Selectivity and self-diffusion of CO(2) and H(2) in a mixture on a graphite surface

We performed classical molecular dynamics (MD) simulations to understand the mechanism of adsorption from a gas mixture of CO(2) and H(2) (mole fraction of CO(2) = 0.30) and diffusion along a graphite surface, with the aim to help enrich industrial off-gases in CO(2), separating out H(2). The temperature of the system in the simulation covered typical industrial conditions for off-gas treatment (250–550 K). The interaction energy of single molecules CO(2) or H(2) on graphite surface was calculated with classical force fields (FFs) and with Density Functional Theory (DFT). The results were in good agreement. The binding energy of CO(2) on graphite surface is three times larger than that of H(2). At lower temperatures, the selectivity of CO(2) over H(2) is five times larger than at higher temperatures. The position of the dividing surface was used to explain how the adsorption varies with pore size. In the temperature range studied, the self-diffusion coefficient of CO(2) is always smaller than of H(2). The temperature variation of the selectivities and the self-diffusion coefficient imply that the carbon molecular sieve membrane can be used for gas enrichment of CO(2).