Effects of imidazole ionic liquid on macroparameters and microstructure of bituminous coal during low-temperature oxidation

The effects of ionic liquids (ILs) on the macrostructures and characteristic parameters of coal samples during low-temperature oxidation (30.0-200.0 degrees C) were investigated. The Fourier transform infrared (FTIR) spectroscopy results clearly illustrated that the destruction of functional groups in the coal molecular structure was prominent, and that the benzene rings in the coal molecular structure were barely affected. Therefore, it can be inferred that ILs played a primary role in the destruction of functional groups in the side chain of the coal molecular structure; thus, the aromatic ring was barely affected. Moreover, the inhibition of the functional group at high temperatures by the ILs was also barely effective. The analysis results of the temperature-programmed testing system indicated that the CO concentration and the production rate of CO by coal samples treated with the ILs presented decreasing trends. This result was in sound agreement with the FTIR results for the quantity of carbonyl groups in oxidation stage. The oxygen consumption rate of the sample treated with the ILs gradually decreased beyond the cracking temperature. Moreover, the difference between the thermal release intensity of coal samples treated with the ILs and that of raw coal gradually increased beyond the critical temperature. The inhibiting effect of [Bmim] [BF4] appeared to be greater than that of other ILs, and [Bmim] [I] and [Emim] [BF4] exerted a slight influence on the low-temperature oxidation process of coal samples. Therefore, we conducted a comprehensive comparison of the inhibiting effect of four ILs on bituminous coal during low-temperature oxidation and found that the ILs can be listed in the following order on the basis of their inhibiting effect: [Bmim] [BF4] > [Bmim] [NO3] > [Emim] [BF4] > [Bmim] [I].