Investigation on the influence factors of the methane adsorption in functionalized graphite

XIONG Jian; LIU Xiangjun; LIANG Lixi

Abstract：In this article,the kerogen in shales was simplified into graphite with different carbon to oxygen ratio(C/O).The adsorption mechanism of methane in the graphite with different C/O were investigated by the Grand Canonical Monte Carlo simulations,and the effects of pore sizes,temperatures,water contents and carbon dioxide on the methane adsorption in graphite with different C/O were discussed.On this basis,the variation of C/O on the methane adsorption were studied.The microcosmic adsorption mechanism of methane in graphite with different C/O,and the influences of temperature,water and carbon dioxide on the methane adsorption as well as their interaction mechanism were also revealed.The results show that with the same C/O,when the pore size increases from 1 nm to 20 nm,the isosteric heat of the methane in C4 pore decreases from 19.65 kJ/mol to 7.88 kJ/mol,and the excess adsorption quantity grows with the increase of micropore size,but decreases with the increase of mesopore size.With the same pore size,when the value of C/O increases from 4 to 20,the isosteric heat of methane in pores of 1 nm falls from 19.65 kJ/mol to 16.39 kJ/mol,and the excess adsorption quantity decreases with the increase of the C/O.When the temperature increases from 313 K to 373 K,the adsorption of methane in C4 pore transfers from the lower energy adsorption sites to the higher ones and the isosteric heat of methane decreases from 12.76 kJ/mol to 12.16 kJ/mol,resulting in the decline of excess adsorption quantity.Jointly affected by the van der Waals force and Coulomb force,the water molecules in the pore gather around the oxygen-containing functional group and occupy the methane adsorption space,which also leads to the decrease of the excess adsorption quantity.In the multi-component competitive adsorption,graphite with different C/O has stronger adsorption capacity for carbon dioxide than methane.In general,the decline of mole fraction in the gas phase,the changes of adsorption site and the reduction of the adsorption space would all cut down the methane adsorption capacity.