Adsorption and separation of hydrogen isotopes in carbon nanotubes: Multicomponent grand canonical Monte Carlo simulations

Adsorption isotherms of hydrogen isotopes from molecular simulations in carbon nanotubes and interstices are presented. The adsorption of pure isotopes follows Henry's law up to moderate coverages. A modified path integral grand canonical Monte Carlo (PI-GCMC) technique for mixture adsorption is presented and applied to adsorption of isotope mixtures in carbon nanotubes. Adsorption isotherms of H-2-T-2 mixtures in nanotubes and interstices are determined at 20 and 77 K. Selectivities for T-2 over H-2 are calculated over a range of pressures. Selectivity in the nanotubes and interstices increases with pressure until the nanotube is saturated. Comparison of simulation results with predictions based on ideal adsorbed solution theory (IAST) shows good agreement up to moderate loadings. At higher loadings, selectivities determined from multicomponent simulations remain roughly constant, whereas IAST predicts continued increase in selectivities. Isotherms for H-2-D-2 and the selectivities of D-2 over H-2 are determined for adsorption in (10,10) nanotubes and in the interstitial channels of closed (10,10) nanotubes. (C) 2002 American Institute of Physics.