Study on the effect of ionic liquids on coal spontaneous combustion characteristic by microstructure and thermodynamic

Ionic liquids (ILs) including [BMIm][NTf2], [BMIm][BF4] and [HOEtMIm][NTf2] were used to inhibit coal spontaneous combustion (CSC) in this study. The effects of three Ionic liquids (ILs) on the physical and chemical structure of coal including surface morphology, pore structure and functional groups were analyzed by Scanning electron microscope, N2 adsorption, Fourier transform infrared spectroscopy (FTIR). Subsequently, thermodynamic analysis and oxidation kinetics experiment were utilized to investigate the influence of ILs on the oxidation process. Pore structure analyses indicated that ILs could dissolve the minerals in coal, causing the collapse and blocking of pore structure and resulting in lower specific surface area and pore volume of the treated coals by ILs compared to the raw coal (RC). FTIR results showed the enhanced apparent aromaticity and more stable chemical structure of the treated coals, and this increased the difficult of chemical functional group on the coal surface reacting with oxygen. The thermodynamic and oxidation kinetics experiments revealed that ILs delayed the oxidation process of the treated coals obviously, and the treated coals demonstrated less mass loss ratio and oxygen consumption, as well as lower heat release and carbon monoxide products than the RC. Moreover, [HOEtMIm][NTf2] showed the best inhibition effect on coal spontaneous combustion as verified by minimum heat release and highest activation energy Ea for the treated coal sample.