Flammability estimation of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Ionic liquids (ILs) are known as room temperature molten salts, which are considered green replacement to traditional organic solvents. The fire hazards of traditional organic solvents mainly depend on the combustibility of their vapors, thus ILs are generally regarded as nonflammable owing to their low volatility. However, recent studies show that ILs may combust due to the potential hazards of thermal decomposition, indicating the issue of fire and explosion of ILs are eager to be evaluated during the applications. In this study, the fire and explosion hazards of IL 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C6mim][NTf2]) are explored in different aspects. The traditional definition of the flammability for the common organic solvent is not thoroughly applicable to [C6mim][NTf2] due to the low volatility. Furthermore, the common definition of reactivity for traditional organic solvents also fails to apply, because the decomposition reaction is indeed an endothermic reaction. However, the auto-ignition of some decomposition products will result in fire and explosion hazards for [C6mim][NTf2]. Therefore the application of such data in safety purposes should be very careful. •The auto-ignition temperature of [C6mim][NTf2] was measured.•The heat releases were different under air and nitrogen atmosphere.•The endothermic under nitrogen atmosphere was caused by the thermal decomposition.•The exothermic under air atmosphere was caused by the spontaneous ignition.