphic nucleation of the stable phase. Thus, the polymorphic fraction of the stable phase at the induction point (called the “initial stable polymorphic fraction”) in the CT crystallizer was always much higher than that in the MT crystallizer for all variations of the crystallization conditions, including the rotation/agitation speed, ethanol fraction in the mixture solvent, and cooling rate. When increasing the rotation speed of the inner cylinder in the CT crystallizer, the initial stable polymorphic fraction was significantly increased and reached 100% at a rotation speed above 700 rpm. ...