Density, viscosity, and CO2 solubility of deep eutectic solvents comprising tetrabutylammonium or phosphonium bromide and ethylene glycol

The densities and viscosities of deep eutectic solvents (DESs) consisting of binary mixtures of tetrabutylammonium bromide (TBAB)/ethylene glycol (EG) or tetrabutylphosphonium bromide (TBPB)/EG in a 1:3 molar ratio (denoted as TBAB3EG or TBPB3EG) were measured over a temperature range of 273.15-363.15 K under atmospheric pressure. Their high-pressure densities up to 50 MPa were also measured at 298.15, 313.15, and 333.15 K. The densities and viscosities of TBAB3EG and TBPB3EG were correlated using linear and VogelFulcher-Tammann equations. High-pressure densities were expressed using Tait equation. The saturated vapor and liquid densities in CO2 + TBAB3EG and CO2 + TBPB3EG and the CO2 solubilities in TBAB3EG or TBPB3EG were measured at pressures up to 13 MPa and temperatures of 298.15, 313.15, and 333.15 K. The CO2 solubilities in TBAB3EG or TBPB3EG were correlated using the Peng-Robinson equation of state. The densitycorrelated equation previously proposed by the authors was used to express the pressure-volume-temperaturecomposition (pvTx) relationship based on the data measured for the CO2 + TBAB3EG and CO2 + TBPB3EG systems. Next, the density-correlated equation was employed to determine the partial molar volume. The partial molar volumes of CO2 in various DESs were compared with those of ionic liquids and other liquids using the method described by Lyckman et al. (1965).