Dielectric properties and kinetic analysis of nonisothermal decomposition of ionic liquids derived from organic acid

Abstract

Dielectric relaxation spectra of three representatives of the class of hydroxyethylammonium carboxylate protic ionic liquids (PILs), namely 2-hydroxyethylammonium formate [2-HEAF], 2-hydroxyethylammonium propionate [2-HEAP] and 2-hydroxyethylammonium butanoate [2-HEAB], were recorded over a wide frequency range (0.05 ≤ ν(GHz) ≤ 50) at 25 °C. The thermal decomposition kinetics of these ionic liquids derived from organic acids was studied by thermogravimetry (TG) using nonisothermal experiments. For the purpose of kinetic analysis, the thermal behavior of the samples was studied in the temperature interval from ambient temperature up to 420 °C at different heating rates (5, 10, 15 and 20 °C min−1). Isoconversional kinetic analysis was performed using Friedman’s (FR) differential method and the integral Kissinger–Akahira–Sunose (KAS) method. The dependence of the apparent activation energy (E) on the conversion fraction (α) for the investigated decomposition processes was analyzed. It was found that the molecular structure of the involved anion significantly influences the dielectric properties of the studied PILs. It was also established that a change in the anion structure drastically affects the shape of the thermo-analytical curves. Among the considered PILs [2-HEAF] has the highest thermal stability. However, considering kinetic properties, certain deviations were observed and referred to hydrogen bonding development and steric impediment effects.