Density and Viscosity Estimation of 1-hexyl-3-methyl Imidazolium Based Ionic Liquids with [BF4] and [PF6] Anions at High Pressures

Abstract

The growing interest in exploring the physical properties of ionic liquids (ILs) could be attributed towards the design of industrial processes based on ILs (nonvolatile) to replace organic solvents (highly volatile). The densities and viscosities of imidazolium based ILs have been measured and reported by a number of researchers at ambient pressure. However, the experimental physical property data for most of the ILs at high pressure is quite scarce due to the difficulties involved in the treatment of natural gas to remove carbon dioxide (CO2) at high pressures. Therefore, there is an immense need to apply correlations and thermodynamic Equation Of State (EOS) models to predict or estimate physical properties. The main objective of this work is to investigate the application of Gardas and Coutinho method and Modified Tait equation to estimate the densities and viscosities of two ILs: 1-hexyl-3-methyl imidazolium tetrafluoroborate; (C6mim) (BF4) and 1-hexyl-3-methyl imidazolium hexafluorophosphate; (C6mim) (PF6) at pressures up to 100 bar and at temperatures (298.15, 308.15, 318.15) K. The results show that these methods could be applied satisfactorily for estimating the density and viscosity of ionic liquids. The densities and viscosities of both ILs increased with the increase in pressure at all the studied temperatures. However, the effect of anion appeared to be significant on both physical properties for the studied ILs and found to be in decreasing order of (PF6) >(BF