Influence of CO₂ Exposure on High-Pressure Methane and CO₂ Adsorption on Various Rank Coals: Implications for CO₂ Sequestration in Coal Seams

Abstract

There exist complex interactions between coal and CO₂ during the process of CO₂ sequestration in coal seams with enhanced coalbed methane recovery (CO₂-ECBM). This work concentrated on the influence of CO₂ exposure on high-pressure methane and CO₂ (up to 10 MPa) adsorption behavior of three types of bituminous coal and one type of anthracite. The possible mechanism of the dependence of CO₂ exposure on adsorption performance of coal was also provided. The results indicate that the maximum methane adsorption capacities of various rank coals after CO₂ exposure increase by 3.45%–10.37%. However, the maximum CO₂ adsorption capacities of various rank coals decrease by 9.99%–23.93%. TG and pore structure analyses do not observe the obvious changes on the inorganic component and pore morphology of the coals after CO₂ exposure. In contrast, CO₂ exposure makes changes in surface chemistry of the coals, according to the results from FTIR analysis, which is the main reason for increases in the maximum adsorption capacity of methane and decreases in the maximum adsorption capacity of CO₂ for the coals after CO₂ exposure. The different role of CO₂ exposure on methane and CO₂ adsorption is detrimental to CO₂-ECBM. Thus, the implementation of CO₂-ECBM must take into account the influence of CO₂ exposure on the adsorption performance of the target coal seams