Polyelectrolyte multilayer membranes for pervaporation separation of alcohol/water mixtures

Composite membranes with ultrathin polyelectrolyte separation layer were studied on their use for alcohol/water separation under pervaporation conditions. The separating layer was prepared by alternate electrostatic layer-by-layer adsorption of cationic and anionic polyelectrolytes onto a porous polymer support. Alcohol/water pervaporation led to water enrichment in the permeate, which was highest for polyelectrolytes of high charge density such as polyvinylamine (PVA), polyethyleneimine (PEI) and polyvinylsulfate (PVS), and if the preparation conditions of the separation layer (pH, ionic strength of polyelectrolyte solutions) were properly chosen. If a PVA/PVS separation layer was used for ethanol/water pervaporation, a separation factor α up to 700 was found, while the flux was about 0.5 kg m−2 h−1. For 1-propanol/water and t-butanol/water pervaporation, the α-values were up to 7×103 and 3.2×104, respectively.