POLAR AND NONPOLAR COSOLVENT EFFECTS ON THE SOLUBILITY OF CHOLESTEROLIN SUPERCRITICAL FLUIDS

The solubility of cholesterol in supercritical carbon dioxide and etha ne containing small amounts (1.76-6.0 mol %) of acetone and hexane cos olvents has been measured. The data show an unusual reversal of cosolv ent effects in the different primary supercritical fluids. These resul ts are interpreted in terms of the competition between dispersion and dipole interactions and the molecular features of cholesterol. The hig hest solubility is observed in the ethane-acetone system where ethane interacts with the hydrocarbon backbone of cholesterol and acetone int eracts with the polar OH group. The results are correlated with a modi fied form of the Peng-Robinson equation of state. The necessity of cha racterizing solute properties for supercritical fluid extraction of bi omolecules is highlighted.