Water–ethanol permseparation by pervaporation through the plasma graft copolymeric membranes of acrylic acid and acrylamide

Abstract

Acrylic acid was copolymerized with acrylamide onto the porous polypropylene film which had been previously treated by glow discharge plasma, and the partially ionized membranes were prepared with treating in dilute sodium hydroxide aqueous solution. Using these membranes with different ratios of polyacrylate ion, water–ethanol permseparation was investigated. The membranes were water-permselective because of the hydrophilicity, and the permselectivity was increased by ionization generally for the feeds with ethanol concentration more than 50%. In the lower ethanol concentration range, the permselectivity was not so good because of the much higher permeation rate. When the permselectivity was evaluated by the products of separation factor (a) and Flux (Q), the copolymerized membranes with the acrylic acid mixing at 0.4 were superior to the ion-exchange membranes, although somewhat inferior to the ionized membranes of acrylic acid grafting which had been attempted previously. In the ionized membrane of the copolymer, the activation energy for permeation lied between 4.2 and 5.5 kcal/mol, and was much smaller than that of the neutral membranes before ionization; i.e., the decrease of flux was depressed even at the lower temperature.