Abstract
The influence of intensity Taylor vortex flow in Couette-Taylor crystallizer on the crystallization of polymorphic amino acid L-glutamic acid was investigated in cooling crystallization. Here, the L-glutamic acid was chosen as the model crystal product, where it has two kinds of polymorphism including the unstable phase α-form and stable phase β-form crystal. In cooling crystallization, the α-form crystal transformed to the β-form crystal corresponding to the phase transformation of α-form to β-form crystal. The present study found that the selective polymorphism of α-form and β-form crystal as well as the phase transformation significantly depended on the intensity of turbulent Taylor vortex flow in Couette-Taylor crystallizer. Here, the selective β-form nucleation and phase transformation were remarkably promoted as increasing the rotation speed of inner cylinder in Couette-Taylor crystallizer. By comparison with the conventional stirred tank (ST) crystallizer, the Couette-Taylor (CT) crystallizer was at least 2.0 times more effective as regards the selective β-form polymorphism and phase transformation time. The advantage of CT crystallizer over the conventional ST crystallizer was explained in terms of the high shear stress and mass transfer of turbulent Taylor vortex flow in CT crystallizer. Here, the shear stress of Taylor vortex flow in CT crystallizer was at least 23.0 times higher than that of fluid motion in conventional ST crystallizer, whereas the mass transfer of Taylor vortex flow in CT crystallizer was at least 1.2 times higher than that of fluid motion in conventional ST crystallizer. As such, the high turbulent shear stress of Taylor vortex flow was expected to promote the β-form nucleation via the effective molecules alignment, whereas the high mass transfer of Taylor vortex flow facilitated the dissolution rate of α-form and growth rate of β-form crystal, resulting in an acceleration of phase transformation rate.
Highlights
Crystallization is a significant separation, purification and particle technology used in various life science industries including pharmaceuticals, foods and fine chemicals, etc
The fluid hydrodynamic of Couette-Taylor crystallizer should be clearly understood before investigating the crystallization
It is expected that the Couette-Taylor crystallizer will be more effective than the stirred tank crystallizer as regards the amino acid L-glutamic acid crystallization
Summary
Crystallization is a significant separation, purification and particle technology used in various life science industries including pharmaceuticals, foods and fine chemicals, etc. In the polymorphic organic and inorganic material crystallization, the Couette-Taylor crystallizer has been already applied in order to control the selection and phase transformation of polymorphic crystal. The crystallization of amino acid L-glutamic acid has been carried out, most of them were conducted in the conventional stirred tank crystallizer, where the phase transformation of unstable phase α-form to stable phase β-form required an extreme long crystallization time. In contrast to previous studies, the CouetteTaylor crystallizer in our current work was developed to facilitate the polymorphic crystallization of L-glutamic acid, where the dependency of selective polymorph and phase transformation on the intensity Taylor vortex flow in Couette-Taylor crystallizer was deeply investigated. According to Biradha et al [19-20], the crystallization research is not found in the South and East Asian countries including Vietnam, Indonesia, Philippine, Malaysia, etc, meaning that the crystallization research should be developed in the South and East Asian countries
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