Self-assembly of polyelectrolyte multilayer pervaporation membranes by a dynamic layer-by-layer technique on a hydrolyzed polyacrylonitrile ultrafiltration membrane

Abstract

This paper is concerned with the self-assembly of polyelectrolyte multilayer membranes (PEMMs) by using dynamic layer-by-layer (LBL) adsorption technique for pervaporation separation of water/alcohol mixtures. The polyacrylonitrile (PAN) ultrafiltration membrane used as a support was firstly hydrolyzed with alkaline solutions followed by alternatively depositing polyethyleneimine (PEI) and polyacrylic acid (PAA) under a pressure of 0.1 MPa. The PEI–ethanol solution and PEI-aqueous solution were used to investigate the effects of solvents on the assembly process. It was found that both separation factor and permeate flux were improved remarkably by replacing PEI aqueous solution with PEI–ethanol solution. Because only a few composite bilayers were needed to achieve a good capability in the dynamic LBL process, the hydrolysis degrees of PAN support membrane would strongly affect the pervaporation membrane performances. It was also noted that the exposure of membranes to low pH after hydrolysis would not benefit for the assembly. Further studies were conducted to investigate the effects of alkali species on the PAN hydrolysis and pervaporation performances of PEMMs. The contribution of alkali species on the pervaporation performance was in the order of KOH > NaOH > LiOH. Finally, the performances of PEI/PAA multilayer membranes assembled on the hydrolyzed PAN support were evaluated with a relatively wide range of feed temperature and concentration. The PEMMs obtained with only 2.5 bilayers had a separation factor of 604 and a permeate flux of 314 g/m 2 h (70 °C) for pervaporation of 95 wt% ethanol–water mixture.