Inhibition Effect and Mechanism of Phenolic Antioxidants on Coal Spontaneous Combustion

Coal spontaneous combustion is a major safety and environmental concern in mining operations. This study systematically evaluated three phenolic antioxidants (BHA, BHT, and PG) as promising inhibitors through multiscale experiments and quantum chemical calculations. Results showed that all antioxidants delayed the coal-oxygen reaction by increasing characteristic temperatures and reducing heat release. For instance, the initial exothermic temperature T₂ was increased by 21.7 °C, 13.71 °C, and 5.02 °C for PG, BHT, and BHA, respectively. A novel comprehensive evaluation system, based on the coal spontaneous combustion risk coefficient (C_r) and destructive coefficient (C_d), identified PG as the most effective inhibitor overall. Analyses via SEM and LTNA showed that PG treatment reduced the coal's specific surface area and pore volume, leading to a densification of its microstructure. This physical alteration contributes an additional oxygen-blocking effect. EPR and in situ FTIR confirmed that these antioxidants act as hydrogen donors, effectively quenching active free radicals (e.g., ·OH, CH₃·) and suppressing the conversion of carbon-centered to oxygen-centered radicals, thereby terminating chain reactions. Quantum chemical calculations corroborated that the reactions between the antioxidants and key radicals are spontaneous and exothermic. The reactivity order was determined as ·OH > CH₃· > Ar-CH₂· > Ar-CH₂-O· > Ar-CH₂-OO. These results elucidated the underlying structure-activity relationship: PG's superior performance is directly attributable to its three phenolic hydroxyl groups, which provide a greater total radical scavenging capacity compared to the single group in BHA or BHT. This study confirms that PG is an efficient, low-cost, and environmentally friendly inhibitor with strong potential to prevent coal spontaneous combustion, providing a theoretical basis for its industrial application.