Characterization of Competitive Adsorption of Multicomponent Gases Injected with CO₂ in a Coal Mine Goaf

Injection of CO₂ into a coal mine goaf is the primary method for inhibiting coal spontaneous combustion and for driving outgas, and gases such as N₂, O₂, and CH₄ in coal are in competition with it, which in turn affects its adsorption effect in coal. In order to enhance the CO₂ suppression and expulsion effect, the competitive adsorption characteristics of multicomponent gases in the coal mine goaf were investigated. We carried out adsorption experiments with a specific surface area analyzer to clarify the adsorption law of coal on different gases, conducted CO₂ adsorption experiments with an in situ infrared device to reveal the role of functional groups, verified the single-component adsorption law with molecular dynamics simulation, elucidated the effect of temperature on the adsorption of multicomponent gases, and summarized the law of CO₂ competition under different pressures. The results showed that the degree of deterioration was negatively correlated with the adsorption capacity, which was N₂ < O₂ < CH₄ ≪ CO₂, and the functional group C=O promoted the adsorption of CO₂. N₂ and O₂ adsorption produced only van der Waals force, and CH₄ and CO₂ promoted electrostatic force, to which CO₂ had an obvious advantage of electrostatic potential. In the competition adsorption process, CO₂ produces the highest heat of adsorption, and the temperature increase affects the ability to positively correlate with the adsorption capacity of the adsorbate. The adsorption point of carbon dioxide is concentrated near the side branched chain, with better substitution of O₂ at P = 1 MPa, while CH₄ is mainly rejected at P = 2 MPa. The advantages of injecting CO₂ as an inert gas into the air-mining zone were elucidated in terms of functional groups, intermolecular forces, heat of adsorption, and adsorption sites, which provide theoretical support for the suppression of coal spontaneous combustion by replacing O₂ and the enhancement of extraction by replacing CH₄.