Prediction of the best cosolvents to solubilise fatty acids in supercritical CO2 using the Hansen solubility theory

Abstract

Cosolvents are employed to improve the extraction efficiency and modify the selectivity of the main solvent. However, choosing a proper cosolvent in supercritical extraction is an arduous task. This study aimed to predict the best cosolvents for the supercritical CO2 extraction of oleic and linoleic acids using the Hansen solubility theory. Calculations were performed for eight organic cosolvents used in food and pharmaceutical production. The best cosolvents for the solubilization of both fatty acids were short-chain alcohols, ethanol and methanol. The predictions were validated with bubble pressures of the mixtures with a 0.003 fatty acid molar fraction at temperatures of 313.2 K and 323.2 K. The experimental results agreed with the predictions. The effect of pressure was well predicted via the direct relationship between pressure and the solvent density. However, the impact of temperature was not properly foreseen because the variation of solute vapour pressure was not considered. The Hansen theory predicted that the miscibility enhancement of the solute in the supercritical mixture is maximum at low pressures and low cosolvent concentrations, as was experimentally confirmed.