Molecular simulation of adsorption of gas in coal slit model under the action of liquid nitrogen

The adsorption characteristics of coalbed methane have a significant influence on the adsorption properties of porous media, such as coal and shale. In this study, the adsorption capacities of methane (CH4), water (H2O), and nitrogen (N-2) isotherms in the coal slit model were calculated and discussed in detail. A series of grand canonical Monte Carlo simulations were conducted at 77.15 K and pressures of up to 100 kPa to test the effect of various pore sizes (1, 2, and 4 nm). As the breadth of the slit increased, the amount of adsorption decreased. The amount of adsorption was found to be positively related to pressure. The relationship between the adsorption amounts of the three gases was as follows: H2O > CH4 > N-2, an order consistent with the law of isosteric adsorption heat. Gas was more readily adsorbed in the micropores under low-temperature conditions. The slit width had no effect on the adsorption entropy. Moreover, the relationship between the adsorption entropies of the three gases was as follows: H2O < CH4 < N-2. This research provides a foundation for further exploration of shale and coalbed gases.