Polymorphic Crystallization of Sulfamerazine in Taylor Vortex Flow: Polymorphic Nucleation and Phase Transformation

The influence of a periodic Taylor vortex flow on the polymorphic crystallization of sulfamerazine (SMZ), including polymorphic nucleation and phase transformation, was investigated using a Couette-Taylor (CT) crystallizer; and also compared with the influence of a random turbulent flow in a mixing tank (MT) crystallizer. In the MT crystallizer, the induction of the metastable phase (form-I) occurred first, which was then followed by the induction of the stable phase (form-II) 10-85 h later. However, this whole process was significantly reduced to a half hour in the CT crystallizer, demonstrating the high efficiency of a, Taylor vortex flow for the Induction of polymorphic nucleation. The efficiency of the Taylor vortex flow was also enhanced when increasing the rotation speed. As a result, the stable and metastable phases were simultaneously nucleated at the first induction with a rotation speed above 300 rpm; plus the stable-phase fraction nucleated at the first induction increased when increasing the rotation speed. In addition, the polymorphic nucleation was facilitated when decreasing the dimension of the Taylor vortex flow, which was proportional to the gap size between the inner and outer cylinders. The periodic Taylor vortex flow was also more effective than the random turbulent flow for the phase transformation from the metastable phase to the stable phase. Thus, the dine period for the complete phase transformation (called the reconstruction time) in the CT crystallizer was 5-10 times shorter than that in the MT crystallizer. Furthermore, the phase transformation was enhanced when decreasing the dimension of the Taylor vortex due to the promotion of the mass transfer. Finally, the polymorphic nucleation and phase transformation that varied with the rotation speed and gap size of the CT crystallizer were linearly correlated with one parameter: the viscous energy dissipation, representing the hydrodynamic intensity of the Taylor vortex flow.