Removal of n-butanol from aqueous solutions by ion-exchange membranes containing organic counterions

The pervaporation of aqueous butanol solutions was investigated using thin-film composite membranes composed of a poly(vinylidene fluoride) substrate coated with a sulfonated poly(2,6-dimethyl-1,4-phenelene oxide) polymer. The polymer was ion-exchanged with quaternary ammonium cations having aliphatic substituents of various chain lengths. The pervaporation of aqueous n-butanol solutions using these membranes gave a permeate more concentrated in n-butanol; therefore, they were alcohol-selective. The separation factor increased and the permeate flux decreased as the chain lengths of the aliphatic substituents were increased. Hence, the mass-transport properties of such membranes can be controlled or altered to yield some desired permselectivity by the introduction of a proper counterion. It was observed that the n-butanol flux was small relative to the total flux and, therefore, the water flux dominated the total permeate flux. The degree of swelling of the membranes and its effect on membrane performance was investigated as well. As the n-butanol content was increased, the swelling of the membranes increased greatly. High membrane swelling caused a reduction in the separation factor. (C) 1999 John Wiley & Sons, Inc.