Fluid phase equilibrium studies on ternary and quaternary mixtures of carbon dioxide with 1-dodecanol, dodecanoic acid, quinoxaline and 1,8-octanediol at 393.2 K and at pressures up to 40 MPa

Isothermal and isobaric phase tetrahedra were determined for the quaternary systems CO2 + 1-dodecanol + dodecanoic acid + (quinoxaline or 1,8-octanediol) at 393.2 K and pressures from 10 to 40 MPa. In addition, isothermal measurements were performed on the ternary subsystems CO2 + 1-dodecanol + dodecanoic acid, CO2 + 1-dodecanol + quinoxaline and CO2 + dodecanoic acid + quinoxaline under the same conditions. From the results separation factors for 1-dodecanol and dodecanoic acid were calculated. The data are discussed in relation to the effect of moderators (here quinoxaline or 1,8-octanediol) on the selectivity of supercritical fluid extraction (SFE) using carbon dioxide as a supercritical solvent.