The influence of methane on the development of free radical during low-temperature oxidation of coal in gob

• Free radicals relate to both oxygen and methane in the oxidation environment. • The g-factor grows with the rising methane and the oxidation temperature. • The rising methane changed the free racial type during coal oxidation in gob. • Free radical concentration decreases with methane and increases with temperature. Methane dilutes the oxidation environment of coal in the gob, thus affecting the free radical reaction in low-temperature oxidation of coal. To investigate methane’s effects in this process, three coal samples (i.e., anthracite, coking coal, gas-fat coal) were non-isothermally oxidized to different temperatures in methane-containing environments and then analyzed in an electron paramagnetic resonance (EPR) spectrometer. The experimental results demonstrate that the g-factor and free radical concentration were not only related to oxygen but also associated with methane in the oxidation environment. The g-factor grew with the rising methane and the oxidation temperature. With the rising methane, the free radicals of the anthracite changed from carbon-centred radicals to carbon-centred radicals with an adjacent oxygen atom. Besides, the free radical concentration was found to decrease with methane and increase with oxidation temperature. The rising methane restrains the increase of free racial concentration during coal spontaneous combustion. It is inferred that the influence of methane is related to the competitive adsorption of coal on different gases. The results of this study added to our understanding of the role that methane plays in the low-temperature oxidation of coal and can serve as a reference in coal spontaneous combustion prevention in working face gobs with methane emissions.