Recently, purification of raw biogas has attracted a great attention of research community. Possibility of effective waste utilization for cheap biofuel production has enormous ecological and economical benefits. In this work a water-swollen thin film composite membrane for effective separation of carbon dioxide from methane in biogas is presented. The hydrophilic reverse osmosis membrane creates under water vapor condensing conditions a thin selective separation layer in which dissolved feed gaseous mixture, except methane. Water vapor saturated biogas was brought into a contact with cooled membrane in order to keep the selective skin layer. Sweeping gas N-2 is used to keep constant driving force and to control partial water evaporation from the membrane. Under the described experimental conditions was obtained retentate stream containing 95 vol.% of methane. (c) 2012 Elsevier B.V. All rights reserved.