Acid recovery using diffusion dialysis with poly(4-vinylpyridine)-filled microporous membranes

Two series of membranes have been produced by photoinitiated polymerization of 4-vinylpyridine (4VP) and divinylbenzene (DVB) within the pores of polypropylene microfiltration membranes. The first series was comprised of membranes with varying mass gain and constant DVB content. The second series of membranes had similar mass gains but varying DVB content. The membranes were tested by diffusion dialysis of acid/salt solutions (HCl/NaCl/MgCl2) in order to determine the effects of both mass gain and degree of crosslinking on dialysis coefficients and acid/salt separation. It was found for the first series of membranes that the dialysis coefficients of the acid and salts decreased and then leveled off with increasing mass gain while separation increased and then also leveled off. The second series of membranes showed a decrease in acid and salt dialysis coefficients but a dramatic increase in separation as the DVB content was increased. These results are interpreted in terms of the fixed charge concentration and the water content of the membranes. A comparison is made with a commercial diffusion dialysis membrane.