Effect of Supersaturation Control and Heterogeneous Nucleation on Porous Membrane Surfaces in the Crystallization of l-Glutamic Acid Polymorphs

This paper describes the crystallization of L-glutamic acid polymorphs in both quiescent and forced solution flow membrane crystallizers. The b polymorph was selectively obtained in static conditions, while the R form was preferentially grown in dynamic configuration, depending on the rate of solvent removal. According to concepts of the classical nucleation theory, the nucleation rate of the two polymorphs ± and b have been calculated taking into account the quiescent/forced solution fluid dynamics regime and the homogeneous/heterogeneous nucleation activation mechanism. By this approach, the number-based polymorph fraction a, which is considered as an indication of the chance for a specific polymorphs to nucleate, was calculated. On these bases, the effect of supersaturation control and heterogeneous nucleation on the porous membrane surface was analyzed. Theoretical calculations have been compared with the experimental polymorphic outcome of the crystallization of L-glutamic acid (LGA) and an appropriate crystallization mechanism, for the different operative environments, has been formulated. Although it is obvious, classical theory was a helpful tool in describing experimental results obtained in the membrane-based equipment.