(177g) Microwave Assisted Crystallization: Intensification of Direct Nucleation Control

Direct nucleation control (DNC) is a feedback control strategy used to control the size distribution of crystals (one of the many possible control objectives) during a crystallization process. DNC has been shown for maintaining a narrow size distribution by removal of unwanted fine particles. Application of DNC for obtaining desired size distribution is based on alternating dissolution and growth cycles, achieved via temperature cycling and triggered as a result of deviations in the particle count set point (measured by in-situ measurement PAT tool).

However, a major draw-back of the DNC implemented in conventionally heated/cooled reactors is that the temperature cycles needed to dissolve the nuclei considerably increases the process/batch time. However recently it has been demonstrated that by application of microwave fields for heating, the same control performance can be achieved with a 50% reduction in process/batch time. The study showing the intensification of the DNC in terms of process time by integrating microwave fields into a crystallizer was performed in a 1 litre jacket vessel in which the slurry was circulated via an external loop through a microwave cavity. However a better application would be when microwave fields are truly introduced inside the crystallizer thus eliminating external loops for slurry circulation which can be problematic.

In this study we present DNC experiments using a microwave integrated crystallizer. The crystallizer utilizes internal transmission line technology made available by Sairem SAS which enables direct introduction of microwave fields into the slurry. In this study we demonstrate cooling crystallization with DNC control and address key challenges in process integration and implementation, namely: Evaluation and optimization of the microwave heating to ensure homogeneous temperature distribution in the system, Optimization of the reactor configuration for safe introduction of PAT tools essential for DNC feedback (e.g FBRM), by avoiding the exposure to high intensity MW field and evaluation of the performance of microwave assisted DNC in a cooling crystallization process.