Effect of Pore Morphology on the Adsorption of Methane/Hydrogen Mixtures on Carbon Micropores

The effect of pore structure and geometry on the selectivity of carbon materials for the adsorption of methane from a mixture of methane and hydrogen at 50 bar and 298 K was studied using a grand canonical Monte Carlo (GCMC) simulation technique. Hydrogen and methane were modeled by classical (nonquantum) Lennard-Jones intermolecular potentials. The pore morphologies studied included slits, nanotubes, a random porous structure, and a foamlike structure. The GCMC results show that both the pore size distribution and pore structure have significant effects on the selective adsorption of methane molecules from CH4/H2 mixtures. The selectivity depends on both energetic and packing effects. Pores that can accommodate either one or two layers of methane molecules give the optimum pore width for the separation of methane molecules. In the pressure range studied, of the four pore structures considered, nanotubes were found to have the highest selectivity (in the range of 15–51) toward the separation of methane molecules, followed by open structured foams (6–14), slits (6.6–16), and dense random structures (4.2–5.3). Prediction of the adsorption behavior of these mixtures by means of pure-component information seems to be inadequate for the very confined geometries.