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

► Composite membranes were prepared by sequential spin-coating and self-assembly. ► Positioning of HA layer and CS layer in membrane affected the separation factor. ► HA/CS/PAN membrane showed both high permeability and selectivity. 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/(m 2 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.