A theoretical model simulating gas mixture separation using a composite inorganic membrane for high temperatures (T > 400 degrees C) is proposed. This model simulates operation of membrane described as three layers: metal, metal-support and support. The intermediate layer is considered to take into account the part of support with a few amounts of metal where the pore diameter is reduced due to the deposited metal on the wall of the pores. The computational fluid dynamics (CFD) approach is used. The simulation is based on the numerical solution of the three-dimensional (3D) Navier-Stokes equations coupled with the species governing equations on the three dimensional domain representing quite closely the selected module geometry. The permeability fluxes are calculated at different temperature and transmembrane pressures and compared with the experimental data. The simulation predictions show fairly good agreement with the measured permeation data. (C) 2014 Elsevier Ltd. All rights reserved.