The adsorption and diffusion mechanisms of CH4 and CO2 in heat-treated coal to increase CO2 sequestration potential

CO₂ sequestration in coal seams is a promising strategy for reducing atmospheric CO₂ emissions. However, coal spontaneous combustion(CSC) alters the coal structure, influencing CH₄ and CO₂ adsorption behavior and affecting sequestration efficiency. This study investigated the adsorption and diffusion characteristics of CH₄ and CO₂ in coal subjected to heat treatment(0-500 ℃), simulating CSC effects. Isothermal adsorption experiments(1–8.5 MPa, 30 ℃), proximate analysis, and scanning electron microscopy(SEM) were employed to analyze structural modifications and gas interaction mechanisms. Results revealed that heat treatment significantly enhanced CO₂ adsorption capacity, reaching up to 30 times that of CH₄ at elevated pressures(8.5 MPa). The diffusion coefficients for both gases initially declined with heat exposure but increased at higher temperatures, with CO₂ diffusion being up to 7.2 times greater than CH₄. Structural analysis indicated the development of micropores and the removal of surface debris, contributing to the increased adsorption and diffusion capacity. These findings offer valuable insights into optimizing CO₂ sequestration strategies in post-combustion coal seams, supporting sustainable carbon capture technologies.