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 13 C 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.

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Four coals samples at different ranks were analyzed by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and solid-state 13C nuclear magnetic resonance (NMR). The calculated coal molecular model was constructed according to the experimental data. The mode of evolution of four coal molecules with different metamorphic degrees was explored. The results indicate that the nanostructures of these four coal molecules mainly consist of aromatic structures, aliphatic structures and oxygen-containing functional groups. The coal metamorphic degree is the most important factor affecting the evolution of the coal molecular nanostructure. By increasing the coal rank, the aromatic carbon content and aromatic system increase, while the aliphatic carbon content and aliphatic system decrease, and the species and content of oxygen containing functional groups are also reduced. During the evolution of the molecular microcrystalline structure, the degree of vertical order of the aromatic structural unit, the flatness of the aromatic structural unit (La), the average crystallite stacking height (Lc), and the average number of crystallites in a stack (n) increase, while the interlayer distance between aromatic sheets (d002) decreases; the short-range ordering of the coal structure is mainly caused by changes in the orientational arrangement from intramolecular aromatic layers to intermolecular aromatic layers when low-rank coal molecules evolve to high rank coal molecules. The structural evolution mechanism of coal molecules of different ranks has been revealed through the analysis of the mode of evolution of the molecular structure the coal. This study enables us to better understand the nanostructure evolution mechanism of coal molecules at different ranks.