Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

This paper reports the CO2 solubility, density, viscosity, and electrical conductivity for a kind of amino acid ionic liquid (AAIL), tetrabutylphosphonium L-prolinate ([P4444][Pro]). The physical properties of [P4444][Pro] showed the ordinary temperature dependency, i.e. the density and viscosity decreased and the electrical conductivity increased with a temperature rising. One mole of [P4444][Pro] absorbed a 0.970 mol of CO2 at atmospheric pressure of CO2 and 333.2 K, and desorbed only about 17% of the absorbed CO2 at 393.2 K. NMR spectra revealed that a CO2 molecule formed a complex with [Pro] , and [P4444]p had a little effect on the CO2 absorption. The CO2 solubility increased steeply at lower pressures of CO2 less than 0.1 MPa and very gradually in the higher pressure range from 0.1 to 6 MPa at 333.15 K. Other tetrabutylphosphonium AAILs with (S)-2-methylprolinate ([P4444][MePro]) and glycinate ([P4444][Gly]) showed the similar pressure dependencies. The contributions of physical and chemical absorptions to the total CO2 solubility were analyzed to discuss the effect of anion on the high-pressure CO2 solubility. [P4444][Pro] and [P4444][Gly] showed the higher physical and chemical CO2 absorptions (in molarity scale) in the present AAILs, respectively.