Correlation between highly active carbon-containing solid free radicals and spontaneous combustion reactivity of coal

The evolution behavior of free radicals in coal after the low-temperature oxidation process has been widely studied in order to explore the mechanism of coal spontaneous combustion. However, due to the influence of oxidation, the free radicals measured at room temperature are mostly non-reactive free radicals in coal, and their evolution rules cannot directly reflect the oxidation process of coal. How to measure highly active free radicals in coal at room temperature becomes the focus of research. Therefore, three coal samples with different spontaneous combustion tendencies were used, by combining macro and micro means, to analyze the gas products and free radical parameters of coal samples during low temperature oxidation and low temperature pyrolysis, in order to establish the correlation between carbon free radicals in coal and spontaneous combustion reactivity. Firstly, the spontaneous combustion tendency, oxidation and pyrolysis gas products of coal samples were analyzed, and then the free radical parameters of coal samples were tested by electron paramagnetic spectroscopy. The free radical profiles were fitted by peaks to compare the free radical parameters and the changes of various free radical concentrations during the process. It is found that, on a macro level, CO and CO2 are produced in the process of low temperature oxidation and low temperature pyrolysis, but their gas production volume fraction are different. After pyrolysis, a large number of gaseous oxidation products such as CO and CO2 are immediately produced during the normal temperature oxidation of coal samples. Indicating that coal pyrolysis yielded highly active substances, which can quickly oxidize with air at room temperature. Microscopically, The free radicals in the process of low-temperature oxidation of coal samples were affected by the chain reaction, the correlation between free radical parameters and spontaneous combustion characteristics is weak, However, The increase of alkyl free radicals and total free radicals produced by thermal decomposition can accurately reflect the spontaneous combustion characteristics of coal. Finally, alkyl radicals in coal were verified as highly active carbon solid radicals by oxidative free radical test at room temperature after pyrolysis, and its content was positively correlated with the spontaneous combustion characteristics of coal. The detection of highly active and carbon-containing solid free radicals at room-temperature was realized. The analysis method of coal spontaneous combustion characteristics based on the increase of highly active and carbon-containing solid free radicals concentration was proposed. The research provides significant importance for the discussion of the spontaneous combustion mechanism and development of highly efficient materials for coal spontaneous combustion supression.