Ultrathin self-assembled polyelectrolyte membranes for pervaporation

Ethanol-water pervaporation through new composite membranes with ultrathin self-assembled polyelectrolyte separating layer is described. The composite membranes were prepared by alternating electrostatic adsorption of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate sodium salt) (PSS) on a porous PAN/PET supporting membrane (a polyethylene terephthalate fleece coated with a thin layer of polyacrylonitrile). The sealing of the pores of the supporting membrane was studied by gas flow measurements. Pervaporation experiments were carried out under variation of the preparation and operation conditions. Generally it was found that the separation capability considerably increased, when the composite membrane was annealed at temperatures above 60 degrees C, while the flux simultaneously decreased. The same was found, when the number of PAH/PSS layers was increased. Raising the pervaporation temperature led to both an increase of the flux and the separation factor. The highest separation factor of 70 was found at a low water content of the feed of 6.2% (w/w). The corresponding flux was 230 g m(-2) h(-1). Pervaporation was feasible up to a water content of 24% (w/w) in the feed. At higher values, hydrolysis set in resulting in partial desorption of the separating layer. (C) 1998 Elsevier Science B.V. All rights reserved.