Water-Ionic Liquid Working Fluids in Absorption Cycles: Fluid Screening, Vapor-Liquid Equilibrium Measurements and Modeling, and Performance Evaluation

Absorption chiller represents a technology that facilitates the recuperation of low-grade thermal energy. However, commonly used working fluids, such as water/lithium bromide (LiBr) and ammonia/water, exhibit several drawbacks, including issues related to corrosion, crystallization, toxicity, and explosiveness in the case of ammonia. Water/ionic liquids (ILs) are considered promising alternative working fluids due to their high efficiency. In this study, we initially employed the COSMO-SAC model to screen potential IL-water working pairs, considering numerous ILs, which encompassed 35 different anions and 18 cations. Three ILs with promising water absorption capacities were identified: 1-butyl-3-methylimidazole chloride ([Bmim][Cl]), 1-butyl-3-methylimidazole thiocyanate ([Bmim][SCN]), and 1-hexyl-3-methylimidazole chloride ([Hmim][Cl]). Subsequently, we measured the vapor-liquid equilibrium (VLE) data of water + [Bmim][Cl], + [Bmim][SCN], and + [Hmim][Cl] mixtures over a temperature range of 313.15 to 363.15 K, with IL mole fractions ranging from 0.15 to 0.50. The binary interaction parameters of the NRTL and e-NRTL models were fitted to the new data. Finally, we evaluated the coefficients of performance (COP) of the investigated working pairs in an absorption cycle. The predicted COP for the water + [Hmim][Cl] pair is found to be slightly better than that of the water + LiBr pair.