Competitive Adsorption and Diffusion Behavior of H2 and CH4 in Anthracite: Insights from Experiment and Molecular Simulation

The competitive adsorption behavior of CH4 and H2 in abandoned coal mines is the core for evaluating the hydrogen storage potential of coal seams. This study first conducted coal petrology, elemental, and industrial analyses on coal samples, characterizing their pores, morphology, minerals, and functional groups to clarify the basic properties of the anthracite. Subsequently, high-pressure adsorption experiments were performed to obtain adsorption isotherms for pure H2 and pure CH4, finding that both exhibit Type I adsorption characteristics, with CH4 showing significantly higher adsorption capacity than H2. Further, based on the macromolecular model of anthracite, grand canonical Monte Carlo simulations and molecular dynamics were employed to systematically analyze the adsorption properties of single-component gases and H2/CH4 binary mixtures in the anthracite matrix under conditions of 293.15–333.15 K and 0–10 MPa. Simulation results indicate that the absolute adsorption amount of CH4 in single-component systems was approximately 3 times that of H2. In binary competitive systems, CH4 preferentially adsorbs onto the coal matrix; the total adsorption amount of the mixed gas correlates positively with the CH4 molar fraction, while CH4 adsorption decreases and H2 adsorption increases with rising temperature. The adsorption selectivity coefficient SCH4/H2 remained greater than 1 and decreased with increasing pressure and temperature. The presence of CH4 molecules in coal seams increases the diffusion resistance of H2. This study reveals the influence of CH4 on hydrogen storage behavior in coal from both experimental and molecular simulation perspectives, providing a theoretical basis for optimizing hydrogen storage in deep abandoned coal mines.