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

Crystallizationfaces great challenges from the point of view oftechnology readiness, process economics, and energy consumption. Membranesare capable of controlling both energy and mass transfer, and theycan lead to major improvements if integrated into antisolvent crystallizationprocesses, for example, limiting unfavorable kinetics and thermodynamicsthat are responsible for undesired crystal size and shape. In thiswork, membrane-assisted antisolvent crystallization (MAAC) was usedto crystallize the amino acid l-serine. Two commercial membranesmade of polyvinylidene fluoride and polypropylene with water contactangles of 130 & DEG; and 150 & DEG;, respectively, allowed a controlledantisolvent crystallization. These membranes controlled the transmembranemass transfer of antisolvent (ethanol) under different feed and antisolventvelocities at ambient conditions. In all cases, a narrow crystal sizedistribution of l-serine was obtained reflected in a coefficientof variation (CV) of 31-37%, compared with batch antisolventcrystallization or drop-by-drop crystallization where the CV was 63and 54%, respectively. Thanks to the measurement of l-serineand ethanol concentration along the operating time, the mass transfercoefficient of MAAC was evaluated. Increasing the antisolvent or thecrystallizing solution velocity showed that a too high value of oneor the other could result in wetting or system blockage (inside themembrane contactor, module, or tubing). This study explains the transmembranemass transfer in MAAC and the resulting crystal properties. Membrane-assisted antisolvent crystallization(MAAC) isinvestigated through the evaluation of the transmembrane mass transfer,the evolution of supersaturation, and its impact on crystal size andsize distribution. l-Serine in water was chosen as the crystallizationsystem with ethanol as the antisolvent. Some potential challengesin MAAC operation were also addressed and their mitigation pathways.