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Coupled Supercritical CO2 - Membrane Technology for Lipid Separations
- Author / Creator
- Akin, Oguz
Coupling supercritical CO2 extraction with membrane separation leads to energy savings by recycling CO2 at supercritical state while separating extract components. Commercially available polyamide-based membranes are commonly used with coupled systems due to their availability and robust structures. However, high pressure operating conditions may cause physicochemical and morphological changes in polymer membranes, which in turn can adversely affect membrane performance.
Since most of the information on commercial reverse osmosis membranes is proprietary, further investigation on their structure would be beneficial for selection of the proper membranes, especially for processes involving various solvents such as supercritical CO2. Therefore, detailed characterization of four polyamide membranes was performed using advanced instrumental techniques for better understanding of their physicochemical and morphological properties. Findings suggest that AK and AG membranes had excess of intermolecular hydrogen bonds, while SG and SE had modified covalently cross-linked structure.
Temperature, pressure and CO2 flux were the major processing parameters investigated to assess the interactions between the polyamide membranes and CO2. The observed interactions between the polymer and CO2 were attributed to Lewis acid and base interactions and hydrogen bonding. The change in surface hydrophobicity and drop in absorbance of particular functional groups were determined as indicator of physicochemical changes in the structure. Morphological changes were also observed upon processing with supercritical CO2 up to 24 h.
Performance of the membranes was tested using pure oleic acid retention and separation of a triacylglycerol/oleic acid mixture. Covalently cross-linked membrane structures were found to be more resistant to supercritical conditions. Reorganization of the polymer network due to interactions during CO2 exposure affected the membrane performance dramatically.
Investigation of performance and stability of polyamide membranes clarified the major factors responsible for adverse effects on their structures such as swelling and plasticization during processing. Results obtained in this thesis research contribute both to the fundamental understanding of polymer membrane behaviour under supercritical conditions and to the type of membrane materials needed for such novel process development without sacrificing membrane performance.
- Graduation date
- Fall 2011
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.