Tuning the acid recovery performance of poly(4-vinylpyridine)-filled membranes by the introduction of hydrophobic groups

Two series of anion-exchange membranes have been produced by photo-initiate d copolymerization of 4-vinylpyridine and divinylbenzene (DVB) within the p ores of polypropylene microfiltration membranes followed by quaternization of the pyridine nitrogen atoms. The membranes were tested fur use in acid r ecovery applications by performing diffusion dialysis of acid/salt solution s (HCl/NaCl/MgCl2) and determining dialysis coefficients and acid/salt sele ctivity. The nature of the water present in the membranes was examined by d ifferential scanning calorimetry (DSC). The first series was comprised of m embranes with varying DVB content and all were quaternized with a methyl gr oup. When compared to similar protonated membranes, this series showed a de crease in fixed charge concentration, an increase in dialysis coefficients, an increase in selectivity of HCl over NaCl and a slight decrease in selec tivity of HCl over MgCl2. The second series had different quaternizing grou ps. It was found for this series that increasing the size of the N-alkyl su bstituent resulted in an increase in the membrane fixed charge concentratio n, a decrease in dialysis coefficients and a dramatic increase in selectivi ty of acid over salts. The results are interpreted in terms of the effects of the hydrophobic alkyl groups on the water structure in the membranes. Th e acid recovery performance of the N-alkylated membranes was shown to be be tter than a commercial diffusion dialysis membrane. (C) 2001 Elsevier Scien ce B.V. All rights reserved.