Fire and explosion hazards of ionic liquid 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide

Abstract

Low volatility materials that do not emit sufficient vapor to form a combustible mixture with air, under temperate conditions, are considered a lower fire hazard than materials with higher volatility. Because ionic liquids have very low volatility, they are widely considered to be green alternatives to organic solvents and have long been considered nonflammable. However, recent research has indicated some ionic liquids are flammable because of the auto-ignition of their thermal decomposition products rather than the combustion of the vapors itself. Ionic liquid 1-methyl-1-propylpyrrolidine bis(trifluoromethanesulfonyl)imide has been reported to be an electrolyte base candidate for lithium batteries, and many electrochemical characteristics of this ionic liquid have been extensively investigated. Characteristics about its fire and explosion hazards, however, are still not reported in the literature. It is obvious that such information is indispensable to safely use this ionic liquid.In this study, the fire and explosion hazards of ionic liquid 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide are investigated via auto-ignition tester, TGA/DSC and TGA-FTIR. It is found that the auto-ignition temperature of this ionic liquid is 441 °C with the ignition delay time of 38.2 s. The decomposition process of this ionic liquid is found to be endothermic in the nitrogen atmosphere, but it is exothermic in the air atmosphere. Further TGA/DSC experiments indicate that in the air atmosphere the amount of heat release will increase as the reaction gas purge rate increases, but in the nitrogen atmosphere the amount of heat absorbed is independent of the reaction gas purge rate. It is also found from TGA-FTIR experiments that in the air atmosphere the concentration of carbon dioxide in the evolved gas was much higher than that in the nitrogen atmosphere. Moreover, carbon monoxide is observed in the air atmosphere, but is not observed in the nitrogen atmosphere. If in the air atmosphere the spontaneous combustion of the gas-phase decomposition products occurs, aforementioned observations can be reasonably explained.