Abstract: The adsorption and diffusion behaviors of methane, carbon dioxide and hydrogen sulfide in NaX zeolite at different temperatures and pressures were studied by using grand canonical Monte Carlo method and molecular dynamics method. The adsorption isotherms, adsorption energy curves, probability density distributions and radial distribution function data were obtained. The results of single component adsorption simulation showed that the order of saturated adsorption capacity of NaX zeolite to three kinds of molecules was hydrogen sulfide＞carbon dioxide＞methane. The results of the mixed component adsorption simulation showed that the adsorption strength of hydrogen sulfide was the highest, followed by carbon dioxide, both of which were much stronger than that of methane. Hydrogen sulfide and carbon dioxide molecules were mainly distributed in supercages, while methane was mainly distributed in β cages. The order of the diffusion resistance of the three molecules in the channel was carbon dioxide＞hydrogen sulfide＞methane. The results of radial distribution function analysis showed that the O atom in carbon dioxide interacts more strongly with active sites in zeolite than with C atom. The S atom in hydrogen sulfide is more likely to contact and interact with sodium ions in the pore, while methane is less likely to interact with the active sites in the pore due to its tetrahedral structure.

Key words: natural gas, NaX zeolite, adsorption, diffusion, molecular simulation