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

• Published in: Journal of hazardous materials 2019-04, Vol.367, p.407-417
• Main Authors: Liaw, Horng-Jang, Liou, Yuan-Ruei, Liu, Ping-Hui, Chen, Hao-Ying, Shu, Chi-Min
• Format: Article
• Language: English
• Subjects: 1-Hexyl-3-methylimidazolium chloride; Decomposition; Flammability; Flash point; Ionic liquids
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2018.12.086

•The flammability hazard of ILs is attributed to decomposition of ILs rather than their vaporization.•The flammability hazard of ILs increased when they were exposed to high temperatures.•The flammability hazard increase of ILs is due to the conversion of the IL to volatile organic products. 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.