COMPUTER-SIMULATION STUDIES OF THE STORAGE OF METHANE IN MICROPOROUS CARBONS

Simulated isotherm and energies of adsorption are reported for methane in a number of model porous solids at 300 K. The solids are made up of graphite basal planes arranged to make either parallel-walled slit pores or pores of triangular cross section. The limiting low coverage behavior was characterized by direct calculations of Henry's law constants and average gas-solid energies for the pore systems considered. The isotherms were evaluated for pressures ranging up to 50 atm by utilizing the Widom particle insertion algorithm. The simulations and calculations were carried out for a range of pore sizes and, in the case of the triangular cross-section, for a range of apex angles in the isosceles triangles considered. Methane storage capacities of model solids were evaluated for values of the porosity based on two different choices of pore wall thickness. Although it is shown that adsorption is not limited to monolayer formation under these conditions, capacities obtained are not sufficiently large to meet or exceed the commonly stated requirements for use in automotive fuel storage.