Study on the Influence of Mineral Proportion in Bituminous Coal on the Evolution of Thermodynamic Parameters of CO2 Adsorption

Coal is a complex mixture consisting of organic macerals and minerals. The presence of minerals can give rise to variations in the macromolecular structure of coal, modify its pore structure, and subsequently influence the coal’s adsorption capacity. Taking bituminous coal and kaolinite minerals as the research subjects, this study quantitatively investigated the impact of kaolinite and its content on the adsorption properties of bituminous coal using the molecular dynamics method. Moreover, the pore characteristics and adsorption energy of bituminous coal under different mineral contents were analyzed to uncover the underlying microscopic mechanism.The results demonstrate that as the mass fraction of kaolinite increases, the total volume, free volume, and porosity of the coal macromolecules composed of bituminous coal and kaolinite all increase. Additionally, with an increase in the kaolinite mass fraction, the adsorption capacity of CO2 also rises. The adsorption heat ranges from 24.57 to 32.97 kJ/mol under different mass ratios, and it increases in tandem with the growth of the adsorption capacity. As the mass fraction of the minerals increases, the peak value of the radial distribution function between bituminous coal and kaolinite goes up, indicating that the probability and interaction intensity of CO2 molecules surrounding bituminous coal molecules increase with the rise in mineral content. Kaolinite molecules exhibit a strong interaction with CO2, and CO2 molecules are more densely packed within the kaolinite-containing structures compared to those in bituminous coal. Under the same time conditions, the self-diffusion coefficient of CO2 molecules in the kaolinite-containing structure is higher than that in the bituminous coal structure, suggesting that the adsorbed gas in the kaolinite-containing structure is more stable. Furthermore, as the quantity of kaolinite increases, the porosity grows, and the self-diffusion coefficient of CO2 molecules also increases.This research offers a theoretical reference for coalbed methane (CBM) exploitation and carbon sequestration.