Effects on the activities of coal microstructure and oxidation treated by imidazolium-based ionic liquids

To study the effect of ionic liquids (ILs) of the microstructure on the surface of the coal, four ILs ([Emim][BF4], [Bmim][BF4], [Bmim][NO3], and [Bmim][I]) were selected to treat the coal samples. Fourier transform infrared spectroscopy and synchronous thermal analyzer were employed to conduct the experimental tests. Active functional groups were analyzed when the ILs contained the same anion or cation. The results indicated that the quantity of the hydrocarbyls and the oxygen-containing functional groups for the coal sample treated by [Emim][BF4] was significantly less than the three coal samples by other ILs treated, in which the maximum area ratio of the hydrocarbons and the oxygen-containing functional groups was 0.553 and 1.159, respectively. However, ILs had lesser destructive effects on the aromatic hydrocarbons. The ILs containing [Emim](+) shared stronger destructibility to the coal's micro-active structure than that containing [Bmim](+). The highest impact was the hydrocarbyl of the coal. While including the same [Bmim](+), the extent of destruction to the hydrocarbyls and the oxygen-containing functional groups of coal was varied in descending order as [NO3](-) > [I](-) > [BF4](-). The aliphatic hydrocarbons were destroyed by the anion of ILs following the order: [I](-) > [BF4](-) > [NO3](-). During the low-temperature oxidation stage, the apparent activation energy increased, whereas the reactivity of coal samples by ILs treated decreased in the order: [Bmim][NO3] < [Bmim][I] < [Bmim][BF4] < [Emim][BF4].