Simulations were made on the permeation of pure and mixed gases across carbon membranes having three different pore shapes: diamond path, zig-zag path and straight path, composed of micro-graphite crystallites. The smallest pore width of the membranes was set at 0.5nm and methane and ethane, whose molecular size in the shortest diameter was 0.37 to 0.38nm, were chosen as permeating gases. The density profiles of methane and ethane showed that the permeation resistance inside the diamond path and zig-zag path membranes was significant while the resistance of the straight path membrane was localized at the membrane exit. In the case of mixed-gas permeation, the permoselectivities of ethane to methane were larger than the ideal separation factors for the three membranes due to the competitive adsorption of ethane which was a strongly adsorbed component. However, the permoselectivities were smaller than the adsorption equilibrium separation factors since the higher permeation resistance of ethane played a counteractive role.

Non-Equilibrium Molecular Dynamics Simulation Studies on Gas Permeation Across Carbon Membranes with Different Pore Shape Composed of Micro-Graphite Crystallites. Furukawa, S.I., Nitta, T.: Journal of Membrane Science, 2000, 178[1-2], 107-19