Control of Antisolvent Mass Transfer through Porous Membranes for the Crystallization of Organic Compounds

Abstract

Crystallization faces great challenges from the point of view of technology readiness, process economics, and energy consumption. Membranes are capable of controlling both energy and mass transfer, and they can lead to major improvements if integrated into antisolvent crystallization processes, for example, limiting unfavorable kinetics and thermodynamics that are responsible for undesired crystal size and shape. In this work, membrane-assisted antisolvent crystallization (MAAC) was used to crystallize the amino acid l-serine. Two commercial membranes made of polyvinylidene fluoride and polypropylene with water contact angles of 130° and 150°, respectively, allowed a controlled antisolvent crystallization. These membranes controlled the transmembrane mass transfer of antisolvent (ethanol) under different feed and antisolvent velocities at ambient conditions. In all cases, a narrow crystal size distribution of l-serine was obtained reflected in a coefficient of variation (CV) of 31–37%, compared with batch antisolvent crystallization or drop-by-drop crystallization where the CV was 63 and 54%, respectively. Thanks to the measurement of l-serine and ethanol concentration along the operating time, the mass transfer coefficient of MAAC was evaluated. Increasing the antisolvent or the crystallizing solution velocity showed that a too high value of one or the other could result in wetting or system blockage (inside the membrane contactor, module, or tubing). This study explains the transmembrane mass transfer in MAAC and the resulting crystal properties.