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. Th e polymer was ion-exchanged with quaternary ammonium cations having aliphat ic substituents of various chain lengths. The pervaporation of aqueous n-bu tanol solutions using these membranes gave a permeate more concentrated in n-butanol; therefore, they were alcohol-selective. The separation factor in creased and the permeate flux decreased as the chain lengths of the aliphat ic substituents were increased. Hence, the mass-transport properties of suc h membranes can be controlled or altered to yield some desired permselectiv ity 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 memb ranes and its effect on membrane performance was investigated as well. As t he n-butanol content was increased, the swelling of the membranes increased greatly. High membrane swelling caused a reduction in the separation facto r. (C) 1999 John Wiley & Sons, Inc.