Vapour–liquid-equilibria and calculations using the Redlich–Kwong-Aspen-equation of state for tristearin, tripalmitin, and triolein in CO2 and propane

The data base of experimentally determined phase-equilibria of high boiling molecules with gases is very small compared to the need for these data. With the knowledge of binary phase equilibria, it will be possible to predict the performance of the separation of fat mixtures by gas extraction or crystallisation. Vapour–liquid equilibrium measurements have been carried out with tristearin, tripalmitin, and triolein in mixtures with CO2 or propane. It is known that carbon dioxide has a negligible solvating power for many high boiling molecules. Propane can be an interesting alternative for, e.g., gas extraction. Compositions of the equilibrated phases have been determined experimentally at a pressure up to 52 MPa in a variable volume view cell. Samples from the coexisting phases were taken in order to obtain p–x–y data. The temperatures investigated were 333 and 353 K. Results have been correlated with the Redlich–Kwong-Aspen (RK-Aspen) equation of state. It was possible to obtain a set of interaction parameters for the equation of state and the Mathias–Klotz–Prausnitz mixing rule for the systems with CO2: the relative deviation of calculated and experimental solubility in the gas-phase is high, whereas the absolute deviation is considerably small. For the system with propane, a reasonable fit was obtained. The transition from a gas–liquid to a liquid–liquid miscibility gap in the system containing propane is predicted. Solubility of the triglyceride in propane is much higher than in carbon dioxide.