Vapor-liquid and vapor-liquid-liquid equilibrium compositions have been measured for the ternary systems CO2 + H2O + acetic acid at 313 and 333 K, CO2 + H2O + propionic acid at 313 K, and CO2 + H2O + n-butyric acid at 313 K, at pressures between 2.0 and 20.0 MPa. For all systems, a three-phase equilibrium region was observed at pressures comparable to the critical pressure of pure carbon dioxide. The extent of the three-phase equilibrium region increases with the hydrocarbon chain length of the acid, while the pressure for the appearance of three phases also increases with temperature. The distribution coefficient of the acids between the supercritical fluid phase and the aqueous phase at pressures above the critical pressure of pure carbon dioxide increases with the hydrocarbon chain length of the acid: higher molecular weight acids were found to be preferentially partitioned into the supercritical fluid phase. The experimental data for the ternary systems were correlated by using a cubic equation of state and a recently proposed density-dependent mixing rule with model parameters derived from binary data only.
ASJC Scopus subject areas
- Chemical Engineering(all)