Molecular simulation of gas adsorption characteristics and diffusion in micropores of lignite

Abstract In order to study the adsorption characteristics of single component, binary and ternary mixed gases in lignite, the microscopic processes of CO2 and N2 injection for CH4 desorption was revealed. In this paper, the molecular models of Shendong lignite (C197H146N2O31) at 273.15, 283.15, 293.15 and 313.15 K were established. Based on the theory of molecular mechanics and dynamics, the adsorption characteristics of lignite were simulated by means of grand canonical Monte Carlo and molecular dynamic methods. The adsorption capacities and configurations of CH4, CO2, N2 and H2O in lignite were obtained, and their corresponding adsorption isosteric heats and diffusion coefficients were calculated. The results show that the adsorption isotherm of a single component gas corresponds well to the Langmuir equation. For multi-component gas adsorption, the competitive adsorption advantage of CO2 is obvious, and adsorption capacity of CO2 is minimally affected by other factors. However, the adsorption capacities of CH4 and N2 respectively are seriously affected by their molar ratios in the mixtures and the moisture content of lignite. The adsorption isosteric heats of CH4, CO2, H2O and N2 decrease with increasing temperature, following the order of H2O > CO2 > CH4 > N2.