Study on the effect of organic small molecules on methane adsorption-diffusion characteristics based on GCMC、MD and DFT

In order to investigate the influence of organic small molecules on the adsorption-diffusion characteristics of methane in coal, the relative content of organic small molecules in Jixi gas-fat-coal was obtained based on extraction experiments, and organic small molecules solutions and gas-fat-coal macromolecule models containing different concentrations of organic small molecules were constructed, and by means of the Grand Canonical Monte Carlo (GCMC), Molecule Dynamics (MD), and Density Functional Theory (DFT) approaches. Material Studio was used to study the adsorption and diffusion behavior of CH4 at a temperature of 298.15 K and a pressure of 1–15 MPa in a gas-fat coal macromolecule model containing different concentrations of Diphenylmethane, Dihydrofuran-2(3H)-one, 2,6-Di-tert-butyl -4-(hydroxymet-hyl) phenol, Dodecane, Ethylcyclohexane, and Vinylbenzene, and to analyze the adsorption diffusion behavior of organic small molecule species and concentration on CH4 adsorption capacity, interaction energy, Isosteric heat of adsorption, energy of adsorption, solubility, pore characteristic distribution, radial distribution function, relative concentration distribution and the diffusion coefficient, and also explored the electrostatic potential distribution of different organic small molecules. It was shown that after the addition of organic small molecules to the macromolecule structure of gas-fat-coal, the free state of organic small molecules occupied the adsorption sites of CH4, and the effective space used for CH4 adsorption was reduced, resulting in the reduction of CH4 adsorption capacity after the addition of organic small molecules. The change in the pore structure of coal caused by small organic molecules is the main factor leading to a decrease in the adsorption capacity of CH4.