Evaluation of thermal decomposition characteristics and potential hazards of 1-n-butyl-3-methylimidazolium dicyanamide by STA, ARC, and TG-FTIR

As a new solvent with a broad prospect, ionic liquids (ILs) are widely used in catalysis, organic synthesis, and electrochemistry due to their peculiar physical and chemical properties. Nonetheless, their safety issues are often overlooked. This paper aims to decode the thermal reaction and decomposition hazard characteristics of ILs with an innovative method. Initially, the results of the thermal stability study of 1-n-butyl-3-methylimidazolium dicyanamide ([BMIM]DCN) using non-isothermal thermogravimetric and adiabatic analysis show that the decomposition process of [BMIM]DCN can be divided into three stages. By employing the Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods, the apparent activation energy of decomposition was calculated and the stability of [BMIM]DCN was compared with structure-similar ILs (with the same imidazole cation). To predict the mechanism of [BMIM]DCN decomposition in the early stage, the products of the [BMIM]DCN under temperature-programmed conditions were analyzed by TG-FTIR, and a huge amount of toxic gases were detected in its decomposition products. In adiabatic tests, there is a sharp increase in pressure at about 382 degrees C, and the pressure of the system increases by about 12 times within 0.2 s. Furthermore, product analysis results show that the danger of the thermal decomposition of [BMIM]DCN is mainly due to the rapid pressure rise and toxicity caused by the massive gas products, such as HCN and NH3. The findings of this study can be used to develop thermal stability prediction models for similar ILs and provide the necessary foundation for the design and selection of precise processing methods and appropriate safety systems.