Competitive Adsorption Mechanism of CH4, CO2, and N2 in Different Coal Slit Pores Based on GCMC and MD

It is essential to elucidate the meaning of the mechanism of gas adsorption, diffusion, and seepage in the coal microscopic pore structure for efficient gas extraction, disaster prevention and control, coalbed methane resource assessment, and CO2 geological storage. This paper aims to examine the competitive adsorption mechanisms of CH4, CO2, and N2 across different slit pore sizes. The study focuses on the competitive adsorption behaviors of these gases within various slit pore sizes, utilizing Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods. The effects of pressure, slit pore size, and molar volume fraction on CH4, CO2, and N2 adsorption, energy distribution, and adsorption volumetric strain were analyzed. The results indicated that as the slit pore size increased from 0.4 to 8.0 nm, the saturated adsorption capacities showed an increase for CH4 from 12.58 to 53.65 mL/g, for CO2 from 16.94 to 144.5 mL/g, and for N2 from 12.25 to 51.93 mL/g. When the pressure was 10 MPa, the volume strains of pure CO2, CH4 and N2 were 4.73, 1.42, and 1.27%, and the adsorption and swelling capacities of CO2 were 3.33 times those of CH4 and 3.72 times those of N2.