A ZSM-5 membrane synthesized on a stainless steel porous tube was used for the separation of p-xylene from its isomers, m- and o-xylene. The membrane was prepared by secondary growth on the outer surface of the support. The permeation regime through the membrane was described by a combination of adsorption-diffusion steps. In order to examine the durability of the membrane, a sequence of three thermal cycles was conducted. N-2 permeation measurements together with scanning electron microscopy (SEM) observations were the tools used to detect whether or not cracks developed after exposure to the xylene isomers up to 400 degrees C. After 1000 h on stream, the membrane was selective to p-xylene, the N-2 permeance fluxes remained unchanged and the SEM micrographs did not reveal any discontinuity. (c) 2006 Elsevier B.V. All rights reserved.