Effect of pore structure on the selectivity of carbon materials for the separation of CO2/H2 mixtures: new insights from molecular simulation

Molecular simulations were performed to study the effect of the nanoporous structure on the selectivity of carbon materials for the adsorption of carbon dioxide from mixtures of carbon dioxide and hydrogen at 298 K and for fluid compositions: x(CO2)/x(H2) = 1/9 and 2/8. Both carbon dioxide and hydrogen were studied using classical Lennard-Jones intermolecular potentials. Typical pore geometries such as slit-shaped pores and nanotubes were considered, along with a hypothetical foam-like structure and a carbon model exhibiting a random porous structure with a wide pore size distribution. Simulation results show that selectivity for carbon dioxide is sensitive to pore structure and composition; the solid/fluid interactions play a decisive role in the selectivity and most of the effects can be explained by the independent analysis of the interactions of carbon dioxide with the pore walls. In the range of pressure and composition studied, nanotubes have the highest selectivity towards carbon dioxide (100-313), followed by slit (9-63), foam-like (29-35) and random porous carbon (8-30). Molecular simulations further indicate that predicting the adsorption behavior for a CO2/H-2 mixture from pure component isotherms is inadequate due, to the competing effects of the molecules with the pore walls.