Study on the kinetics of chemical structure reaction in coal catalyzed by OH free radicals

This study investigated the influence of OH free radicals on the reactivity of aromatic rings and their side chain active groups. Quantum chemistry theory and in situ diffuse reflectance infrared Fourier transform spectroscopy were applied to perform simulations and experiments. Density functional theory was used to calculate the electrophilic substitution of aromatic hydrocarbons of six model structures by OH free radicals. The reactivities of the key elementary reaction of the side chain active group before and after the reaction were compared. The results showed that the reaction energy barriers of the addition and elimination of OH radicals of aromatic hydrocarbons were lower than 40 kJ/mol, indicating that the reactions can occur at room temperature and emit large amounts of heat. The electronic effect of phenolic hydroxyl and benzene rings further improved the reactivity of the aromatic ring C–H. Combining these results with the change rule of the phenolic hydroxyl structure in coal under isothermal oxidation conditions, we conclude that OH radicals participate in the formation of the phenolic hydroxyl structure and further catalyze the oxidation reaction of coal at low temperatures. This finding is significant for the heat storage stage of low-temperature oxidation in coal.