Effects of Coal Rank on the Adsorption Characteristics and Mechanism of Hydrogen Sulfide by Coal Molecules

Abstract This study systematically investigates the molecular structural characteristics of different rank coals (anthracite, bituminous, lignite) and their adsorption properties and mechanisms toward hydrogen sulfide (H2S). By combining X-ray photoelectron spectroscopy (XPS) and solid-state 13C NMR spectroscopy, it was found that aromatic carbon content increases remarkably from 55.91 to 91.75% with coal rank increasing, whereas aliphatic carbon and oxygen-bearing functional groups decrease accordingly. Macromolecular model representatives corresponding to each coal rank were constructed based on experimental data, and molecular simulation and adsorption analysis were performed using Materials Studio software. Pore structures vary markedly with coal rank: lignite shows the greatest total pore volume but limited connectivity, whereas anthracite develops a well-connected micropore network. H2S adsorption follows the Langmuir–Freundlich model, with capacities decreasing in the order: anthracite > bituminous > lignite. Although the adsorption capacity decreases with increasing temperature, the effect of temperature on the adsorption capacity of different coal grades shows a non monotonic variation. Oxygen-bearing functional groups─particularly carboxyl, hydroxyl, and carbonyl─dominate H2S adsorption via hydrogen bonding, whereas π-electrons of aromatic rings contribute weakly. Molecular dynamics simulations show that the diffusion coefficient of H2S increases with temperature and is highest in anthracite. This study elucidates the influence mechanism of coal rank structure on H2S adsorption behavior at the molecular level, providing a theoretical basis for the treatment of H2S in coal seams.