High mechanical strength conductive inorganic–organic composite membranes for chiral separation and in situ cleaning

Abstract

Enantiomeric separation based on membrane techniques has the advantages of energy efficiency, sustainable operation, and no additives, but there are no commercially available chiral membranes. The main reasons restricting the development of chiral membranes are separation specificity, poor mechanical properties, and membrane fouling. Therefore, we developed a novel chiral membrane with a stainless steel mat mesh as the base and β-cyclodextrin blended in cellulose acetate as the functional layer. The organic layer was loaded on the inorganic base by nonsolvent-induced phase inversion, and the two post treatments were optimized. The results indicate that the optimal percent enantiomeric excess (ee%) was 96.98 ± 5.22 % for d,l-tryptophan, 46.38 ± 1.65 % for d,l-phenylalanine, 11.50 ± 2.52 % for (RS)-propranolol, and 5.16 ± 0.88 % for (RS)-warfarin. The mechanical properties of stainless steel chiral composite membranes are better than those of other chiral membranes, and the Young's modulus values reached 3234 MPa. In addition, ultrasonic cleaning and electrolytic cleaning were successfully tested to solve the membrane fouling problem, and a comparative study indicated that electrolytic cleaning has low energy consumption and is a fast and effective cleaning method that can achieve flux recovery. These results indicate that conductive chiral membranes can achieve long-term separation of chiral compounds and have great potential for industrial applications.