Chemical structure characterization and molecular model construction of lean coal

In order to utilize high-rank coal efficiently and cleanly, based on Shanxi lean coal, this paper explores the molecular structure characteristics of lean coal and constructs a molecular model of lean coal. In this paper, X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance carbon spectroscopy （¹³C NMR） were used to characterize and analyze the element occurrence and carbon atom structure of lean coal, and a macromolecular model of lean coal was constructed and optimized. The results showed that the molecular aromatic structure of lean coal was composed of 1 naphthalene, 8 anthracene, 1 tetraphenylene, 1 pyrene, 2 pyridine, 2 pyrrole and 1 thiophene. The oxygen-containing structure includes two intramolecular oxygen-bonded aliphatic carbons, two oxygen-substituted aromatic carbons and one carbonyl carbon. Aliphatic hydrocarbons are composed of 2 fatty methyl groups, 3 aromatic methyl groups, 2 methylene groups and 4 methylene groups. The final macromolecular model of lean coal is C₂₀₀H₁₄₀O₅N₄S. After the initial model was optimized, the valence energy and non-bond energy of coal molecules decreased, but the valence electron energy of coal molecules in the final model was higher than that of non-bond energy, which was the main part of the total energy. Therefore, from the point of view of the adsorption space that the surface of lean coal can provide for gas, the adsorption advantage of CO₂ gas in lean coal is stronger than CH₄ gas.