Membrane separation of CO2 from synthesis gas could be an energy efficient and simple alternative to other separation techniques. In this work, a membrane comprised of an about 0.7 mu m thick MFI film on a graded alumina support was used to separate CO2 from synthesis gas produced by pilot scale gasification of black liquor. The separation of CO2 from the synthesis gas was carried out at a feed pressure of 2.25 MPa, a permeate pressure of 0.3 MPa and room temperature. In the beginning of the experiment, when the H2S concentration in the feed was 0.5% and the concentration of water in the feed was 0.07%, a CO2/H-2 separation factor of 10.4 and a CO2 flux of 67.0 kg m(-2) h(-1) were observed. However, as the H2S concentration in the feed to the membrane increased to 1.7%, the CO2/H-2 separation factor and the CO2 flux decreased to 5 and 61.4 kg m(-2) h(-1), respectively. The results suggest that MFI membranes are promising candidates for the separation of CO2 from synthesis gas. (C) 2013 Elsevier B.V. All rights reserved.