Viscosity measurement and modeling of lipid supercritical carbon dioxide mixtures

The viscosities of supercritical carbon dioxide (SC-CO2) containing different levels of methyl oleate and oleic acid were measured with a high pressure capillary viscometer. The SC-CO2-methyl oleate system was evaluated at 313.15, 323.15 and 333.15 K and 11.5, 13.7 and 15.5 MPa, respectively. The SC-CO2-oleic acid system was evaluated at 313.15 K and 20.5 and 30.0 MPa and 333.15 K and 30.0 MPa. The increase in SC-CO2 viscosity was as high as 15-20% at the maximum methyl oleate concentrations (4-5 wt%) and 6-12% at the maximum oleic acid concentrations (2-3 wt%). The increase of relative viscosity with concentration was linear. The lipid-SC-CO2 mixtures were Newtonian. The Arrhenius equation, modified by the excess Gibbs free energy using solubility parameters of the components based on the regular solution theory, predicted the liquid phase and the fluid phase viscosities of the lipid-SC-CO2 mixtures within +/-25% and +/-1%, respectively. (C) 1998 Elsevier Science B.V