CH_4,CO_2和N_2多组分气体在煤分子中吸附热力学特性的分子模拟

Molecular simulation of adsorption thermodynamics of multicomponent gas in coal

为进一步明确煤分子吸附多组分气体的热力学机制,应用巨正则系综蒙特卡洛(GCMC)模拟方法,从热力学角度研究了不同温度下等比例CH_4,CO_2,N_2多组分气体在煤分子模型中的吸附行为。研究表明:在晶胞内CH_4呈点状分布,CO_2呈簇状分布,N_2呈带状分布; 3种气体的吸附量、吸附热、吸附熵关系均为CO_2>CH_4>N_2,吸附势能CO_2<CH_4<N_2;吸附量与吸附热呈线性正相关关系,吸附热与温度无明显关系;煤分子吸附CH_4,N_2,CO_2的吸附势能与其吸附量成反比,吸附势能不仅受煤分子表面自由粒子色散力影响,也受吸附焓和吸附熵的影响;相同条件下,3种气体的吸附熵与吸附量和温度均呈负相关关系;吸附热力学参数能用来表征煤分子的吸附特性,从热力学角度证实煤分子吸附CO_2优于CH_4和N_2。

In order to explore the thermodynamic mechanism of multicomponent gas adsorption on coal,the Grand Canonical Monte Carlo simulation method was used to study the adsorption behavior of CH4,CO2 and N2 in the coal molecular model at different temperatures from the perspective of thermodynamics.The simu-lation results show that CH 4 shows a dotted distribution,CO2 shows a cluster distribution,and N2 shows a strip distribution in the unit cell.The relationship between the adsorption capacity,adsorption heat and adsorption entropy of the three gases is CO2>;CH4>;N2.And the relationship between the adsorption potential of the three gases is CO2<;CH4<;N2.There is a linear positive correlation between adsorption and adsorption heat.But there is no obvious relationship between the heat of adsorption and the temperature.The adsorption potential of CH4,N2,and CO2 is inversely proportional to the adsorption capacity.The adsorption potential energy is not only affected by the dispersive force of free particles on the surface of coal,but also affected by the enthalpy of adsorption and entropy of adsorption.Under the same conditions,the adsorption entropy of the three gases has a negative correlation with the adsorption quantity and temperature.Adsorption thermodynamic parameters can be used to characterize the adsorption characteristics of coal molecules,also can confirm that the coal adsorption of CO2 is superior to CH4 and N2 from the thermodynamic point of view.