Adsorption Behavior and Mechanism of CH4 in Micropores in Coal under Different Pressures and Temperatures: A Pore Size Perspective

In order to reveal the pattern of methane adsorption varying with pore size in coal, the grand canonical Monte Carlo method was used to systematically study methane adsorption in pores ranging from 0.7 to 2.0 nm, with intervals of 0.1 nm, considering the effects of temperature and pressure. We find that the pore size is a decisive factor affecting the structure of the adsorbed CH4 in the confined space. Pressure and temperature can significantly affect the structure of the adsorbate only if the pore size is large enough. Pressure has a greater effect on the overall change in the adsorption curve of CH4, which is defined as absolute adsorbed molecular number with pore size compared to temperature, which only has an effect in a specific pore size range. The adsorption mechanism was dominated by solid–liquid interactions when pore sizes ranged from 0.7 to 1.2 nm and was influenced by a combination of pressure and pore volume when pore sizes ranged from 1.2 to 2.0 nm.