Phase Equilibrium Study of the Separation of Ethanol–Water Solution with Supercritical CO₂

Abstract

To provide a better theoretical basis for obtaining higher concentration of ethanol from a fermentation broth using near- or super-critical CO₂ extraction, the vapor–liquid equilibria for the quaternary system of CO₂, ethanol, water and an entratner were measured at 35.0°C and 10 MPa for various entrainer concentrations. Experiments were carried out for four entrainers: glycerol, ethylene glycol, 1,3-propanediol and propylene glycol. The experimental results demonstrated that the upper limit of ethanol composition for the CO₂–ethanol–water ternary system could be raised by the addition of the above entrainers other than propylene glycol. It was also found that this effect of the entrainer could be estimated qualitatively from its solubility parameter value. The group parameter values of the GC-EOS by Jorgensen were redetermined using binary vapor–liquid equilibrium (VLE) data in order to improve the accuracy of prediction of the VLE of the CO₂–ethanol–water and the CO₂–ethanol–water-entrainer mixtures.