CO_2和CH_4在煤基质表面竞争吸附的热力学分析

摘要

利用煤表面自由能变化值和等量吸附热评价了25、30、40℃条件下CO2在煤层中优先吸附性以及CO2与CH4竞争吸附机理。煤吸附CO2后的表面自由能变化值要普遍大于煤吸附CH4后的表面自由能变化值,揭示了单位面积煤基质表面对CO2吸附量要高于对CH4吸附量的热力学本质;通过变换CO2和CH4的等量吸附曲线,得到煤样对CO2和CH4的初始等量吸附热值Qst0分别为48.2 kJ/mol和33.4 kJ/mol,揭示了煤对CO2的吸附作用力要强于CH4,并且煤对CO2的等量吸附热随吸附量的增加呈现增加趋势,与吸附气体分子间的相互作用力相关,表明CO2在煤基质表面存在多分子层吸附。%Based on the calculation of surface free energy change and isosteric heat of adsorption,affinity of coal with CO2 and adsorption capacity differences of coal for CO2 and CH4 were theoretically investigated by using the isothermal adsorption test data at 25,30 and 40 ℃ conditions.Compared to adsorption of CH4 and CO2 on coal matrix generally gave rise to more surface free energy change of coal,implying the thermodynamics of coal matrix have more adsorption capacity of CO2 than that of CH4 per unit surface area.The initial isosteric heat of adsorption（Qst0） that was able to quantify adsorption force of coal and gas was calculated by transforming adsorption isosterics curve of coal for CO2 and CH4.The initial isosteric heat of CO2 and CH4 adsorption on coal matrix was 48.2 and 33.4 kJ/mol respectively,so more adsorption force existing between CO2 and coal was concluded.Due to the inter-gas molecules force,isosteric heat of adsorption of CO2 increases with the increasing of adsorption volume,which indicates that multi-molecule layer adsorption happens during the adsorption of CO2 on coal matrix.