Improving the stability of layer-by-layer self-assembled membranes for dehydration of alcohol and diol

In this study, polyelectrolyte membranes were prepared by layer-by-layer self-assembly on top of an interfacially polymerized polyamide substrate, and these thin-film-composite membranes were studied for pervaporative dehydration of ethylene glycol, ethanol and isopropanol. The composite membranes based on polyethylenimine/poly(acrylic acid) (PEI/PAA) complexes worked well for dehydration of ethylene glycol, but unsatisfactory for the dehydration of ethanol and isopropanol at relatively high feed alcohol concentrations, which was found to be caused by the stability issues of PEI/PAA bilayers and the polyamide substrate in the solvents. To improve the performance of the composite membranes for dehydration of ethanol and isopropanol, the outmost surface layer was deposited with PEI, followed by crosslinking. A further improvement in the membrane selectivity was accomplished by substituting the PEI with partially protonated chitosan in the last few polyelectrolyte bilayers during membrane fabrication. It was demonstrated that using interfacially polymerized polyamide membrane as a substrate, polyelectrolyte membranes with less than 8 bilayers can be fabricated for the dehydration of alcohol and diol.