Thermodynamics of cholesterol compounds in supercritical carbon dioxide: Experimental and modeling studies

Abstract

The equilibrium solubilities of cholesterols and its acetate, butyrate and benzoate in supercritical carbon dioxide were measured using a continuous-flow method over a wide range of pressure and temperature. Significant difference in the solubility of these compounds is observed and is due to their different vapor pressure and polarity. The solubility is significantly enhanced by adding a polar cosolvent into supercritical carbon dioxide. Also examined was the solubility behavior of physically-mixed cholesteryl butyrate and cholesteryl benzoate in pure supercritical carbon dioxide. The observed solubility decrease is strongly dependent on the bed composition. Besides, formation of ultrafine particles of aspirin and poly-lactic-co-glycolic acid through rapid expansion of supercritical solutions was investigated. The solubility data were successfully modeled using the equation of state approach and density-based correlations. Furthermore, a molecular-based Perturbed Lennard-Jones Chain equation of state and a modified Peng-Robinson equation of state were employed to describe the supercritical phase behavior.