Pervaporation characteristics of organic-inorganic hybrid membranes composed of poly(vinyl alcohol-co-acrylic acid) and tetraethoxysilane for water/ethanol separation

Swelling of poly(vinyl alcohol-co-acrylic acid) (P(VA-co-AA)) membranes in aqueous alcohol solutions operated under pervaporation conditions leads to low water/ethanol selectivity. To reduce swelling, organic-inorganic hybrid membranes composed of P(VA-co-AA) and tetraethoxysilane (TEOS) were prepared. However, when an aqueous ethanol solution was permeated through the P(VA-co-AA)/ TEOS hybrid membranes by pervaporation, the permeation rate increased and the water/ethanol selectivity decreased with increasing TEOS content. The increase in the permeation rate and the decrease in the water/ethanol selectivity were caused by an increase in the degree of swelling of the membrane and a decrease in the membrane density with increasing TEOS content. These effects resulted from insufficient formation of hydrogen bonds between the silanol groups by hydrolysis of TEOS and the hydroxyl and carboxyl groups of P(VA-co-AA). When the P(VA-co-AA)/TEOS hybrid membranes were annealed, the water/ethanol separation factor increased with increasing annealing time and TEOS content. Longer annealing time promoted the dehydration-condensation reaction between P(VA-co-AA) and TEOS in P(VA-co-AA)/TEOS hybrid membranes, leading to enhanced water/ethanol selectivity of the hybrid membranes.