Abstract
In order to clarify the microscopic dynamics mechanism of CH(4), CO(2) and H(2)O adsorption and diffusion in coal, and to reveal the mechanism of the influence of different temperatures and pressures on the adsorption and diffusion characteristics of coal adsorbed CH(4), CO(2) and H(2)O molecules. In this paper, the macromolecular structure model of Jixi gas-fat coal was constructed, based on the Giant Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods. The adsorption-diffusion characteristics of CH(4),CO(2) and H(2)O single-component gases in the gas-fat coal macromolecule model at temperatures ranging from 273.15 K to 313.15 K and pressures ranging from 0.01 MPa to 15 MPa were investigated by using Material Studio software. The research results indicated that: The adsorption of three gases, CH(4), CO(2) and H(2)O, increased with the increase of equilibrium pressure, and the adsorption isotherms conformed to Langmuir type I isotherms. The amount of saturated adsorption of CH(4) ranged from 11.18 to 14.37 ml/g, the saturated adsorption of CO(2) ranged from 20.40 to 24.70 ml/g, and the saturated adsorption of H(2)O ranged from 66.61 to 84.21 ml/g. With the increase of temperature, the saturated adsorption of CH(4) and CO(2) both decreased, and the saturated adsorption of H(2)O firstly increased and then decreased, and the adsorption of H(2)O by low temperature and high temperature had both an inhibitory effect on the adsorption of H(2)O. The potential energy distributions of CH(4), CO(2) and H(2)O molecules are poisson distributed. The absolute values of the most available interaction energies are, from highest to lowest: H(2)O > CO(2) > CH(4); the activation energies for diffusion of CH(4), CO(2) and H(2)O are 12.20 kJ/mol, 3.36 kJ/mol, and 8.47 kJ/mol, respectively, and the diffusion of CO(2) is the more likely to occur. The adsorption of CH(4) and CO(2) in coal is physical adsorption, while the adsorption process of H(2)O molecules is beyond the scope of physical adsorption. The absolute value of the interaction energy is H(2)O > CO(2) > CH(4) in descending order.