Thorough Thermophysical Characterization of the Binary Mixture [P666,14][NTf2] + Ethanol

Abstract

A robust knowledge of the thermophysical and thermochemical properties of mixtures containing ionic liquids is vital to promote the adoption of these chemicals in the recovery of valuable components, such as metallic ions, from waste. In this work, the liquid density, dynamic viscosity, shear stress, torque, electrical conductivity, and refractive index of binary mixtures composed of the phosphonium ionic liquid trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide (usually known as [P_666,14][NTf₂] or [THTDP][NTf₂]) and ethanol were measured at different temperatures and 0.1 MPa. Liquid densities were accurately correlated by the Connors and Wright expression, presenting low standard deviations to experimental data and high determination coefficients (0.999984 < R² < 0.999988), while excess molar volumes were effectively represented by Redlich–Kister expansions (0.9841 < R² < 0.9869). On the other hand, dynamic viscosities were described using an Arrhenius linearization for binary mixtures (0.9611 < R² < 0.9995) and the Vogel–Fulcher–Tammann–Hesse (VFTH) equation for pure components (0.9972 < R² < 0.9975). Furthermore, the ionicity (or degree of dissociation, α) of the ionic liquid was determined using the Walden plot methodology, being practically independent of composition (0.134 < α < 0.191).