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By establishing the molecular structure model of Pingdingshan bituminous coal（Ｃ108Ｈ71Ｏ4Ｎ）, using the grand canonical ensemble Monte Carlo method, the isobaric adsorption curves of the adsorption capacity at temperature of 298.15 and 303.15 K and the adsorption pressure at saturation and the isobaric adsorption curves of 1 point every 10 ℃ between 10 ℃and 70 ℃ were studied at molecular scale. The results show that the physical adsorption capacity of oxygen is negatively correlated with the equal adsorption heat, and positively correlated with low pressure. Adsorption saturation can be achieved at a certain pressure. The adsorption capacity changes relatively little at normal temperature and pressure. The three-dimensional distribution and energy distribution of the density of physical adsorption of oxygen in coal, the diffusion coefficient of O2 molecule in coal, and the influence of aromatic functional groups and fatty functional groups on the physical adsorption of oxygen are obtained. It is found that pyrrole functional groups have a great influence on the adsorption capacity, so as to intuitively understand the behavior of physical adsorption of oxygen by coal.

In order to further clarify the adsorption thermodynamic characteristics of CH4 and CO2 in coal, the giant canonical ensemble Monte Carlo method was used to simulate the adsorption behavior of CH4 and CO2 in coal at different temperatures and different moisture content. The results show that the adsorption capacity of CH4 and CO2 in coal molecules decreases with the increasing temperature and moisture content. By comparing the adsorption amounts of the two components, it is found that both high temperature and the presence of water molecules are not conducive to displace CH4 by CO2; the average adsorption heat of CH4 is negatively correlated with temperature and water content, and average adsorption heat of CO2 has a negative correlation with temperature and a positive correlation with water content. Water molecules are more inclined to react with CO2; the overall adsorption potential of CH4 and CO2 is negatively correlated with temperature and moisture content. When the pressure is low, the adsorption potential of CO2 increases slightly with the increasing of temperature; the adsorption entropy of CH4 and CO2 increases with the increasing of temperature and decreases with the increasing of moisture content. The influence of water on CO2 is stronger than CH4. When two components are injected, the existence of water molecules makes the whole system more stable, which is not conducive to CH4 output.