Investigation of the physicochemical inhibitors on coal spontaneous combustion based experimental and quantum chemical methods

Aimed at the deprived research on physicochemical synergistic inhibition and the micromechanism of inhibition. The inhibitory effect and mechanism of MgCl 2 , TPPI and the combination of them were studied in this research. Low-temperature oxidation gas production experiment and synchronous thermal analyzer were used to analyze the inhibition and thermal behavior effects of different inhibitors, respectively. Fourier transform infrared spectrometer experiment was used to analyze the changes of the surface functional groups on coal samples before and after inhibition. Density functional theory was used to reveal the inhibitory mechanism of TPPI. In the low-temperature oxidation experiment, the CO release of Composite Inhibitor 5 (TPPI:MgCl 2 = 1:1) treatment coal samples was the least. From the characteristic temperature points and heat release, it can be seen that the composite inhibitor reflects the physicochemical synergistic effect. The addition of MgCl 2 will enhance the inhibitory effect at low-temperature stage (< 400°C) and weaken the inhibitory effect at high-temperature stage (> 400°C). Composite Inhibitor 3 (TPPI:MgCl 2 = 3:7) showed strong inhibitory effect in both low and high-temperature phases, the comprehensive comparison showed the best inhibitory effect. The contents of aliphatic functional groups, hydroxyl groups and carboxyl groups decreased in the coal samples treated by TPPI and composite inhibitor, while the relative contents of stable ether bond and aromatic functional groups increased. The inhibitory mechanism of TPPI is to remove the free radical as R–COO·, R–CO· and R–C· by using itself and its hydrolytic products, to interrupt the chain reaction and finally to inhibit coal spontaneous combustion. The conclusions of this article provide theoretical support for the preparation of physicochemical synergistic inhibitors and the revelation of microscopic mechanism of TPPI inhibition on coal spontaneous combustion.