Isomorphously substituted Sn-ZSM-5 zeolite membranes supported on porous alpha-Al2O3 tube was first prepared for pervaporation separation of acetic acid/water mixture by in situ hydrothermal synthesis from a clear solution. XRD, IR analysis confirms the incorporation of Sn atom into MFI framework. The Sn-ZSM-5 membranes obtained were more effective for separation of acetic acid from water than the silicalite-1 membrane. The effects of Si/Sn ratio in the synthesis solution, feed concentration and temperature on separation performance of the obtained Sn-ZSM-5 membranes were examined. Separation factor for Sn-ZSM-5 membranes increased with decreasing Si/Sn ratio from infinity to 25 while the total flux decreased. Both the total fluxes and separation selectivity decreased with increasing feed acetic acid concentration in the range from 2 to 28 wt%. Separation factor increased as temperature increased from 303 to 363 K. The Sn-ZSM-5 membrane with Si/Sn ratio of 25 had separation factor of 7.7 with a total flux of 0.49 kg/m(2) h for a 5 wt% acetic acid aqueous solution at 363 K. It is indicated that the incorporation of Sn atom into MFI framework enhanced the hydrophobicity of MFI membrane and improved separation selectivity for acetic acid. (C) 2009 Elsevier B.V. All rights reserved.