Feasibility of 1-Ethyl-4-butyl-1,2,4-triazolium Acetyl Amino Acid Ionic Liquids as Sustainable Heat-Transfer Fluids

As an improvement on imidazolium amino acid ionic liquids, three ionic liquids, 1-ethyl-4-butyl-1,2,4-triazolium acetylglycine [Taz(2,4)][Acgly], 1-ethyl-4-butyl-1,2,4-triazolium acetylalanine [Taz(2,4)][Acala], and 1-ethyl-4-butyl-1,2,4-triazolium acetylcysteine [Taz(2,4)][Accys], were first synthesized for future application as heat-transfer media. The density, surface tension, isobaric heat capacity, and thermal conductivity were measured in different experimental temperature ranges. Based on the above experimental data, the isobaric thermal expansibility and isentropic and isothermal compressibility, as well as the isochoric heat capacity and heat-storage density, were also calculated. Compared with several popular commercial heat-transfer fluids, it was found that the ionic liquids studied in this work have better performance in terms of heat-storage density of similar to 2.38 MJ.cm(-3).K-1 and thermal conductivity of similar to 0.197 W.m(-1).K-1. In addition, the viscosity was also determined, and the results showed an unexpected reduction by the introduction of a small amount of water for ionic liquids and almost no influence on other thermophysical properties. Finally, we selected a specific heat-transfer process and calculated the heat-transfer coefficient and the heat-transfer area based on the thermophysical properties. Meanwhile, the lower liquid temperature limit (similar to 229 K) and the nontoxic, environmentally friendly anion could provide a wider and safer environment for the application of ionic liquids. Given this, the ionic liquids studied in this work, especially the [Taz(2,4)] [Acgly], could be considered as promising heat-transfer fluid candidates by appropriate adjustment of the water content.