Viscosity measurement and modeling of canola oil and its blend with canola stearin in equilibrium with high pressure carbon dioxide

During enzymatic reactions carried out in supercritical CO2 (SCCO2) media, CO2 can expand the liquid reactant mixture, especially lipid-type substances, due to pressure increase and dissolution of CO2, causing viscosity reduction, and improvement of the diffusion of reactants and products. For better understanding of the transesterification reaction of canola oil and canola stearin in SCCO2 media, the viscosity of canola oil at 40, 50, 65, and 75 °C and its blend with canola stearin (30 wt%) at 65 °C in equilibrium with high pressure CO2 was measured up to 12.4 MPa using a rotational rheometer equipped with a high pressure cell. The solubility of CO2 in canola oil at 40 and 65 °C and its blend with canola stearin at 65 °C was also determined at pressures of up to 20 MPa using a high pressure view cell. The viscosity of canola oil at 40, 50, 65, and 75 °C and its blend with canola stearin at 65 °C decreased exponentially to 87.2, 84.7, 74.8, 66.2, and 74.2% of its value at atmospheric pressure, respectively, with pressure increase up to 12.4 MPa. The viscosity of the samples decreased with an increase in temperature, but the effect of temperature diminished above 10 MPa. The viscosities of CO2-expanded canola oil and its blend with canola stearin at 65 °C were similar up to 12.4 MPa. The samples exhibited shear-thickening behavior as the flow behavior index reached almost 1.2 at elevated pressures. The mass fraction of CO2 in canola oil at 40 and 65 °C and its blend with canola stearin at 65 °C reached 24 and 21% at 20 MPa, respectively. The Grunberg and Nissan model was used to correlate the viscosity of CO2-expanded lipid samples.