PHASE-EQUILIBRIA FOR CARBON-DIOXIDE ETHANOL-WATER SYSTEM AT ELEVATED PRESSURES

For applications related to the use of supercritical CO2 to concentrate ethanol solutions from a fermentation broth, vapor-liquid equilibria for the CO2-C2H5OH and the CO2-C2H5OH-H2O system were measured at 313.2, 323.2, 333.2, and 343.2 K at pressures up to 18.5 MPa over a wide range of ethanol concentration. A circulation type of equilibrium apparatus in which both vapor and liquid phases were continuously recirculated was adopted for measurements. Using CO2, aqueous ethanol can be concentrated above atmospheric azeotropic composition (89.4 mol %) when the pressure in the ternary system CO2-C2H5OH-H2O is below the critical pressure of the binary system CO2-C2H5OH. The experimental measurements for the phase equilibria were compared with the results predicted by Patel-Teja equation of state using each one of the four types of mixing rules: conventional, Wilson, Yu et al., and Adachi and Sugie. Good estimation was obtained for the phase equilibria of the binary systems except for the conventional mixing rule. It was also found that the phase behavior of the ternary system can be better predicted by the Patel-Teja equation of state with the Adachi and Sugie mixing rule than with the three other mixing rules, though the concentration is not estimated satisfactorily.