Membrane separation processes are attractive for the removal of carbon dioxide from natural gas since they consume less energy than conventional methods such as amine absorption and pressure swing adsorption. In this work inorganic-organic hybrid membranes were prepared employing chemical vapor deposition (CVD) of tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES) as silica and amino-silica precursors. They were deposited on the surface of a porous alumina support at high temperature using oxygen as a co-reagent. The objective was to enhance the permeance of CO2 by placing amine groups on the surface of the membrane. The APTES/(TE0S+APTES) ratio R was varied from 0% to 10000 in order to find an optimum composition for the separation of the CO2 from CH4. The best membrane was found to have a ratio R of 20% with a CO2 permeance of 2.3 x 10(-7) mol m(-2) s(-1) Pa-1 and an ideal CO2/CH4 selectivity of 40 at 393 K and 0.10 MPa of partial pressure difference. The transport mechanism for CO2 permeation was surface diffusion and for CH4 passage was gastranslation. The pore size of the membrane was evaluated by Tsuru`s method revealing a pore size of 0.44 nm. The results are significant because the permeance level is above that necessary for commercial use, the selectivity is adequate to produce a pipeline quality natural gas (purity > 2.4%), and the permeating gas is CO2 which allows retention of methane at high pressure. (C) 2014 Elsevier B.V. All rights reserved.