Bypass-driven particle size classification in a taylor-couette crystallizer

Continuous crystallization of pharmaceutical compounds requires precise control of the particle size distribution, whereby the particles’ residence time distribution plays a crucial role. The vortex flow in a Taylor-Couette crystallizer enables size-dependent spatial particle segregation, promising inline particle size classification. In this study, we investigated the particle size-dependent residence time distribution in a horizontally oriented Taylor-Couette Crystallizer, operated in the turbulent Taylor vortex flow regime. Bimodal particle suspensions were injected as the tracer, and the pulse response was continuously monitored using a QICPIC online imaging system for PSD analysis, equipped with a custom-made 3D-printed flow cell designed for volume flow rates below 100 mL∙min −1 . Within the framework of a design of experiments, we first quantified the impact of volume flow rate and rotation rate on the vortex drift velocity ratio, which serves as an indicator of bypass intensity, assumed to be the primary driver of size classification. Our results show that decreasing the vortex drift velocity ratio reduces the mean particle residence time, with the effect more pronounced for larger particles, clearly demonstrating a particle-size-classifying effect in Taylor vortex flow.