Ternary solubility of mixed cholesteryl esters in supercritical carbon dioxide

The solubilities of equal-mass mixed cholesteryl benzoate (CBE) and cholesteryl butyrate (CBU) in supercritical carbon dioxide were determined at 308.15, 318.15 and 328.15 K, and over pressure ranging from 12.0 to 24.0 MPa. The solubility of both solutes in the ternary system is observed to decrease relative to the value of the corresponding binary system. As compared with their respective binary system, the CBU ternary solubility decreases greatly by around 65% and the CBE one does by approximately 10%. These uncommon observations may be related to their similar chemical structures. The selectivity of supercritical CO2 to the solid mixture is found to decrease as extraction temperature or pressure increases. Separation of the equal-mass mixed solids could result in over 90% pure CBU. The Peng–Robinson equation of state and four empirical density-based models are used to correlate the ternary solubility data. These models generally perform very well with a global average absolute relative deviation less than 10%. The fugacity calculations show that either CBU or CBE has lower fugacity in the ternary system than in the binary system, possibly responsible for the solubility diminution found in the ternary system.