Ion exchange synthesis and thermal characteristics of some [N+4444] based ionic liquids

Eight salts, derived from tetrabutylammonium cation [N+4444] and inorganic anions like BF4−, NO3−, NO2−, SCN−, BrO3−, IO3−, PF6− and HCO3− were synthesized using the ion exchange method. These ionic liquids (ILs) were characterized using thermogravimetry, differential scanning calorimetry and infrared spectroscopy. Thermophysical properties such as density, volume expansion, heat of fusion, heat of solid–solid transitions, specific heat capacity and thermal energy storage capacity were determined. The total of heat of solid–solid transitions observed below the melting points exceeded the heat of fusion in some cases. The thermal conductivity of the samples was determined both in solid and liquid phases. High values of thermal energy storage capacity and handsome liquid phase thermal conductivities made many of the ionic liquids under investigation were recommended as Thermal Energy Storage Devices (TESDs) as well as heat transfer fluids.

► Ionic liquids are promising thermal energy storage and heat transfer devices.
► [N+4444] based ILs find applications in the temperature range of −50 to 150 °C.
► [N+4444] based ILs show multiple phase transitions in the DSC.