Study on the inhibitory effect of inhibitor based on the coal molecular structure analysis: A case study of Zhundong coal, Xinjiang, China

The aim of this work is to use the changes in coal molecular structure to study the effect and mechanism of inhibitors, and to provide a reference for better preventing and controlling coal spontaneous combustion. In this study, Xinjiang Zhundong coal was used to construct the macromolecular structure. Three inhibitors, CaCl2, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), and 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][OTF]), were selected to be mixed with raw coal, and three different inhibitor concentrations were set for each inhibitor. The changes in the molecular structure of the coal under different inhibitor concentrations and temperature conditions were analyzed by Fourier infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis. ChemDraw and Materials Studio were used to construct a coal molecular structure model with an inhibitor concentration of 20% at 50 ℃. Results showed that the molecular formula of the ZD2-1 is C222H123O39N. The coal molecule contained a higher number of aliphatic hydrocarbon branches and a lower degree of aromatic ring condensation. When heated to 300 ℃, the proportion of adsorbed oxygen in raw coal decreased obviously, while the reduction of adsorbed oxygen was inhibited under inhibitor conditions. The change of functional groups of coal samples was obvious under 20% CaCl2 inhibitor concentration, and the dosage was less than that of 30% inhibitor concentration, revealing the optimal inhibitory effect on coal samples of Zhundong with this concentration. Both ionic liquid inhibitors have obvious effects on the hydrogen bonding content in coal macromolecules, and the effects of both inhibitors on the hydrogen bonding of coal molecules are more obvious in the range of room temperature-50°C, thus inhibiting the coal oxygen reaction. The effect on hydroxyl ether-oxygen hydrogen bonding was the most obvious among the different hydrogen bonds.