Flammability characteristics of ionic liquid 1-Decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Ionic liquids (ILs) are designated as green replacements to so far common used organic solvents because they are under the impression that ILs are both thermal stable and of very low volatility. However, recent studies have indicated that the fire and explosion hazard of ILs should be better understood beyond conventional hazard rating methods. In present work, the fire and explosion hazards of IL 1-Decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) ([C10mim][NTf2]) are investigated by the techniques of auto-ignition temperature tester, simultaneous application of thermogravimetry and differential scanning calorimetry (TGA/DSC), and the combination of thermogravimetric analysis with a Fourier transform infrared spectrometer (TGA-FTIR). The [C10mim][NTf2] exhibits a reverse thermal effect for DSC tests in different gas atmospheres: it exhibits endothermic effect in nitrogen atmosphere, but exhibits exothermic effect in air atmosphere. Part of the heat released in air atmosphere comes from the auto-ignition of heptane in the evolved gas in the DSC tests. The flash point of [C10mim][NTf2] is reported to be 140.2 °C in the literature, which is much lower than the onset temperature of [C10mim][NTf2] in nitrogen atmosphere. Therefore, the decomposition mechanisms of [C10mim][NTf2] in nitrogen atmosphere and in air atmosphere are distinct. The auto-ignition temperature of [C10mim][NTf2] is measured to be of 441°C by the method of ASTM E659-78 (2005a), but this temperature is much higher than the actual temperature at which it could be indeed ignited if sufficient time are allowable for the accumulation of heptane in the evolved gas.