Study on the Influence of Hydrogen Sulfide Occurrence on Methane Adsorption Characteristics in High-Sulfur Coal Seams

To elucidate the effect of hydrogen sulfide (H2S) occurrence on methane (CH4) adsorption and diffusion in high-sulfur coal seams, a macromolecular model of high-sulfur coal was constructed based on Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and 13C nuclear magnetic resonance (13C NMR) analyses. Molecular simulations were then performed to investigate the competitive adsorption of H2S and CH4 and the effect of H2S on CH4 adsorption–diffusion behavior. The results show that H2S exhibits a substantially stronger adsorption affinity for the coal matrix than CH4 under single-component adsorption conditions, with adsorption heats of 22.03 and 10.81 kJ/mol, respectively. As the H2S content increases from 0 to 1.5%, the saturated adsorption capacity of CH4 decreases from 7.93 to 7.13 mmol/g, corresponding to a reduction of 10.09%. As the hydrogen sulfide content increases, the adsorption sites for methane molecules in coal decrease, the interaction energy during methane adsorption increases, and the diffusion coefficient of methane molecules decreases. These findings demonstrate that H2S can significantly inhibit CH4 adsorption and diffusion in high-sulfur coal, providing molecular-scale insights into the competitive adsorption and transport mechanisms of mixed gases in sulfur-rich coal seams.