Effect of Ionic Liquids on Low-Temperature Oxidation of Coal

Three 1-butyl-3-methyl imidazolium ([BMIm]+) based ionic liquids (ILs) with different anions, including tetrafluoroborate ([BF4]−), acetate ([Ac]−), and trifluoromethane sulfonate ([OTf]−), were selected to investigate the inhibition effect of ILs on low-temperature oxidation of coal by oxidizing raw coal and ILs-treated coals under air during 20–180°C. The coal structure was characterized by Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The Raman results show that the ILs treatment can inhibit the low-temperature oxidation activity of disorder structure in coal. The FTIR results demonstrate that the ILs can break and dissolve the associated hydrogen bonds and methylene groups, so that the low-temperature oxidation activity of ILs-treated coal is inhibited. The analysis on oxygen consumption and index gases of coals by gas chromatograph further confirms the spectra results that ILs treatment can inhibit the low-temperature oxidation of coal. The inhibition effect is in the order of [BMIm][OTf] > [BMIm][BF4] > [BMIm][Ac].