Testing inhibitory effects of a panel of ionic liquids on differing phases of coal spontaneous combustion

Abstract

Coal spontaneous combustion (CSC) is a major safety concern affecting not just miners and businesses, but of industry in China generally. Chemical methods are already widely applied in the field of CSC prevention and plays a vital role in suppressing its negative effects. Ionic liquids (ILs) are novel and environmentally friendly solvents that have shown possible inhibitory effects on CSC through controlling the reactive groups in coal’s molecular structure. To study the effects of various ILs on CSC more thoroughly, this paper examined several types of IL that had been pre-treated for different periods and examined how they performed during different phases of the combustion process. A long flame coal type was selected and immersed in four ILs [BMIM][BF4], [BMIM][NO3], [BMIM][I], and [EMIM][BF4]. Immersion periods were 2 days, 3 months, and 6 months; a raw coal sample was retained as a control. LFA 457 laser-flash apparatus determined the thermophysical properties of the samples between 30 and 300 °C. The kinetic process of the samples (30–800 °C) was deduced by thermogravimetric–differential scanning calorimetry thermal at various heating rates (2, 5, 10, and 15 °C min−1), and the thermal effect parameters were obtained. Results from this paper show that immersion treatment using ILs has an inhibitory effect on CSC, and the reliability of the thermophysical parameters was verified by uncertainty analysis. The pre-treated samples characteristics and exothermic peak temperature with different degrees of hysteresis were recorded, and statistical analysis verified the conclusions from the thermal physics experiments. The pre-treated sample with the greatest lag over various stages was found, and the apparent activation energy (Ea) of its rapid oxidation stage was calculated by Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods. Meanwhile, the two kinetic methods confirm each other and come to a conclusion after joint verification. The greatest Ea found here was for a 6-month immersion coal sample using the IL [BMIM][BF4].