Influence of Organic Sulfur on CO ₂ Adsorption in High-Sulfur Coal: A Combined Experimental and Molecular Simulation Study

To investigate the effect of sulfur content on CO2 adsorption in high-sulfur coal, coal samples were selected from the 7#, 17#, and 21# seams of the Sanhejian Coal Mine, all with similar metamorphic degrees. Analyses including organic elemental analysis, X-ray photoelectron spectroscopy (XPS), and 13C nuclear magnetic resonance spectroscopy (13C NMR) were conducted. Coal molecular models were constructed using ACD, gMNR, and Materials Studio. The Grand Canonical Monte Carlo (GCMC) method was conducted to calculate the adsorption capacity, adsorption heat, adsorption potential energy distribution of CO2 and CH4 under varying pressures. Different functional groups were grafted onto graphite molecules to simulate the CO2 adsorption energy. The results indicated that with increasing pressure, the CO2 adsorption capacity of samples increased, while the adsorption heat initially decreased and then increased. Both parameters of CO2 were higher than CH4. –COOH, benzene, thiophene, pyrrole, and pyridine exhibited stronger CO2 adsorption capacities than neutral oxygen-containing functional groups (–OCH3, –C═O, –OH) and aliphatic groups (–CH3, –CH2CH3). Inorganic sulfur influences the physical CO2 adsorption capacity of high-sulfur coal by affecting the development of pore and fracture structures, but this effect is limited. Organic sulfur interacts with CO2 molecules through Lewis acid–base interactions and dipole–quadrupole interactions, and exerts a synergistic effect with oxygen-containing functional groups on the coal matrix surface, thereby promoting the chemisorption of CO2 in high-sulfur coal. Furthermore, organic sulfur acts as cross-linking points within the coal macromolecular network, facilitating pore formation and development, which in turn enhances the CO2 adsorption capacity of high-sulfur coal. This study elucidates the CO2 adsorption mechanism in high-sulfur coal and identifies four types of mechanisms by which organic sulfur promotes CO2 adsorption, providing an important reference for the identification of new geological bodies for CO2 sequestration.