Increased flammability hazard when ionic liquid [C₆mim][Cl] is exposed to high temperatures

Industrial use of ionic liquids may require exposure to high temperatures. We demonstrate that such applications may result in an increase in flammability hazard due to chemical decomposition. The ionic liquid, 1-hexyl-3-methylimidazolium chloride ([C₆mim][Cl]), was selected as the study sample. The flash point and other properties were measured using a commercially available flash point analyzer, a thermogravimetric analyzer (TGA), Fourier transform infrared spectroscopy (FTIR), an integrated TGA-FTIR system, and pyrolysis-gas chromatography-mass spectrometer. We found that thermal decomposition occurred with the release of chloromethane, 1-chlorohexane, 1-hexene, 1-methylimidazole, and 1-hexylimidazole as [C₆mim][Cl] was heated. Such decomposition changed the components of the residual liquid phase. Vaporization of the [C₆mim][Cl] decomposition products increased the mass loss rate on TGA as [C₆mim][Cl] was heated to high temperatures, resulting in a high concentration of flammable gases and a decrease in the flash point, which increased the flammability hazard.