Structural Evolution and Thermal Reactivity of Kerke Coal: Molecular Model Construction and Multi-Technique Characterization

To clarify the structural evolution and thermal reactivity of Yili Kerke coal, raw and heat-treated samples were analyzed. Characterization combined proximate and ultimate analyses, TG, FTIR, XPS, ¹³C-NMR, and HRTEM. A molecular model with the formula C₁₇₉H₁₃₂N₂O₁₃ was constructed from multiscale structural parameters to represent the average chemical structure of Kerke raw coal. After classical molecular mechanics (MM) and molecular dynamics (MD) optimization, the lowest-energy configuration sampled had a total energy of 661.38 kcal mol⁻¹. The periodic aggregate model had a density of 1.31 g cm⁻³. The ignition and burnout temperatures of the coal samples generally increased after thermal treatment. The microstructural evolution exhibited distinct stages. At low temperatures, aromatic carbon dominated, with adjustments in functional group and aromatic fringe distributions. At medium temperatures, oxygen-containing components and aromatic carbon types were redistributed, and the proportion of short fringes increased. At high temperatures, aromatic structures became more concentrated, aliphatic carbon decreased, and the proportion of larger aromatic fringes increased overall. Macroscopic thermal analysis and microstructural characterization jointly reveal that molecular structural evolution is consistent with thermal reaction characteristics at different stages. These findings provided a molecular-scale basis for understanding the oxidative thermal behavior of Kerke coal.