Physicochemical Properties and CO2 Solubility of Tetrabutylphosphonium Carboxylate Ionic Liquids

Four tetrabutylphosphonium carboxylate ionic liquids ([P4444][CA]) were prepared, and their densities, viscosities, refractive indices, and conductivities were measured and correlated with thermodynamic and empirical equations in the temperature range of 298.15-348.15 K. The influence of temperature on these four properties of [P4444][CA] was discussed, and their thermal expansion coefficient values were calculated. The CO2 absorption capacity of [P4444][CA] was studied at 313.15 K and 100 kPa. The results indicated that [P4444][Buty] had the highest CO2 capture capacity among these ionic liquids, with an absorption capacity of 0.4 mol·mol-1 and balance time of less than 5 min.