Influence of Taylor Vortex Flow on the Crystallization ofl-Glutamic Acid as an Organic Model Compound

Abstract

The mechanism of polymorph selection is still not fully understood in crystallization. This study demonstrates the impact of Taylor vortex flow on the crystallization and polymorph selection of l-glutamic acid as an organic model compound. Our results show that amorphous intermediates preceded the formation of a crystalline phase. The morphology of these amorphous precursors─ranging from spherical, oval, and ellipsoidal to irregular shapes─was governed by the velocity of the Taylor vortex flow. We attribute this observation to a transient liquidlike state of the amorphous precursor; simulations indeed corroborated this assumption as the morphology of droplets of a liquidlike precursor varies with the velocity of fluid motion accordingly. The phase selectivity depended on the intensity of the Taylor vortex flow. We found that the metastable α-form crystallized at low Taylor numbers, whereas the thermodynamically stable β-form was obtained at high Taylor numbers, suggesting an impact of Taylor vortex flow on the amorphous-to-crystalline rearrangement of the intermediates. Moreover, a critical value of the Taylor number as Ta ∼ 3636 was determined, which triggered the fast formation of the β-polymorph. We assume that the high shear rate and mass transfer of Taylor vortex flow facilitate the phase transformation from the α- to the β-polymorph.