We use molecular dynamics simulations to analyze the dynamic behavior of the CO2/N-2 and CO2/CH4 gas mixtures through IRMOF-1 and Cu-BTC metal-organic frameworks-based membranes. Two approaches are considered to simulate the membrane system: permeation at constant pressure gradient and permeation at variable pressure gradient. The results show that both materials would work similarly to separate CO2/N-2 and that Cu-BTC is the most acceptable to separate CO2/CH4 gas mixtures. The roles of diffusion and adsorption are clearly elucidated from the simulations. These simulation results also demonstrate how metal-organic framework properties influence the separation ability of the membrane and help to understand the dynamic mechanism of the process at a molecular level thus providing orientations that may guide experimental work. (C) 2012 Elsevier B.V. All rights reserved.