Density, viscosity, and CO2 solubility properties of solvents composed of tetrabutylammonium bromide and carboxylic acids

Abstract

Hydrophobic solvent mixtures with low viscosities are promising for industrial gas absorption applications. This study examined the density, viscosity, and CO₂ solubility properties of two hydrophobic solvent mixtures. Mixtures of tetrabutylammonium bromide (TBAB) with hexanoic acid (HA) and octanoic acid (OA) in a molar ratio of 1:3 (denoted as TBAB3HA and TBAB3OA, respectively) were examined. Measurements were performed over the temperature range of 278.15–353.15 K at atmospheric pressure, and high-pressure densities were measured at 298.15, 313.15, and 333.15 K up to 50 MPa. The density and viscosity data were well correlated using a linear equation and the Vogel–Fulcher–Tammann equation, respectively, while the high-pressure densities were described by the Tait equation. Furthermore, the saturated vapor and liquid densities of CO₂, along with its solubility in the TBAB3HA and TBAB3OA systems, were measured at pressures below 8 MPa and at temperatures of 298.15, 313.15, and 333.15 K. The CO₂ solubility was well represented by the Peng–Robinson equation of state. Moreover, a previously developed density-correlation equation was modified to model the pressure–volume–temperature–composition relationship for the CO₂ + TBAB3HA and CO₂ + TBAB3OA systems. This modified equation was further used to determine the partial molar volumes of CO₂ in these solvents, which were analyzed using the Lyckman method to gain insights into CO₂ absorption behavior. Due to their low viscosities and high CO₂ solubilities, TBAB3HA and TBAB3OA are promising candidates for CO₂ capture and storage.