Characteristics of antioxidant temperature-sensitive hydrogel inhibiting coal spontaneous combustion

Abstract

Improving the efficiency of inhibition of coal spontaneous combustion (CSC) by inhibitor can efficiently reduce the occurrence of gas explosions, water, soil resources and environmental pollution. In this study, melatonin (MT), a potent scavenger of coal activated free radicals, was integrated into a temperature-sensitive hydrogel (A₅₀) at specific ratios (MT:A₅₀ = a:b), further enabling the preparation of antioxidant temperature-sensitive hydrogel inhibited coal (In-coal (MT:A₅₀ = a:b)). The retardation and scavenging ability of the In-coal (MT:A₅₀ = a:b) on coal oxygen-reactive radicals was analysed by electron spin resonance, and the preventive effect on the overall oxidation process was analysed by thermogravimetric experiments. It was shown that the In-coal (MT:A₅₀ = a:b) was able to maintain the coal in a low-oxygen state at low temperatures, causing a large reduction in the amount and type of stabilising radicals in the inhibited coal within 90–150 °C. When MT dominates in In-coal(MT:A₅₀ = a:b), the free radical scavenging ability of MT in the low temperature oxidation stage allows the In-coal(MT:A₅₀ = a:b) to function mainly in the initial mass loss stage, extending the characteristic temperature and average apparent activation energy ($\overline{E_{\text{a}}}$) of the In-coal(A₅₀), in which In-coal(MT:A₅₀ = 3:1) has the optimal preventing effect in this stage. Compared with the raw coal, it can extend the maximum water loss rate temperature by 10.46 °C and increasing the $\overline{E_{\text{a}}}$ by 114.99 kJ/mol. The slow oxidation stage reduces the contact between the coal and oxygen due to the oxygen-depleted environment created by the gel phase transition, and under the enhancing effect of MT in removing coal reactive free radicals, the dry cracking temperature of the In-coal(MT:A₅₀ = a:b) can be extended by up to 18.55 °C and the $\overline{E_{\text{a}}}$ can be increased by a factor of up to 1.40. In terms of the overall combustibility index of the coal, the addition of MT reduces the A₅₀ as a high molecular material pyrolysis leads to high combustion properties and reduces the overall combustibility of the In-coal(MT:A₅₀ = a:b). The results provide important theoretical and engineering support for the effective prevention and control of CSC.