Molecular simulations insight into oxygen-containing groups' impact on CO₂, CH₄ and N₂ adsorption in Ordos Basin deep...

CO₂/N₂-enhanced coalbed methane recovery serves as a key approach to boosting coalbed methane production. Gaining insight into the adsorption behavior and microscopic interaction mechanisms of CO₂, CH₄, and N₂ in coal, along with their impact on coal properties, is therefore crucial. In this study, a series of functionalised coal macromolecular models (CMMs) were developed based on a previously validated anthracite prototype from the Daning-Jixian region. By employing a grand canonical Monte Carlo and density functional theory approach, combined with electrostatic potential (ESP) analysis, we systematically explored how a coal macromolecular model (CMM) modified with oxygen-containing functional groups (OFGs; i.e., -C = O, -COC-, -C, -OH, and -COOH) affects the adsorption of CO₂, CH₄, and N₂. Adsorption energy rankings revealed that OFGs promote CO₂ and N₂ adsorption (COOH-functionalized CMM (COOH-CMM) shows high energy for both) but hinder CH₄ adsorption. Moreover, CO₂ exhibits the strongest adsorption affinity among the three gases, with a maximum adsorption energy slightly higher than that of CH₄ and approximately 2.4 times that of N₂. OFGs, particularly COOH, increase the accessible surface area, the number of binding sites, and affinity, thus facilitating CO₂ adsorption in micropores. This study enriches the understanding of the adsorption potential and microscopic interaction mechanisms of CO₂, CH₄, and N₂ in coal and reveals the crucial role of oxygen-containing functional groups, providing new molecular-level insights into selective CO₂ capture and CO₂/N₂-enhanced coalbed methane recovery.