Molecular simulation study on competitive adsorption characteristics of CO2 and CH4 for 8# coal in Dongqu Mine

A deep understanding of the micro mechanism of competitive adsorption of CO2 and CH4 in coal seams is crucial for achieving CO2 displacing methane extraction （CO2-ECBM）. Based on the macromolecular structure model of Dongqu Mine No. 8 coal, a study was conducted on the competitive adsorption of single and dual components of CO2 and CH4. The results indicate that the adsorption capacity of CO2 in single component adsorption is significantly greater than that of CH4, and the total adsorption capacity in dual component competitive adsorption increases with the increase of CO2 mole fraction; the selective adsorption coefficient of CO2 for CH4 in dual component adsorption under different molar ratios is always greater than 1, and the larger the molar fraction of CO2, the smaller the selective adsorption coefficient; the interaction energy significantly increases with the increase of adsorption capacity. The larger electrostatic energy in the CO2 adsorption system promotes the adsorption of CO2 by coal macromolecules. Therefore, the interaction energy of different molar ratio systems increases significantly with the increase of CO2 mole fraction; the adsorption potential of CO2 in single component adsorption is greater than that of CH4, while the adsorption potential of CO2 in dual component competitive adsorption increases with the increase of CO2 molar ratio, while the adsorption potential of CH4 decreases with the increase of CO2 molar ratio. This result is consistent with the results of adsorption selectivity analysis.