Effect of Ionic Liquids with Different Concentrations on Molecular Structure and Combustion Performance of Coal

As a new green chemical inhibitor, ionic liquids can inhibit spontaneous combustion of coal by dissolving and destroying the active structure in coal. In order to investigate the influence of ionic liquids with different concentrations on the molecular structure and the characteristics of low temperature oxidation kinetics of coal at oxygen-poor environment, taking Wucaiwan coal sample in Zhundong mining area as the research object, the molecular structure model of Wucaiwan coal in Zhundong mining area is constructed, and 1-(2-hydroxyethyl)-3-methylimidazole tetrafluoroborate [HOEtMIm] [BF4] ionic liquid is selected. The effect of ionic liquid on coal is investigated from macroscopic and microscopic levels by means of NMR carbon spectroscopy, X-ray photoelectron energy, infrared spectroscopy, thermogravimetry and X-ray diffraction. The results show that different concentrations of [HOEtMIm] [BF4] ionic liquids increase the ignition temperature point and the maximum weight loss rate temperature point of coal samples. The percentage of weight loss in the rapid oxidation stage and the whole combustion process of spontaneous combustion decreases with the increase of ionic liquid concentration. Compared with coal samples treated with other concentrations, the coal samples treated with 15% ionic liquids show good stability, and the fluctuation range of combustion characteristics parameters is small, which shows that high concentration ionic liquids can effectively reduce the influence of temperature on coal samples. Different stages of coal spontaneous combustion oxidation follow different reaction mechanism. The activation energy of the coal samples treated with different concentrations of [HOEtMIm] [BF4] ionic liquids did not change obviously in the evaporation and desorption stages of water, and the flame retardant effect was mainly shown in the oxygen absorption and weight gain stages and thermal decomposition stages. Higher concentration of ionic liquids can make aliphatic, oxygen-containing functional groups and side chains in coal structure fall off , so that the macromolecules of coal are arranged more closely, and the arrangement of organic carbon atoms tends to be oriented and regular gradually. The concentration of ionic liquids changed the polymerization degree of coal macromolecules, and the concentration of ionic liquids was proportional to the polymerization degree of coal macromolecules.