Estimation of mixture viscosity of ionic liquids using cubic two state equation of state and Eyring theory

Abstract

In this work the Cubic two State (CTS) equation of state (EoS) has been utilized to model the pure and mixed ionic liquids (ILs) viscosity. The free volume theory (FVT) and Eyring theory have been coupled with the CTS EoS to estimate the pure and mixture IL viscosity. The average relative deviation (ARD%) of pure imidazolium-based ILs viscosity has been obtained 0.42 %. The results show that the CTS+FVT can estimate the pure viscosity of ILs up to high pressure accurately. The mixture viscosity has been calculated using the CTS coupled with the Eyring theory and Redlich-Kister mixing rule. In this regard, four adjustable parameters of the thermal contribution of excess activation free energy in the Redlich-Kister mixing rule have been adjusted using the experimental viscosity data. The average ARD% value of mixture viscosity has been obtained 3.6 %. The effect of ideal, thermal, and mechanical contributions of excess Gibbs free energy of the Eyring theory on mixture viscosity has been studied. The results show that the thermal and mechanical terms have a minor effect on mixture viscosity. The CTS model results have been compared to the SAFT-VR Morse EoS. The result shows that a simple and robust model like CTS can be utilized as an alternative model for complex SAFT-based models to estimate the pure and mixture viscosity of IL-containing systems.