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Antisolvent crystallization is indispensable for the crystallization of heat-sensitive compounds from solutions. However, such crystallization happens instantly, and supersaturation is difficult to control, resulting in non-uniform crystal morphology and size. Membrane-assisted antisolvent crystallization (MAAC) can control the mass transfer of the antisolvent into the solution and mixing, plus being a substrate for heterogeneous crystallization. This work investigates the optimum conditions to operate MAAC and attempts to understand the different interactions between the membrane and the solute-solvent-antisolvent system through molecular dynamics (MD) simulations. Ongoing research on MAAC covered the use of Polyvinylidene fluoride (PVDF) and Polypropylene (PP) membranes for the crystallization of glycine in water, using ethanol as antisolvent (Fig. 1). Results demonstrated that an optimized operation of MAAC dictates a proper description of the mass transfer. The stability of the mass transfer coefficient is crucial to ensure no membrane wetting by the crystallizing solution and controlled transport of the antisolvent. Second, a specific combination of the operating conditions, such as flow rate, antisolvent composition, temperature, or gravity resistance plays a key role in tailoring the induction time that correlates directly with crystal formation kinetics. Finally, fine-tuning the properties of the membrane, such as its porosity, thickness, and hydrophobicity, is advantageous to control supersaturation further and assert a reproducible production of crystals with a narrow crystal size distribution (CSD) [1-3]. MD simulations of crystallization models of glycine-water and glycine-water-ethanol mixtures, built at supersaturation showed a difference in the organization of glycine molecules owing to the mutual diffusion behavior where the antisolvent diffuses faster into the solvent or vice versa (Fig. 2). Membranes control of supersaturation and crystal properties has potential in intensifying crystallization processes necessary for different applications such as control of polymorphism, reaction purification, and crystal size control.
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Chergaoui, S., Tocci, E., Debecker, D., Leyssens, T., & Luis Alconero, P. (2023). The role of membranes in controlling supersaturation of antisolvent crystallization: Empirical and MD studies. ITM Seminar Day, Rende, Italy. https://hdl.handle.net/2078.5/100726