Study on the effect of imidazole ionic liquids on the whole process spontaneous combustion characteristics of long-flame coal based on TG–DSC technology

Abstract

To investigate the influence of imidazole ionic liquids (IILs) on the whole process of coal spontaneous combustion (CSC). Three IILs, [EMIm][BF₄], [BMIm][BF₄], and [BMIm][NO₃], were selected to carry out thermogravimetry and differential scanning calorimetry (TG–DSC) thermal analysis experiments on long-flame coal. The mass change curve (TG) and enthalpy change curve (DSC) of the coal oxidation process were determined. The characteristic temperatures and stages of the whole process of CSC were also divided by TG and DSC curves, respectively. The influence of IILs on the mass and enthalpy changes were analyzed. Then, the inhibition effect of different IILs on the whole process and each stage of CSC were calculated based on the thermal release, and the inhibition strength of anion and cation was discriminated. From the TG curve, the characteristic temperatures (except T₂) and stages of the treated coal moved toward the high-temperature region of the CSC process compared with the raw coal, the whole mass loss behavior lags behind the raw coal significantly, and the mass loss in the combustion stage is smaller than that of the raw coal. From the DSC curve, the characteristic temperatures (except TD₄) of the treated coal are higher than that of the raw coal, and the thermal release at each stage is lower. Although IILs have a slight facilitating on the accelerated oxidation stage of CSC. However, in general, IILs not only inhibit the occurrence and development of CSC mass loss behavior, but also cause the thermal behavior to end earlier and thermal release reduced. The inhibition effect of the three IILs on spontaneous combustion of long-flame coal is as follows: [EMIm][BF₄] > [BMIm][NO₃] > [BMIm][BF₄], with inhibition effects of 26.5%, 19.4%, and 4.8%, respectively. The inhibition effect on CSC of cation [EMIm]⁺ is better than that of [BMIm]⁺, anion [NO₃]^– is better than that of [BF₄]^–, and the inhibition strength of cation was superior to the anion.