Cocrystallization of Caffeine-Maleic Acid in a Batchelor Vortex Flow

Here, the influence of Batchelor vortex flow on the cocrystallization of caffeine (CAF) and maleic acid (MA) is studied and compared with that of turbulent eddy flow. Batchelor flow, induced in a rotating disk (RD) crystallizer, is a periodic pattern of vortex motion, whereas turbulent flow, generated in a mixing tank (MT) crystallizer, is a random eddy motion. Typically, the cocrystallization in an MT crystallizer proceeds in such a way that a metastable nucleation of a 2:1 cocrystal occurs first, followed by stable nucleation of a 1:1 cocrystal. Then, the 2:1 metastable cocrystal is transformed into a 1:1 stable cocrystal through the reconstruction process in solution. However, in an RD crystallizer, stable nucleation is directly induced to generate a 1:1 cocrystal because Batchelor vortex flow is effective for the viscous frictional dissipation and molecular alignment in solution. Therefore, the induction of cocrystal nucleation in an RD crystallizer is always faster than that in an MT crystallizer during the variation in rotation/agitation speed, feed concentration, and cooling rate. On the basis of the obtained results, it is inferred that the cocrystal nucleation at various stoichiometric ratios depends on the flow velocity and flow patterns.