Thermodynamic properties and corrosivity of water+ imidazolium-based ionic liquids as new working pairs for absorption heat transformer cycle

Imidazolium-based ionic liquids exhibit significant potential as working fluids in absorption heat transformers, owing to their superior solubility and thermal stability. In this study, the corrosion rates of nine imidazolium-based ionic liquids, with mass concentrations ranging from 30% to 70%, were systematically evaluated. Based on these corrosion rate evaluations, further thermodynamic assessments were conducted on four key working pairs, namely [EMIM][MeSO 3 ]+H 2 O, [EMIM][Ac]+H 2 O, [EMIM]Cl+H 2 O, and [EMIM][DEP]+H 2 O, involving parameters including density, viscosity, specific heat capacity, and thermal stability. Polynomial fitting was applied using the least squares method. The results showed that the density, viscosity and specific heat capacity of these four working pairs were in the range of 0.98-1.18 g·cm −3 , 0.5-15.5 mPa·s and 2.3-4.0 J·g −1 ·°C −1 , respectively. Furthermore, all four ILs presented a significant thermal stability below 250°C, further confirming their suitability for heat pump technology. Among these four working pairs, both [EMIM][MeSO 3 ]+H 2 O and [EMIM]Cl+H 2 O exhibited lower viscosities and specific heat capacities. However, it should be noted that [EMIM][MeSO 3 ]+H 2 O demonstrated a substantially higher corrosion rate (reaching up to 734.84 μm∙y −1 ), making [EMIM]Cl+H 2 O the preferable option for most absorption transformers. This study establishes an experimental basis for the feasibility of the application of ionic liquids in absorption heat transformer cycle and provides data to support the selection of cleaning working pairs.