Evaluation of the thermal hazard and pyrolysis mechanism of 1-allyl-3-methylimidazole nitrate and 1-propyl-3-methylimidazole nitrate via thermal analysis and DFT calculation: Effect of structural characteristics

Abstract

Imidazole ionic liquid, as a green solvent, is one of the most widely used ionic liquids. Understanding its thermal safety characteristics and mechanism is the essential basis for its safe application. In this paper, the thermal hazard characteristics of two ionic liquids with typical structural characteristics are systematically studied, which were 1-allyl-3-methylimidazole nitrate and 1-propyl-3-methylimidazole nitrate ionic liquids. The thermal decomposition peculiarities of two ionic liquids were systematically analyzed by thermogravimetric analyzer, differential scanning calorimetry and accelerating rate calorimeter techniques, and the risk of thermal runaway is also evaluated. In addition, the pyrolysis products and microscopic pyrolysis mechanism of ionic liquids were studied via thermogravimetry-Fourier transform infrared spectroscopy, thermogravimetric mass spectrometry and density functional theory calculation, and the essential mechanism of thermal hazard were determined. The influence of substituent structure on the thermal hazard characteristics of imidazole nitrate ionic liquid was preliminarily analyzed from macroscopic experiment and microscopic mechanism two aspects. This study provides a theoretical basis for the safe application, design and development of imidazole nitrate ionic liquids.