Mechanistic influence of organic sulfur on coal spontaneous combustion

Organic sulfur in coal significantly influences its oxidation behavior and spontaneous combustion tendency, yet the underlying mechanism remains unclear. This study compares high-sulfur (WJZ) and low-sulfur (YD) coals of similar metamorphic degree using temperature-programmed gas chromatography, thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) to analyze gas release and functional group evolution during spontaneous combustion. Density functional theory calculations further explore molecular mechanisms. Results show WJZ coal produces higher CO/CO2 concentrations and lower CH4/C2H6 generation temperatures than YD coal, with a lower critical temperature and maximum mass loss rate, confirming its greater spontaneous combustion propensity. Organic sulfur may enhance oxygen adsorption and oxidation activity, accelerating low-temperature CO/CO2 production. Quantum simulations reveal thiophene, sulfone, and thiol groups increase oxygen adsorption energy (by 1.44–4.81 kJ·mol−1) and reduce reaction energy barriers (1%–1.7%), promoting oxidation. These findings offer theoretical insights for preventing coal spontaneous combustion.