Molecular simulations of multivariate competitive adsorption of CH4, CO2 and H2O in gas-fat coal

There is a physical process of CH4, CO2 and H2O multi-gas competitive adsorption in the process of injecting flue gas or CO2 to enhance coalbed methane recovery. In order to clarify the microscopic mechanism of the competitive adsorption of CH4, CO2 and H2O, a macromolecular structure model of Jixi gas-fertilized coal was constructed in this paper, and the competitive adsorption behaviors of binary and ternary mixed-component gases with different molar volume fractions were investigated by using the Giant Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods at the temperature of 293.15 K. To analyze the laws of pressure, volume fraction and competition between different gas components for the effect of adsorption amount, isosteric heat of adsorption, interaction energy, energy distribution, probability density distribution, and adsorption selectivity coefficient. The results showed that under the same conditions, the adsorption amounts from high to low were H2O>CO2 >CH4. The adsorption amounts of each gas component increased with the increase of volume fraction. The adsorption selectivity coefficient decreases with increasing equilibrium pressure and increasing molar volume fraction of strongly adsorbed gas.CO2 and H2O occupy the adsorption sites of CH4, making the CH4 adsorption space smaller and the adsorption sites more concentrated. The interaction energy increases with the increase of the molar fraction of strongly adsorbed gases in the multifunctional system.