Measurements and modeling of the solubility of ergosterol in supercritical carbon dioxide

In this work, the solubility of ergosterol, which is a natural phytosterol exhibiting cholesterol-lowering properties and is of particular interest to the food and nutraceutical industries, in supercritical carbon dioxide was measured with a semi-flow type phase equilibrium apparatus. The solubility experiment was performed at pressures in the range of 120–240 bar and at temperatures of 318.15, 323.15, and 333.15 K, and the measured solubility ranged from 2.9 × 10−6 to 3.0 × 10−5. The high-pressure solubility data for each isotherm were correlated by the Schmitt–Reid and Giddings models with average absolute relative deviations (AARD) ranging from 4.1 to 9.7% and 2.2 to 5.5%, respectively. The Chrastil model and the Méndez-Santiago and Teja model were also used to fit the entire data set yielding AARDs of 7.6% and 8.5%, respectively. Furthermore, the Peng–Robinson equation of state (EOS) using one-parameter and two-parameter van der Waals mixing rules was employed to fit the experimental solubility data with the latter giving a significantly smaller AARD of 6.4%. Retrograde behavior of the solute's solubility in the supercritical fluid was observed and was also predicted by the equation of state.

► Solubility data of ergosterol, a cholesterol-lowering phytosterol, were reported.
► Four correlation models were employed to fit the high-pressure solubility data.
► Solubility data were well correlated by the PR-EOS with the vdW-2 mixing rules.
► Merits and limitations on the use of the EOS and correlation models were compared.
► Retrograde behavior was observed and was also rigorously predicted by the PR-EOS.