Low-Temperature Oxidation Mechanism of Coal under Hydrothermal Conditions Based on a PLSR Model

The low-temperature oxidation environment of water-immersed residual coal in high-temperature goafs is complex, yet the low-temperature oxidation mechanism of high-temperature water-immersed coal remains unclear. Therefore, this study employs temperature-programmed experiments combined with in situ infrared spectroscopy to investigate the microscopic mechanism and regulatory factors of low-temperature coal oxidation. Additionally, a partial least-squares regression model was used to establish a quantitative relationship between the microscopic structure and macroscopic oxidation products. The results show that hydrothermal pretreatment induces a synergistic effect of physical structure relaxation and chemical component activation, which reduces the oxidation reaction barrier. Compared with raw coal, the CO₂ yield of W-65 coal at 200 °C increased by 50%, and the apparent activation energy decreased by 18.81%. Hydrothermal action promotes the breaking of aliphatic chains and their conversion into oxygen-containing functional groups. The carbonyl absorption peak intensity in W-65 coal increased by 75.2% compared to that in raw coal. PLSR analysis indicates that carbonyl groups explain 93.7% of the cumulative variance in gas products, showing a positive contribution, and are the key active functional groups dominating the oxidation reaction. Physical swelling improves oxygen transport conditions, and the coupling of these factors leads to an increased risk of spontaneous combustion. This study clarifies the physical-chemical synergistic disaster mechanism of water-immersed coal and provides a theoretical basis for preventing and controlling heat-driven disasters associated with water hazards in deep mines.