This research discusses the separation of methane gas from three different gas mixtures, CH4/H2S, CH4/N-2 and CH4/CO2, using a modified silicon carbide nanosheet (SiCNS) membrane using both molecular dynamics (MD) and computational fluid dynamics (CFD) methods. The research examines the effects of different structures of the SiCNSs on the separation of these gas mixtures. Various parameters including the potential of the mean force, separation factor, permeation rate, selectivity and diffusivity arc discussed in detail. Our MD simulations showed that the separation of CH4/N-2 and CH4/CO2 mixtures was successful, while simulation demonstrated a poor result for the CH4/N-2 mixture. The effect of temperature on the diffusivity of gas is also discussed, and a correlation is introduced for diffusivity as a function of temperature. The evaluated value for diffusivity is then used in the CFD method to investigate the permeation rate of gas mixtures. (C) 2019 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.