Stability and performance of porous silica-zirconia composite membranes for pervaporation of aqueous organic solutions

Porous silica-zirconia membranes were fabricated by the sol-gel techniques to study their stability against water and the pervaporation performance of aqueous solutions of organic solvents. Zirconia (10-70mol%) was added to silica to obtain silica-zirconia composite membranes by firing at 400-500 degreesC for pervaporation tests with organic solvent/water mixtures, such as iso-propyl alcohol (IPA)/water and tetrahydrofuran (THF)/water mixtures at their normal boiling points. The membrane coatings have been done effectively by the hot-coating methods proposed previously. Boiling water treatments introduced in the coating processes have made the membranes quite stable even in the high water concentration region of aqueous organic solutions at their normal boiling points. Zirconia contents larger than about 40 mol% have made the silica-zirconia membranes quite stable. The membranes of zirconia contents less than about 30 mol% were found not stable in a dilute aqueous solution of IPA. The membranes fabricated by the conventional dip-coating methods with slow drying were not stable against water because of the probable segregation of silica and/or silica-rich phases during drying. The membranes fired at lower temperature (400 C) gave a higher water flux of around 500 mol m(-2) h(-1) (9kg m(-2) h(-1)) with a separation factor larger than 1500 at 10 wt.% of water in the boiling feed of IPA/water mixture, for example. (C) 2002 Elsevier Science B.V. All rights reserved.