Porous Silica-Zirconia(50%) Membranes for Pervaporation of iso-Propyl Alcohol(IPA)/Water Mixtures.

Porous silica-zirconia (ZrO2: 50 mol%) membranes of pore size around 0.5 nm were prepared by the sol-gel methods for separation of IPA/water mixtures by pervaporation. The prepared membranes showed a long time dependency in separation performance for about 30 hours before their steady states were attained. The IPA flux decreased gradually down to less than 1 mol·m–2h–1, while the water flux was nearly constant (about 300 mol·m–2h–1) at 73 mol% of IPA (10 wt% of water) in the feed mixture at 75°C, resulting in a drastic increase of separation factor from around 40 to 2500. The membranes also showed a high stability even at high water concentration (60 mol% of water) at 75°C, where the water flux exceeded 800 mol·m–2h–1.The time dependency of the separation performance is probably due to the formation of -OH groups on the pore surface and the succeeding adsorption and/or the reaction of IPA molecules which can reduce the effective pore diameter.