Effects of 1-butyl-3-methylimidazolium tetrafluoroborate and the oxygen concentration on the spontaneous combustion of coal

Ionic liquids (ILs) are a type of environmentally friendly solvents. Several studies have proven that ILs can inhibit the spontaneous combustion of coal (SCC). In this study, a synchronous thermal analyzer was used to analyze the effects of the imidazolium-based IL [BMIM][BF4] on coal of three metamorphic grades. A coal sample exhibiting the optimal inhibiting result was selected to investigate the effect of the oxygen concentration on IL inhibition. The results revealed that the influence of IL on the mass loss process of the three metamorphic grades of coal varied considerably. High inhibition was observed in lignite. However, the IL promoted the mass loss process in 1/3 coking coal and anthracite. The IL delayed the ignition temperature of lignite by 42 degrees C, whereas those of 1/3 coking coal and anthracite were advanced by 10 and 8 degrees C, respectively. Furthermore, the initial exothermic temperature of the three treated coal samples was higher than those of the raw coal samples. Compared with the raw coal samples, the heat released per gram of lignite, 1/3 coking coal, and anthracite was reduced by 1142, 353, and 226 J, respectively. The results indicated that the IL had a prominent inhibiting effect on the exothermic properties of the three coal samples, and the inhibiting effect decreased with an increase in the metamorphic grade of coal. Moreover, the oxygen concentration did not alter the inhibition properties of the IL on the SCC. However, the inhibiting effect weakened as the oxygen concentration decreased.