New Method for the Estimation of Viscosity of Pure and Mixtures of Ionic Liquids Based on the UNIFAC–VISCO Model

Nan Zhao,Johan Jacquemin,Volkan Degirmenci,Ryan Oozeerally

doi:10.1021/acs.jced.6b00161

Abstract

A modified UNIFAC–VISCO group contribution method was developed for the correlation and prediction of viscosity of ionic liquids as a function of temperature at 0.1 MPa. In this original approach, cations and anions were regarded as peculiar molecular groups. The significance of this approach comes from the ability to calculate the viscosity of mixtures of ionic liquids as well as pure ionic liquids. Binary interaction parameters for selected cations and anions were determined by fitting the experimental viscosity data available in literature for selected ionic liquids. The temperature dependence on the viscosity of the cations and anions were fitted to a Vogel–Fulcher–Tamman behavior. Binary interaction parameters and VFT type fitting parameters were then used to determine the viscosity of pure and mixtures of ionic liquids with different combinations of cations and anions to ensure the validity of the prediction method. Consequently, the viscosities of binary ionic liquid mixtures were then calculated by using this prediction method. In this work, the viscosity data of pure ionic liquids and of binary mixtures of ionic liquids are successfully calculated from 293.15 K to 363.15 K at 0.1 MPa. All calculated viscosity data showed excellent agreement with experimental data with a relative absolute average deviation lower than 1.7%.

Highlights

Ionic liquids (ILs) with negligible vapor pressure at ambient temperature and pressure have made them potential greener alternatives to current solvents
We developed a methodology based on the UNIFAC−VISCO group contribution model to determine the viscosity of ILs as a function of the temperature from 293.15 to 363.15 K at 0.1 MPa
We report the successful development of this method for the prediction of viscosity of pure ILs and their mixtures as the function of the IL structure, composition, and temperature at 0.1 MPa

Summary

Introduction

Ionic liquids (ILs) with negligible vapor pressure at ambient temperature and pressure have made them potential greener alternatives to current solvents. Recent advances have been focused on developing new ILs for use in chemical synthesis, catalysis, and fuel cells.[1] ILs are composed of cations and anions; where the cations are typically bulky, asymmetrical, and organic.[2,3] the corresponding anions can be either organic or inorganic.[4] The specific chemical and physical properties exhibited by an IL are determined by its particular cation−anion combination. It is theoretically possible to tailor an IL to possess a certain desired set of physical properties by altering its constituent cation−anion pair,[5] which are often referred to task-specific ILs.[6,7]

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Conclusion