Assessment of vapor-liquid equilibrium models for ionic liquids based absorption systems

Absorption refrigeration and heat pump cycles, especially for the promising double-effect absorption heat pump systems, are drawing considerable attention because they can make effective use of higher temperature heat from concentrated solar energy and exhaust gases. Ionic liquids (ILs), novel and tailor-made absorbents, can be used with natural refrigerants as working pairs for absorption refrigeration cycles. This paper presents a preliminary work to select an appropriate model (from equation of state (EOS) or activity coefficient-based methods) to describe the vapour-liquid equilibrium properties of the binary systems between natural refrigerants and ILs. First, different thermodynamic models are reviewed. Then, some experimental vapour-liquid-equilibrium data from literature of ILs based mixtures are fitted with different models (Redlich-Kwong EOS with mixing rule, NRTL and UNIFAC models). The fitted interaction parameters and fitting quality of each model are listed for comparison. Finally, the applicability of each model is estimated by taking into account both its precision and its simplicity.