Inhibitory effect and mechanism of l-ascorbic acid combined with tea polyphenols on coal spontaneous combustion

The inhibitory effects of compound antioxidants (l-ascorbic acid (VC) and tea polyphenols (TP)) on coal oxidation were studied. The characteristics of coal oxidation was investigated by temperature-programmed experiments. The changes of active groups in coal were confirmed by Fourier-transform infrared spectroscopy. Quantum chemical theory was used to explore the reaction mechanism. Experimental results showed that compound antioxidants exhibit significant synergistic inhibition effect on coal oxidation. The apparent activation energy of coal oxidation increases by 16.23 kJ/mol for the addition of 6 wt% compound antioxidants (TP:VC = 2:1). The content of aliphatic hydrocarbons, –OH, CO and COOH in the antioxidant-treated coal decreases, while that of ether bond and aromatic bond increases. H15 of VC or H48 of epigallocatechin gallate (the main component of TP) can readily scavenge oxygen-containing radicals and inhibit the production of active groups in coal. Water-soluble antioxidants can be evenly dispersed on the coal surface, which provides an environment-friendly and efficient approach to preventing coal spontaneous combustion.