Enhancing the permselectivity of pervaporation membrane by constructing the active layer through alternative self-assembly and spin-coating

Polyelectrolyte composite membranes with ultrathin active layer were utilized for pervaporation dehydration of ethanol aqueous solution. The active layer was constructed by sequential spin-coating and self-assembly of chitosan (CS) and hyaluronic acid (HA), respectively, on the polyacrylonitrile (PAN) support layer. The spin-coating layer was denoted as inner layer, and the self-assembly layer was denoted as capping layer, and these two layers were compatible well without distinct boundary. Compared with single-active-layer CS/PAN and HA/PAN membranes, the HA/CS/PAN membranes showed higher separation factor. It was also observed that the separation factor of the HA/CS/PAN membranes with HA as capping layer was higher than that of the CS/HA/PAN membrane with CS as capping layer, but their fluxes were quite close. A probable explanation was presented based on the higher sorption selectivity of HA and the higher diffusion selectivity of CS. Under the optimized membrane preparation recipe, the HA/CS/PAN membrane exhibited the permeation flux of 1447 g/(m2 h) and the separation factor of 704 for dehydration of 90 wt.% ethanol aqueous solution at 80 °C. Furthermore, the membranes displayed the desirable long-term operation stability.