Study on the Mechanism of H2S Adsorption by Different Functional Groups of the Coal Surface Based on Density Functional Theory, Gran Canonical Monte Carlo, and Molecular Dynamics

In order to reveal the relationship between different functional groups and the adsorption performance of H2S molecules at the molecular level and to investigate the influence mechanism of H2S molecule adsorption characteristics, Materials Studio was used to study the adsorption characteristics of different functional groups: hydroxyl, carboxyl, carbonyl, ether bond, pyridine, pyrrole, thiophene, methyl, benzene, mercaptan, thioether, sulfone, and sulfoxide on H2S gas based on the methods of grand canonical Monte Carlo (GCMC), molecular dynamics (MD), and density functional theory (DFT). Research has shown that the absolute values of adsorption energy, from high to low, are Ph–COOH > Ph-pyridine > Ph-pyrrole > Ph–OH > Ph–C–O–C > Ph–C═O > Ph > Ph-methyl > Ph-sulfoxide > Ph-mercaptan > Ph-sulfone > Ph-thioether > Ph-thiophene > H2S–H2S. The adsorption of H2S by functional groups is the result of a combination of physical and microchemical adsorption. In the early stage of adsorption, functional groups attract H2S gas molecules through electrostatic and van der Waals forces, causing H2S molecules to approach the functional group. When approaching the hydrogen bonding range of 0.26–0.31 nm, electron transfer occurs between functional groups and H2S molecules, and hydrogen bonding occurs between carboxyl, carbonyl, hydroxyl, pyridine, sulfone, and sulfoxide functional groups and H2S molecules, resulting in microchemical interactions. The potential energy curves of functional groups and H2S molecules conform to Lennard-Jones theory, and the order of saturated adsorption capacity and adsorption energy is consistent. H2S molecules have obvious layering characteristics in narrow pores.