Relationship between flash point of ionic liquids and their thermal decomposition

Abstract

Recently, ionic liquids were verified to be combustible instead of nonflammable; the contrary was thought to be true due their extremely low vapor pressure. Flash point is one of the most important variables used to characterize the fire and explosion hazards of liquids. Because of extremely low vapor pressure and decomposition at elevated temperatures, the reason for ionic liquids to be combustible should be different from that of traditionally defined liquids. The flash point of ionic liquids in relation to their decomposition was investigated in this study by the estimation of vapor pressure and by use of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and flash point analyzer apparatus. The ionic liquids 1-ethyl-3-methylimidazolium ethylsulfate () and 1-butyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][NTf 2 ]), were selected as test examples. Results revealed that the flammability of ionic liquids was mainly attributed to the decomposition of the ionic liquids generating flammable substances instead of themselves vaporizing, as do traditionally defined combustible/flammable liquids. Lyon's method, applied by Fox et al. to estimate the flash point of ionic liquids from the TGA decomposition temperature, was assessed using our experimental data and the data from the published literature and resulted in substantial overestimation of the flash-point values of ionic liquids, which underestimates the fire and explosion hazards of ionic liquids. This deviation is attributed to flash-point values of ionic liquids located in the second temperature range of the TGA tracing, rather than in the third analogue, as predicted by Lyon's method.

An Insight of Combustibility Induced Safety Issues Pertaining to Ionic Liquids

“…These examples show again that the traditional flashpoint type tests are certainly not adequate in most cases to properly characterize the fire hazard, as reported by Liaw et al [18]. This is related to our findings that ILs do not behave as traditional flammable liquids where the fire results from the combustion of the vapor phase of the concerned chemical.…”

Synthesis of D-pantolactone via Combined a Novel Organocatalyst Catalyzed Asymmetric Aldol Reaction and Hydrogenation Catalyzed by Cu-/SiO<sub>2</sub>

“…The reaction mixture was heated at room temperature under magnetic stirring for 24 h. After evaporating solvent, the buff precipitate was added a mixed solution containing 60 mL of acetonitrile and 10 mL methanol at room temperature under vigorous magnetic stirring for 2 h. The solid was filtered and evaporated to remove the unreacted L-histidine and solvent, dried in vacuum at 353 K for 24 …”

“…In nature, small organic molecules, in particular amino acids [11][12][13] and their derivatives [14][15][16][17], are rich chiral sources, which are used as the catalysts, but with recycling problems, such as extensive work-up procedures with the corresponding waste generation or more time to recover the catalyst between two cycles [18][19][20]. However ionic liquids (ILs) have been widely used as environmentally benign solvents to replace common organic media [21] with advantages of reusable, strong design ability, low pollution, low toxicity, and excellent miscibility with organic compounds [22][23][24]. Because of the above-mentioned highly tunable characteristics (broad cation/anion combinations) and the enhancement of reaction efficiency by using ILs as solvents [25][26], ILs have gained wide recognition in specific engineering, especially as catalysts to catalyze aldol reactions [27][28].…”

Combustion Characteristics of an Ammonium-Dinitramide-Based Ionic Liquid Propellant

“…However, some papers reported that certain ILs can burn. 6) Although thermal decomposition and measurement of flash point were researched with respect to ILs, 7,8) the combustion mechanism of ILs has not yet been determined.…”