Molecular simulation study on multicomponent competitive adsorption of CH4, CO2, and H2O in coal

Coal exhibits heterogeneous pore networks and chemically diverse surfaces, resulting in complex competitive adsorption among CH 4 , CO 2 , and H 2 O. The underlying molecular mechanisms remain unclear. In this work, molecular simulation methods were applied to investigate the adsorption behavior and interaction characteristics of CH 4 /CO 2 /H 2 O mixtures on two typical coal components (inertinite and vitrinite) under different CO 2 enrichment levels, corresponding to gas-phase CO 2 mole fractions of 4.8%, 9.1%, and 16.7%. The results demonstrate that CH 4 dominates surface occupation in all cases, maintaining 30–70 adsorbed molecules, whereas CO 2 adsorption is significantly weaker, remaining below 5 at low loading and increasing to only 10–17 at high loading. This indicates a limited competitive capability of CO 2 for adsorption sites. From an interaction perspective, water governs the electrostatic environment, with surface–water Coulombic energies consistently distributed around − 600 to − 750 kJ mol −1 . In contrast, CO 2 –water interactions decrease from − 220 to − 360 kJ mol −1 to − 100 to − 170 kJ mol −1 as CO 2 loading increases, reflecting a pronounced screening effect. Meanwhile, direct CO 2 –surface interactions remain weak (typically − 5 to − 15 kJ mol −1 ). Overall, CH 4 adsorption is primarily controlled by dispersion interactions, while CO 2 is constrained by weak surface affinity and reduced hydration strength, resulting in a secondary role in multicomponent competitive adsorption within coal systems.