Excess molar enthalpies for mixtures of supercritical CO2 and ethyl acetate and their role in supercritical fluid applications

Abstract

Mixtures of supercritical CO2 and ethyl acetate (EA) are very often involved in supercritical fluid applications and their thermodynamic properties are required to understand and design these processes. Excess molar enthalpies (HmE) for (CO2+EA) mixtures were measured using an isothermal high-pressure flow calorimeter under conditions of temperature and pressure typically used in supercritical processes: pressures from (9.00 to 18.00)MPa and temperatures from (313.15 to 333.15)K. Mixtures showed exothermic mixing; excess molar enthalpies exhibited a minimum in the CO2-rich region. The effects of pressure and temperature on the excess molar enthalpy of (CO2+EA) are large. The most exothermic HmE values were observed for a coincident CO2 mole fraction value of 0.737 at T/K=(323.15 and 333.15) and P/MPa=9.00: (−4489 and −4407)J·mol−1, respectively. Two-phase splitting was observed in the CO2-rich region at T/K=333.15 and P/MPa=9.00; in this region HmE varies linearly with CO2 mole fraction. For a given mole fraction and temperature, mixtures become more exothermic as pressure decreases. These trends were analyzed in terms of molecular interactions, phase equilibria, density and critical parameters previously reported for (CO2+EA). Excess molar enthalpies here reported were correlated using the Soave–Redlich–Kwong and Peng–Robinson equations of state, and the classical mixing rule with two binary interaction parameters. The influence of the thermal effects on the phase behavior of (CO2+EA) mixtures formed in supercritical antisolvent precipitation experiments was discussed.