Removal of greenhouse gases from gas streams using porous membranes was carried out in this work. Theoretical studies were performed in terms of mathematical modeling and numerical simulation of CO2 capture in a flat-sheet membrane contactor. Numerical simulation was performed using computational fluid dynamics (CFD) of mass and momentum transfer in the membrane module for laminar flow conditions. Physical absorption was considered in the simulations for absorption of CO2 in pure water. CO2 concentration distribution in the membrane module was determined through numerical solution of continuity equation coupled with the Navier-Stokes equations. The modeling predictions indicated that the CO2 concentration difference is not appreciable in the membrane direction. Moreover, velocity distribution was determined in the liquid side of membrane contactor. CFD also represents a design and optimization tool for membrane gas separation processes. POLYM. ENG. SCI., 55:975-980, 2015. (c) 2014 Society of Plastics Engineers