Process intensification of antisolvent crystallizers using polymeric membranes : controlling antisolvent crystallization kinetics via tuning membrane characteristics

Crystallization process is complex yet essential for numerous chemically-related and engineering fields. Mastering this operation contributes to carbon capture and utilization, purify water, recover high-value compounds, produce vital drugs or run batteries. Conventional crystallizers still rely heavily on cooling which can be highly energy consuming and degrade the quality of the crystals. Membrane technologies have shown potential on controlling the rate of supersaturation through precise mass transfer and allowing heterogeneous nucleation on their active surface. In 2015, initial work on the benefits of Membrane-Assisted Antisolvent Crystallization (MAAC) as an alternative to conventional crystallizers emerged and heralded bright days for this technique. However, the impact of membrane characteristics on crystallization is still unclear from existing studies. This work focuses on the impact of membrane characteristics, namely thickness, porosity, and hydrophobicity, on MAAC process. For this purpose, several PVDF membranes were synthesized using non-solvent induced phase separation (NIPS) with various characteristics, and were tested. The results were reported via: (1) the investigation of the membrane and crystal morphology using SEM imaging, (2) the quantitative evaluation of mass transfer and supersaturation to understand the effect of kinetics and thermodynamics variable on the crystal purity defined by XRD and granulometry analyses. The thinner, more porous or least hydrophobic a membrane was, the more antisolvent transmembrane flux and mass transfer were promoted. This results in an increase of the supersaturation rate, favoring the nucleation step over crystal growth and thus producing narrow crystal size distribution and tunable crystal size. Nevertheless, hydrophobicity promotes the phenomenon of heterogeneous nucleation achievable at a lower degree of supersaturation. In all, membranes can combine characteristics to implement the best operating conditions for any antisolvent crystallization process. This work provided a preliminary understanding for the impact of essential membrane characteristics on crystallization; hence motivates further studies in this direction.