甲烷在官能团化石墨中吸附行为的影响因素研究

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

页岩中干酪根结构简化为不同碳氧比石墨结构,利用巨正则蒙特卡罗模拟方法研究甲烷分子在不同碳氧比石墨中吸附行为,讨论了孔径、温度、含水量和二氧化碳对甲烷在不同碳氧比石墨中吸附行为的影响,在此基础上分析碳氧比变化对甲烷吸附行为影响,揭示了甲烷在不同碳氧比石墨中的微观吸附机理以及温度、水分及二氧化碳对甲烷吸附行为的影响及其微观作用机理.研究结果表明:相同碳氧比中,当孔径从1nm增大到20nm时,甲烷在碳氧比为4孔中的平均等量吸附热从19.65kJ/mol减小为7.88kJ/mol,且甲烷过剩吸附量随微孔孔径增大而增大,而随中孔孔径增大而减小;相同孔径中,当碳氧比从4增加到20时,甲烷在孔径1nm中的平均等量吸附热从19.65kJ/mol减小为16.39kJ/mol,且甲烷过剩吸附量随着碳氧比增大而减小;当温度从313K升高到373K时,甲烷在碳氧比为4孔中的吸附逐渐由能量较低的吸附位向能量较高的吸附位转移,甲烷等量吸附热从12.76kJ/mol减小为12.16kJ/mol,造成甲烷过剩吸附量降低;水分子在孔中受到范德华力和静电能共同作用使其聚集在含氧官能团附近,且水分子占据了甲烷分子吸附空间,造成甲烷过剩吸附量降低;在多元组分竞争吸附中,不同碳氧比石墨对二氧化碳的吸附能力大于甲烷.甲烷在气相中摩尔分数降低、甲烷吸附位的变化以及甲烷吸附空间减小将导致了甲烷吸附能力降低.

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 1nm to 20 nm,the isosteric heat of the methane in C4 pore decreases from 19.65kJ/mol to 7.88kJ/mol,and the excess adsorption quanti-ty 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 4to 20,the isosteric heat of methane in pores of 1nm falls from 19.65kJ/mol to 16.39kJ/mol,and the excess adsorption quantity decreases with the increase of the C/O.When the temperature increases from 313Kto373 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 12.76kJ/mol to 12.16kJ/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.