Adsorption and Diffusion Behavior of CH4 and CO2 in Closed and Open Pores from Zhaozhuang Coal

The adsorption and diffusion properties of CH4, CO2, and H2O in a realistic coal molecule are essential to the study of carbon capture, utilization, and storage (CCUS). The molecular dynamics (MD) simulations and grand canonical Monte Carlo (GCMC) methods were used to investigate the adsorption, diffusion, and relative concentration of gases on the different styles of geometrical pores in closed and open pores under different moisture contents. The results showed that the amount of adsorption in the cylindrical pore was higher than that in the spherical pore. The closed-cylindrical pore had a stronger gas adsorption capacity. Under the same conditions, the diffusion coefficients of gases in the open pores were larger than in closed pores. Methane has a higher diffusion coefficient than CO2. The presence of water reduced the diffusion coefficients of the gases. In the meantime, the gap between the CH4 and CO2 diffusion coefficients gradually decreased as the water content increased. The water molecules occupied the surface and space of pores, leading to reduction in the adsorption capacity. Due to the increasing amount of water, the diffusion coefficient of CH4 and CO2 decreases due to enhanced interactions between C and the gases according to the radial distribution function (RDF).