CO_2/CH_4在干酪根中竞争吸附规律的分子模拟

Molecular simulation of CO_2/CH_4 competitive adsorption in kerogen

选取有机质作为研究对象,构建干酪根模型,采用巨正则系综蒙特卡罗(GCMC)方法和分子动力学方法(MD)研究不同摩尔分数、不同压力下CH_4和CO_2的气体的竞争吸附行为以及吸附引起的干酪根本体形变。结果表明:CH_4和CO_2单组分吸附时吸附量随着压力的增大而增大,CO_2吸附会在较小的压力时达到饱和,两种气体吸附符合Langmuir吸附规律,可以使用Langmuir方程进行拟合;在相同的压力和温度下,CO_2/CH_4吸附选择性会随着CO_2摩尔分数的增大而减小,CO_2更易被干酪根吸附;干酪根与CO_2有较强的相互作用,干酪根中不同的原子对吸附起着不同的作用;低压阶段吸附是引起体积应变的主要原因,高压阶段压力对体积应变发挥明显作用。

The kerogen model was built and the organic matter was selected as the research object. The CH4 and CO2 adsorp-tion behavior and the associated volumetric strain of the kerogen at different CO2 mole fractions and different pressures were investigated using Monte Carlo ( GCMC) and Molecular Dynamic methods. The results show that the adsorption amount of CH4 and CO2 increases with pressure increase. And CO2 adsorption amount can reach maximum at lower pressure. The ad-sorption of CH4 and CO2 accords with the law of Langmuir adsorption and can be fitted by Langmuir equation. The adsorption selectivity of CH4/CO2 decreases as the CO2 mole fractions increase at the same pressure and temperature, and the CO2 is easier adsorptive by kerogen. Also it is found that there is a strong interaction between kerogen and CO2 , and different atoms play different roles for adsorption in kerogen. At low pressures, the adsorption is the main reasons for volumetric strain, and at high pressures, the pressure is a significant role in volumetric strain.