Study on the synergistic inhibitory mechanism of inhibitor ions and their hydration layers on oxygen-containing functional groups in coal

In order to explore the synergistic inhibitory mechanism of oxygen-containing functional groups in coal by anions, cations and water molecules in the inhibitors, the action mechanism of 20 % CaCl2 and Na2SO4 solutions on coal is studied from macroscopic and microscopic levels by using methods such as temperature-programmed oxidation experiments, TG-DSC, FTIR, and molecular simulation. The results show that the inhibitory effect of a 20 % CaCl2 solution is better. Its average inhibition rate within the range of 40 °C–180 °C reaches 78.94 %. Compared with raw coal, the ignition temperature is delayed by 31.31 °C, and the proportion of oxygen-containing functional groups decreases by 38.14 %. To further reveal its microscopic inhibition mechanism, theoretical analyses are conducted on the coal models and the equilibrium configurations of their interaction with anions, cations in the inhibitors and their hydration layers using molecular dynamics and quantum chemistry methods. It is found that when the anion and cation act on the active group, they and their hydration layers act synergistically. On the one hand, they isolate the contact between coal and oxygen through physical hygroscopicity. On the other hand, they stabilize the active groups through intermolecular interactions. Thus, the inhibitory effect is effectively improved and the process of oxidation and spontaneous combustion of coal is delayed.