Characterisation of competitive adsorption of CH4 and CO2 mixed components in a coal body based on molecular simulation

The competitive adsorption behaviour of CH₄ and CO₂ in coalbed methane mining is crucial for the optimisation of CO₂ enhanced coalbed methane recovery (CO₂-ECBM) technology. In this paper, the giant canonical monte carlo (GCMC) method is used to simulate and study the competitive adsorption behaviour of CH₄ and CO₂ mixed component gases at different temperatures, pressures, water contents and molar ratios. The results showed that: the competitive adsorption capacity of CO₂ was significantly stronger than that of CH₄, and the increase of its molar ratios could effectively replace CH₄; The increase of temperature or water contents decreased the heat of adsorption of equivalence of CH₄ and CO₂ as well as the Langmuir parameters a and b, which weakened the adsorption selectivity of CO₂, but the competitive ad-sorption advantage was still maintained; the competitive adsorption ad-vantages of CH₄ were also maintained. However, its competitive adsorption advantage was still maintained; under the conditions of low pressure and high CO₂ molar ratios, CO₂ had the strongest ability to drive CH₄; under the conditions of high pressure and low CO₂ molar ratios, the adsorption selec-tivity coefficient of CO₂ to CH₄ decreased the most; there was an upper limit of saturation in the driving of CH₂ by CO₂, and even if the molar ratios con-tinued to increase, the driving efficiency was still low. There is a sat-uration limit for the substitution of CH₄ by CO₂, and even if the molar ratios of CO₂ continues to increase, the substitution efficiency is not significantly improved. This study reveals the competitive adsorption mechanism between CH₄ and CO₂ at the mo-lecular level, and provides a theoretical basis for optimising CO₂-ECBM technology and improving CBM recovery.