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.