Thermal Stability and Decomposition Kinetics of 1-Alkyl-2,3-Dimethylimidazolium Nitrate Ionic Liquids: TGA and DFT Study

The thermal stability and decomposition kinetics analysis of 1-alkyl-2,3-dimethylimidazole nitrate ionic liquids with different alkyl chains (ethyl, butyl, hexyl, octyl and decyl) were investigated by using isothermal and nonisothermal thermogravimetric analysis combined with thermoanalytical kinetics calculations (Kissinger, Friedman and Flynn-Wall-Ozawa) and density functional theory (DFT) calculations. Isothermal experiments were performed in a nitrogen atmosphere at 240, 250, 260 and 270 degrees C. In addition, the nonisothermal experiments were carried out in nitrogen and air atmospheres from 30 to 600 degrees C with heating rates of 5, 10, 15, 20 and 25 degrees C/min. The results of two heating modes, three activation energy calculations and density functional theory calculations consistently showed that the thermal stability of 1-alkyl-2,3-dimethylimidazolium nitrate ionic liquids decreases with the increasing length of the alkyl chain of the substituent on the cation, and then the thermal hazard increases. This study could provide some guidance for the safety design and use of imidazolium nitrate ionic liquids for engineering.

Automated summary

This study investigated the thermal stability and decomposition kinetics of 1-alkyl-2,3-dimethylimidazole nitrate ionic liquids with different alkyl chains, and found that the thermal stability decreases and thermal hazard increases with longer alkyl chains on the cation. These results can provide guidance for the safety design and use of imidazolium nitrate ionic liquids in engineering.