Selective Glycine Polymorph Crystallization by Using Microporous Membranes

The selective crystallization of either R or ç polymorph of glycine was obtained by both static and dynamic membrane crystallization. The membrane matrix acts as a selective medium for solvent evaporation by modulating the rate for the achievement of supersaturation. In static membrane system this was obtained by changing the concentration of the stripping solution inside the membrane fibers, whereas in dynamic configuration it was obtained by varying the recirculation solution velocity. The increase in solvent evaporation rate induced an increase in the metastable zone width with effects on the heat and mass transfer during the nucleation kinetics. The consequent switching between a thermodynamically and a kinetically controlled nucleation stage resulted in the production of either a stable or metastable form of glycine. As control of polymorphism is critical in many pharmaceutical, electronic, and food applications, the possibility of inducing polymorph selection during a crystallization process by using membranebased techniques might represent a remarkable improvement.