Oxidative stability, thermal hazard analysis, and decomposition kinetics of 1-methylimidazolium nitrate via DSC, TGA, and GC/MS

Abstract

Imidazolium-based ionic liquids are green solvents used as separation and electrolyte media in liquid–liquid extraction processes and electrochemical devices. However, they are volatile and flammable once they reach their thermal decomposition temperatures. In the present study, the oxidative stability, decomposition, and combustion reaction of 1-methylimidazolium nitrate [Mim][NO3] were investigated via thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). TG analysis revealed a single-stage mass loss between 117.6 and 230.2 °C with oxidative onset temperatures in the range of 126.6–163.2 °C with the increase in heating rate (1.0, 2.0, 4.0, and 8.0 °C min−1). DSC results indicated the degradation as exothermic with the average enthalpy of decomposition as 1610.4 J g−1. The estimated average value of apparent activation energy using isoconversional methods such as Kissinger, FWO, and Friedman was in the range of 106.1–114.2 kJ mol−1, and the reaction function (autocatalytic model) is expressed as: f(α) = (1 − α)1.42 (0.017 + α0.62) using multivariate nonlinear regression. The GC/MS analysis revealed the formation of methane isocyanate indicating the hazardous, toxic, corrosive, and carcinogenic nature of the decomposed gases. This research was aimed to develop a predictive model for oxidative degradation behavior and to provide the necessary basis for the design of precise safety systems.