MCM-22 membranes were prepared on a porous alpha-alumina tube using a secondary growth technique consisting of the deposition of seed crystals on a substrate followed by crystal growth under hydrothermal conditions. In this study, two types of seed crystals. MCM-22 and ITQ-2, were used. The MCM-22 membrane prepared using ITQ-2 seed crystals (MCM-22 (I) membrane) was composed of MCM-22 poly-crystals with a thickness of 5 mu m, which is much thinner than that of the MCM-22 membrane prepared using MCM-22 seed crystals (MCM-22 (M) membrane) (15-20 mu m). Vapor permeation of water/acetic acid mixtures through the MCM-22 membranes was studied. The MCM-22 (I) membranes calcined at 400 degrees C showed a high separation factor of 78 with a water permeance of 4 x 10(-8) mol m(-2) s(-1) Pa(-1) at 120 degrees C. Elevating the calcination temperature to 500 degrees C resulted in a lower separation factor. The MCM-22 (I) membrane calcined at 400 degrees C has a hydrophilic internal surface due to the presence of silanol groups within the framework that contribute to the high selectivity to water permeation. (C) 2011 Elsevier B.V. All rights reserved.