Roles of the Porosity and Surface Oxygen Groups on the Adsorption of Methane on Coals

One bituminous coal was modified with H2O2, (NH4)(2)S2O8 and HNO3 respectively, to prepare coal samples with different surface properties. The oxygen groups on coal surface were characterized by X-ray photoelectron spectroscopy (XPS). The textures of the coal samples were investigated by N-2 adsorption at 77 K. The methane adsorption behaviors of thecoal samples were measured at 303 K in pressure range of 0-5.3 MPa by a volumetric method. The methane adsorption datawere fitted to the Langmuir model. It was observed that there was, in general, a positive correlation between the methaneadsorption capacity and the S-BET of coals while a negative correlation between methane saturated adsorption capacity and the O-total/C-total. The methane adsorption capacity was determined by the coal surface chemistry when the microporosity parameters of two samples were similar. Coal with a higher amount of oxygen surface groups, and consequently with a less hydrophobic character, had lower methane adsorption capacity.