The Viscosity and Density of Ionic Liquid + Tetraglyme Mixtures and the Effect of Tetraglyme on CO2 Solubility

Abstract

We show that the addition of tetraglyme (TG), which is a low viscosity liquid with relatively low vapor pressure, is effective in reducing the viscosity of ionic liquids (ILs). In particular, we measure the viscosities of mixtures of 18 ionic liquids with tetraglyme at temperatures between 278.15 and 323.15 K, with a focus on mixtures that are primarily ionic liquid. Thirteen of the ionic liquids contain aprotic heterocyclic anions (AHA ILs) paired with tetra-alkylphosphonium and imidazolium cations, which we have developed for cofluid vapor compression refrigeration and postcombustion CO2 capture applications. Three bis(trifluoromethylsulfonyl)amide ([Tf2N]−) ionic liquids are included for comparison, as well as trihexyltetradecylphosphonium acetate and trihexyltetradecylphosphonium dicyanamide ([P66614][acetate] and [P66614][DCA]). In addition, we present the densities of trihexyltetradecylphosphonium 1,2,3-triazolide ([P66614][3-Triz]) + tetraglyme mixtures at temperatures between 283.15 and 353.15 K. Finally, we show that the solubility of CO2 in mixtures of [P66614][3-Triz] + 30 mol % tetraglyme and trihexyltetradecylphosphonium 1,2,4-triazolide ([P66614][4-Triz]) + 30 mol % tetraglyme at 313.15, 333.5, and 353.6 K and pressures to 34 bar can be represented reasonably well by a mole fraction weighted sum of the solubilities (on a mole ratio basis) in the two pure components.