Prediction of solubility of solid biomolecules in supercritical solvents using group contribution methods and equations of state

Abstract

The purpose of this study is to present a method to estimate the solubility of solid solutes in supercritical fluids when only the molecule structure is known. The solubility of solid solutes in a supercritical fluid is an important thermo-physical property that needs to be determined if one is to develop a generic supercritical fluid extraction model. Due to the general lack of solubility data and/or pure component property data needed to estimate solubility, a need exists to develop methods to estimate the solubility of solid solutes in a supercritical solvents using limited information. Group contribution methods were used to estimate pure component properties, equations of state (Lee-Kesler-Plocker (LKP) and Mohsen-Nia-Moddaress-Mansoori (MMM) were then used to estimate the PVT behaviour of the solvent and the fugacity coefficient of solute in the solute-solvent mixture. The solubilities of β-carotene, cholesterol, nimodipine and nimbin in supercritical solvents were determined. Our results show that the LKP model provides the best fit for β-carotene and nimodipine in SCCO2 and the MMM model is best for cholesterol in SCCO2 and SCC2H6 and for nimbin in SCCO2. The Aromaticity Index (AI) seems to be an important parameter for determining which model will perform best; based on the systems analysed here, one should use the LKP EOS when AI > 0.3, otherwise use the MMM EOS. © 2008 Academic Journals Inc.