Experimental and Theoretical Studies of Supercritical Methane Adsorption in the MIL-53(Al) Metal Organic Framework

The adsorption equilibrium properties of supercritical methane in the large-pore (lp) structure of the MIL-53(Al) metal organic framework were studies experimentally by gravimetric adsorption and theoretically by grand canonical Monte Carlo(GCMC)simulation The adsorption experiments span a broad range of pressures (0.01-7 MPa) and temperatures (303-353 K). In our Molecular simulation work, MIL-531p(Al) is assumed, to have a perfect, rigid lattice, and both fluid fluid and solid fluid interactions are modeled using the TraPPE-UA,74: force field. The adsorption isotherms and isosteric heats of adsorption predicted by GCMC simulation, without any reparametrization of the TraPPE-UA force field parameters, are in good agreement with the experimental measurements. Our molecular simulations predict that the amount of methane adsorbed in the porous framework of MIL-531p(Al) at 298.15 K and 3.5 MPa is 5.79 mol/kg, yielding a methane storage capacity of 132 6 v/v (volumes of stored gas, measured at conditions, per storage volume) for a monolithic block and 107.2 v/v for the theoretical limit of a close-packing of uniform spehrical particles. For an isothermal (298.15 K) discharge cycle between 3.5 and 0.136 MPa, the predicted net deliverable capacity is 114.0 (v/v)(net) for a monolith and 93.1 (v/v)(net) for a close-packed bed. If, however, the storage system is operated at 253 K, the net storage capacity of a monolithic block of MIL-53(Al) increases to a value that is very close to the DOE target of 150 (v/v)(net).