Laboratory study on the inhibitory effect of free radical scavenger on coal spontaneous combustion

In this paper, the inhibition of free radical reaction in the coal oxidation process was taken as the starting point, and free radical scavenger 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO) which combines with free radicals very easily to generate inactive substances was regarded as the inhibitor. The occurrence of coal spontaneous combustion was suppressed by inhibiting the chain reaction of free radicals. TEMPO was compared with common halide salt inhibitors through thermogravimetry and differential scanning calorimeter (TG-DSC) thermal analysis, crossing point temperature (CPT), CO production and other data obtained from experiments. The results show that the inhibitory effect of TEMPO is stronger than that of common halide salt inhibitors and the inhibitory effect increases with the rise of TEMPO concentration. The influence of TEMPO on active functional groups in coal at different temperatures was obtained through Fourier transform infrared spectroscopy (FTIR) analysis, suggesting that the inhibitory effect of TEMPO on active functional groups (C-O, C-H, C=O and O-H) in coal gets more significant with the rise of temperature and the increase of active free radicals in coal. On this basis, five common active free radical models were constructed, and their active sites and thermodynamic parameters were calculated according to density functional theory (DFT). The calculation reveals that compared with oxygen-containing free radicals, alkyl free radicals are more active in the thermodynamic reactivity with TEMPO. The experiments prove that TEMPO has a very strong inhibitory effect on coal spontaneous combustion, because the combination between TEMPO and alkyl free radicals during coal spontaneous combustion decreases the activity of free radicals and reduces the concentration of active free radicals, thus inhibiting the chain reaction of free radicals.