Molecular Model Construction and Study of Gas Adsorption of Zhaozhuang Coal

Many gas emission accidents have occurred in the Zhaozhuang coal mine in recent years, so an experiment and simulation study on Zhaozhuang coal adsorption of gas were conducted to explore the adsorption mechanism to allow for the prediction and prevention of gas accidents. The Zhaozhuang coal molecular model was constructed based on a proximate analysis, ultimate analysis, X-ray photoelectron spectroscopy (XPS), and solid-state C-13 nuclear magnetic resonance spectroscopy (NMR). Molecular mechanics (MM) and molecular dynamics (MD) were applied to optimize the chemical structure model of the coal molecule, and the periodic boundary condition was added via the relationship between energy and density. The adsorption behavior of methane in a single coal molecule was studied using the Grand Canonical Monte Carlo (GCMC) method. The experimental method was used to study the adsorption of gas from Zhaozhuang coal. The results show that the aromatic compounds mainly exist in the form of a benzene ring; the aliphatic structure mainly exists in the form of aliphatic side chains and cycloalkanes; oxygen atoms exist in the form of carbonyl group, ether group, and carboxyl group; and nitrogen atoms exist in the form of pyridine and pyrrole in the coal molecular structure. The final density of the Zhaozhuang coal molecular model is 1.15 g/cm(3). The relative adsorption error of the Langmuir adsorption constant (a) is 3.303%, indicating that it is feasible to study the adsorption behavior of methane by constructing coal molecules. A saturated state is reached after absorbing eight methane molecules per coal molecule. The adsorption of methane by the oxygen functional group in the coal molecule is caused by both the adsorption position and the adsorption direction, where the carbonyl group has the greatest influence on adsorption of methane. The results of the simulated adsorption have a good predictive effect on the gas pressure, gas content, gas extraction, and gas disasters in the mining area.