A modified UNIQUAC model for calculating phase-equilibrium of ionic liquid containing systems

Since ionic liquids are increasingly employed as separation media in separation technologies, the development of thermodynamic model for design and optimization of the corresponding separation operations is very urgent. At present, the widely used thermodynamic models treat ionic liquid as a non-electrolyte or strong electrolyte. Although the calculation results are close to the experimental results, the treatment of ionic liquid does not consistent with the physical fact that ionic liquids ionize in solution, even in pure ionic liquid. In this work, we proposed a modified model for the calculation of the phase behavior of ionic liquid containing systems. The model combines a term of the modified Debye-Hückel type with a UNIQUAC equation and treats ionic liquid as a weak electrolyte, using an empirical expression to describe the ionization of ionic liquid. The new model has been utilized to correlate the vapor-liquid equilibrium, liquid-liquid equilibrium, solid-liquid equilibrium data as well as infinite dilution activity coefficient for ionic liquid containing systems with high accuracy. Besides, the model can be used to quantitatively describe the ionization behavior of ionic liquid.