Silica-zirconia (SZ, molar ratio 9/1) membranes, the pore size of which were adjusted in a range of approximately 13 1-3 nm, were prepared by the sol-gel process. Several of these membranes were modified via a gas-phase reaction with trimethylchlorosilane (TMS) at 200 degreesC. Various types of pure solvents were permeated at temperatures in the range of 20-60 degreesC. The collected data shows that the transport mechanism through the unmodified membranes does not obey the viscous flow mechanism, since pure solvent permeabilities multiplied by the viscosity, L(p)mu, which should be constant for the case of the viscous-flow mechanism, increased with temperature. On the other hand, SZ membranes modified with TMS showed a relatively constant L(p)mu, suggesting that the viscous flow mechanism holds. The nanofiltration of ethanol solutions with alkanes (hexane, decane, tetradecane) and alcohols (hexanol, octanol, decanol) as solutes was investigated. An SZ membrane having an average pore size of 1 nm showed a molecular weigh cut-off of approximately 200 and an approximate permeate flux of 3 kg m(-2) h(-1) at 60 degreesC under an applied pressure of 30 bar. Rejections of alkanes were almost constant irrespective of temperatures, while those of alcohols decreased with temperature. (C) 2003 Elsevier Science B.V. All rights reserved.