Fire and explosion hazards of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Abstract

Ionic liquids (ILs) have very low volatility and are consequently considered as a green replacement to the organic solvents that have been widely used to date. The fire and explosion hazards of traditional organic solvents primarily depend on the combustibility of their vapors; therefore, ILs have been regarded as nonflammable for a long time because of their low volatility. However, recent studies have shown that ILs are flammable due to their thermal stability and consequently, the fire and explosion hazards of ILs limit their practical applications. The compound 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (abbreviated as [EMIM][Tf₂N]) has been considered a potential candidate solvent for surfactant systems, but studies about the fire and explosion hazards of this IL are rare in the literature. In this study, the fire and explosion hazards of [EMIM][Tf₂N] were explored in terms of different aspects. The auto-ignition temperature of [EMIM][Tf₂N] was found to be 478 °C with an ignition delay time of 12.6 s. It was observed with the TGA/DSC system that the decomposition of [EMIM][Tf₂N] was endothermic in a nitrogen atmosphere but exothermic in an air atmosphere. The dynamic TGA curves showed that the apparent activation energies were the same in both nitrogen and air atmospheres, but the dynamic DSC curves showed that the apparent activation energies were different in nitrogen and air atmospheres. The apparent activation energy inferred from the DSC curve in an air atmosphere was found to be the same as the apparent activation energy estimated by the Semenov theory of thermal ignition. Analysis of the gaseous decomposition products of [EMIM][Tf₂N] by the TGA-FTIR system indicated that the exothermal effect in the air atmosphere was caused by the auto-ignition of acetylene (which is one of the gaseous decomposition products) and not by decomposition itself.