Understanding the wettability of different surfaces for the fractionation of complex lipid mixtures using supercritical carbon dioxide
Creators: Santos Hernandez, Eileen Vanessa
Publisher: name: University of Alberta Library
Year: 2024

<p>Supercritical fluid fractionation of complex lipid mixtures has emerged as a green alternative for conventional methods. Packed columns have been used to fractionate diverse lipid mixtures using supercritical carbon dioxide (SC-CO2) under different conditions. However, there is a lack of fundamental knowledge about how the contact between the phases at the packing level is affecting process performance. Therefore, a systematic approach was taken to determine the wettability of different lipid classes on diverse surfaces in SC-CO2 and to correlate it with the fractionation process outcomes of a model mixture.<br>
The first study aimed to determine the effect of pressure and temperature on the interfacial tension (IFT) and equilibrium contact angle (CAeq) of corn oil in air, SC-CO2 and SC-N2 on polished stainless steel (SS) metal sheet under unsaturated and saturated surrounding phases at 40, 60, 80 °C and 0.1, 16, 20, 24 MPa. The IFT of corn oil/N2 and corn oil/CO2 showed a remarkable difference depending on pressure and temperature conditions where the IFT of corn oil/CO2 decreased dramatically with pressure. The wetting behaviour of corn oil on polished SS surface under dense N2 and CO2 was characterized as complete wetting, showing CAeq values below 10°, mainly influenced by the saturation or unsaturation condition of the environment.<br>
The objective of the second study was to determine the IFT and the CAeq of oleic acid (OA) and canola oil (CanO) on polished glass in SC-N2 and SC-CO2 environments at 40, 60, 80 °C and 16, 20, 24 MPa. The IFT of OA and CanO in SC-CO2 at 60 ºC and pressures of up to 24 MPa showed a remarkable decrease with pressure. CAeq of the OA/SC-CO2 system on glass exhibited partial to complete wettability at 40 ºC and 60 ºC, while complete wettability was obtained at 80 ºC from 16 to 24 MPa. In contrast, CanO/SC-CO2 exhibited three different wetting patterns on glass surface with complete wettability at 40 ºC, partial wettability at 60 ºC and partial to complete wettability at 80 ºC with an increase in pressure. Some novel surface phenomena of lipids on solid surfaces in SC-CO2 medium were identified in both studies, including bouncing of lipid droplets on polished SS and glass surfaces, sliding of the CanO droplet on glass surface, supercritical fluid cavity formation during droplet spreading and satellite droplet formation.<br>
The main goal of the third study was to determine the effect of process parameters (temperature, pressure, solvent-to-feed (S/F) ratio and different types of packing) on the output variables of extract yield, free fatty acid separation efficiency (FFA-SE) and dynamic hold-up (DH) amount. Continuous countercurrent fractionation of a model mixture (85% FFA and 15% triacylglycerol (TAG)) was performed using three different types of packing (stainless steel perforated and beads, and glass beads) at S/F ratios of 15 and 25, pressures of 16 and 24 MPa and temperatures of 40 °C, 60 °C and thermal gradient of 60-100 °C. The extract yield and FFA-SE at isobaric conditions were significantly affected by temperature. At isothermal conditions, the extract yield and FFA-SE were affected by S/F ratio and pressure, whereas the type of packing had an effect only on FFA-SE. At high S/F ratio, the extract yield was higher since there was a larger amount of CO2 to solubilize lipids, specifically lighter molecular weight FFA, resulting in higher extract yield and higher FFA-SE. CO2 density increased with pressure, resulting in higher extract yield as well as FFA-SE. DH amounts at isobaric conditions were influenced not only by temperature, but also by the type of packing. Differences in packing characteristics affected the DH amounts where lower void volume percentage corresponded to lower contact surface area, leading to higher DH amounts. More wettable packing surface by the lipids resulted in lower DH amount. In addition, CO2 might have a lubricant effect on the holes of perforated packing, inducing disruption of the lipid film, possibly generating an easier mechanism for lipid film renewal, and thus enhancing mass transfer.<br>
The findings of this Ph.D. thesis contribute to better understanding of the relationship between packing wettability and process performance in supercritical column fractionation of complex lipid mixtures and thus can lead to improved equipment design and enhanced process efficiency.</p>