Co-adsorption of N2in the presence of CH4within carbon nanospaces: evidence from molecular simulations

Molecular simulations were performed to study the separation of CH(4) and N(2) from mixtures of composition x(CH(4))/x(N(2)) = 5/95 and x(CH(4))/x(N(2)) = 10/90 at 50 bar and 298 K on prototype carbon materials with different pore structures. The studied carbon structures include a slit and a tubular pore, that represent the simplest form of activated carbon and carbon nanotubes, respectively, in addition to a realistic porous carbon model with disordered pore structure and a recently introduced carbon foam model, which has a three-dimensional pore structure. The results indicate that, depending on the pressure and composition, the pore structure influences both the CH(4)/N(2) selectivity and the adsorption behaviour of the fluid molecules. The selectivity was decided by the interactions between CH(4) and N(2) molecules within the pore structure, in addition to the solid-fluid interactions. The simulation results indicate that, at least for the case of activated carbons (slit and random pores), it would not be appropriate to predict the binary adsorption behaviour of methane and nitrogen by means of pure component information. Regardless of the pore structure, the simulation results indicate that carbon materials show a CH(4)/N(2) (thermodynamic) selectivity of only 2-3 up to 2 bar at 298 K, and above this pressure, at equilibrium, none of the carbon materials is adequate for the efficient separation of this mixture.