Liquid-Liquid-Supercritical Fluid Equilibria for Systems Containing Carbon Dioxide, Propane, and Triglycerides

The use of mixed near-critical solvents such as CO2 + propane, for vegetable oil extraction processes, has the advantage of the good solvent capacity of propane together with a nonflammable vapor phase due to the CO2 content. The modeling of phase equilibria of these near-critical solvents with triglycerides using the GC-EOS model has been studied in several works; however, this model is not able to predict correctly the liquid-liquid-vapor region for mixtures of carbon dioxide and propane with triglycerides using the available group binary interaction parameters. In this work, new experimental phase equilibria data on the binary and tertiary systems including CO2, propane, and triacetin are presented. These data are useful to properly assess the interaction parameters of CO2 and propane with the triester group (TG) of the oil molecule. Liquid CO2 is completely miscible with triacetin, and the addition of propane increases the liquid immiscibility of this ternary mixture. This is the opposite behavior presented by mixtures with long-chain triglycerides. in which addition of CO2 increases liquid immiscibility.