In-situ monitoring and characterization of plug flow crystallizers

This work presents a study of a Roughton-type vortex mixer combined with a tubular reactor for the drowning out crystallization of benzoic acid from aqueous ethanol solutions using water as the antisolvent. Mixing times in vortex mixers have been shown to be as low as 1 ms and have also been found to be largely independent of the relative flow rates of inlet streams. This enables operation with larger anti-solvent ratios, without sacrificing mixing efficiency. Permitting the generation of higher supersaturations, and smaller particles, while also increasing flexibility of the system by broadening the range of compounds that can be used. Process analytical technologies (FBRM, PVM, ATR FT-IR) were applied in-situ in order to characterize crystallization via the use of a novel flow cell. A calibration-free method for concentration monitoring was successfully utilized to monitor the progress of the process. It was seen that the achievable particle size could be significantly reduced in size compared to batch operation, with a reduction in the square-weighted chord length from 152 to 52 mu m. For a given feed concentration, significant control over the product size within the plug flow crystallizer could be achieved, with an average square weighted chord length range of 52-87 mu m observed for the conditions investigated in this work. (C) 2012 Elsevier Ltd. All rights reserved.