Reaction mechanisms involving peroxy radical in the low-temperature oxidation of coal

摘要

The mechanisms whereby peroxy radicals (ROO.) participate in the low temperature oxidation of coal have been probed. Through charge distribution analysis, structural parameters, and frontier orbital analysis, the existence of active sites has been proven. Model optimization, transition-state calculations, and IRC verification was carried out on common reaction processes involving ROO. in coal. Quantum chemical calculations were applied to evaluate and analyze thermodynamic parameters. The results of these calculations showed that chemical adsorption of O2 on aliphatic hydrocarbon free radicals produced ROO.. This chemical adsorption process was associated with a zero-level energy barrier at room temperature, and its enthalpy change was -132.64 kJ/mol. The abstraction of H by ROO. was divided into H transfer between adjacent groups and within a group. Our calculations showed that H transfer within a group had to overcome an energy barrier of 162.14 kJ/mol, the heat release was 135.23 kJ/mol, and the reaction rate constant was 2.34 x 10-14 s- 1 M- 1. H transfer between adjacent groups overcame an energy barrier of 116.39 kJ/mol, the heat absorbed was 35.96 kJ/mol, and the reaction rate constant was 2.45 x 10-6 s- 1 M-1. A compound antioxidant enzyme inhibitor containing superoxide dismutase (SOD) was used to eliminate ROO.. SOD could undergo a disproportionation reaction to eliminate ROO. with an energy barrier of 31.3 kJ/mol. This implied that SOD should automatically eliminate ROO. at room temperature. Our research results helped to further understand the mechanism of ROO. participation in the reaction and provide theoretical support for the coal spontaneous combustion prediction.