Thermophysical properties of choline and pyridinium based ionic liquids as advanced materials for energy applications

Abstract

Phase transitions, isobaric heat capacities and thermal stability of four ionic liquids (ILs) are determined in this work. The selected Ionic Liquids (ILs) have two different cations, pyridinium and choline, and they are combined with three different anions, acetate, dihydrogen phosphate and tosylate. Solid-solid and solid-liquid phase transitions and isobaric molar heat capacities are determined using two calorimeters, both based on the differential scanning calorimetry methodology. Thermal stability of the studied compounds is analysed through the thermogravimetric technique (TGA). Degradation temperatures are obtained from TGA experiments using the dynamic method, whereas isothermal TGA is used to determine the maximum operation temperature. The results show that, all the ILs present crystalline behaviour, with melting temperatures within the interval of 88 °C and 123 °C, whereas heat capacities linearly increases with temperature. A clear dependence with the anion is observed for both heat capacities and thermal stability, being ILs with the tosylate anion those presenting the highest values of molar heat capacities and the highest thermal stability.