To inhibit the swelling of PVA membranes in aqueous alcohol solutions, which leads to lowered water permselectivity during separation, organic−inorganic hybrid membranes composed of poly(vinyl alcohol) (PVA) and tetraethoxysilane (TEOS) were prepared. When an aqueous solution of 85 wt % ethanol was permeated through the PVA/TEOS hybrid membranes during pervaporation, the separation factor for water permselectivity increased, but the permeation rate decreased, with increasing TEOS content. We concluded that the decreased permeation rate was caused by decreasing the degree of swelling of the membrane. Therefore, this decrease in the degree of swelling and the increase in membrane density were due to the formation of hydrogen bonds between the silanol groups resulting from the hydrolysis of TEOS and the hydroxyl group of PVA. When the PVA and PVA/TEOS hybrid membranes were annealed, the separation factor of these membranes increased with increasing annealing temperature and time. The fact that annealing at higher temperatures promoted the dehydration−condensation reaction between PVA and TEOS in PVA/TEOS membranes was related to the enhanced permselectivity of the PVA/TEOS membranes.

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.