Adsorption and diffusion characteristics of CH4, CO2, and N2 in micropores and mesopores of bituminous coal: Molecular dynamics

The characteristics of gas loading, diffusion and adsorption in pore models of coal molecules within variety pore sizes were different. The Grand canonical Monte Carlo and Molecular Dynamic were conducted in this paper to investigate the loading, adsorption and diffusion characteristics of CH4, CO2, and N2 in micropores and mesopores. Three micropore models (0.5, 1 and 2 nm) and two mesopore models (5 and 8 nm) were established to study the microscopic mechanism of three gases loading, adsorption and diffusion. The results shown that the loading amounts in pore models increased with increasing pore size. However, the tight adsorption amounts and adsorption heats decreased with increasing pore size. The tight adsorption amounts, loading amounts and adsorption heats all followed CO2 > CH4 > N2. There were exponential changes between isometric heats and loading amounts. The diffusion characteristic of three gases in the pores was CH4 > N2 > CO2, and the larger pores were more conducive to gas diffusion. Radial Distribution Function was implemented to study the action radius between gases and C atoms of coal molecules. There was the smallest effective distance and the largest effective radius between CO2 and C atoms. The action distance between N2 and C atoms was the largest, and the action scope between them was the smallest.