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Mechanistic Study of the Inhibition of Active Radicals in Coal by Catechin

ABSTRACT In order to inhibit the active free radicals in the oxidation process of coal at low temperatures, the use of catechin as inhibitors is proposed. A set-up of thermogravimetric analyzer-Fourier-transform infrared spectrometer-gas chromatograph/mass spectrometer (TG-FTIR-GCMS) has been used to measure mass loss and the gaseous products evolved during the heating of raw coal and coal-catechin samples. The experimental results show that epicatechin (EC) can provide H· combined with active free radicals in coal, thereby inhibiting the reaction of free radicals with oxygen, leading to the disappearance of the mass gain stage of coal samples. Compared with raw coal, the content of carbon oxides gaseous products released from coal-catechin sample was significantly reduced at the same temperature. Molecular structure models of EC and active free radicals (including C7H7·, C7H5O·, and C7H7O·) in coal have been constructed by GaussView software. Using the quantum chemical method for analysis, the charge distribution of EC is obtained, and it is concluded that the hydroxyl group of epicatechin (EC) is the active site and can provide H· and EC·for scavenging free radicals. To simplify the analysis, the most active meta-hydroxyl group on the B-ring is chosen to reveal the activity of EC. The reaction processes of H·/EC· combining with C7H7·/C7H5O·/C7H7O· active radicals respectively have been analyzed. It is concluded that catechin could convert active radicals into inert compounds or stable radicals to interrupt free radical chain reaction. Through the calculation of the enthalpy changes and Gibbs free energy changes in the reaction processes, the results showed that H· having higher reactivity is the main factor for inhibiting the spontaneous combustion of coal.