Enhancing Triglyceride Production Using Carbon Dioxide
Microalgae , Biodiesel , Lipid Extraction , Liquid Carbon Dioxide , Switchable-Hydrophilicity Solvent
Biofuels have recently emerged as renewable, biodegradable, and cost-effective alternatives to fossil fuels. Microalgae serve as promising feedstocks to produce biofuel because of their fast growth rates, ability to grow on non-arable land or in wastewater, and high lipid content, which is essential for biofuel production. Unfortunately, current laboratory methods for the extraction of microalgal lipids have high capital/energy costs. Therefore, this thesis examines liquid CO2 as a potential greener technique for extracting these intracellular lipids. In the literature review, microalgal cell disruption and extraction techniques are discussed extensively. Current extraction techniques, with or without cell disruption, have high energy and capital costs. Therefore, it is essential to discover greener extraction techniques. Other improvements to reduce cost include using microalgal slurries, combining process steps, and minimizing solvent use. Life cycle assessments are necessary to identify the environmental impact associated with each lipid extraction method. The lipid extract yields from Chlorella vulgaris using liquid CO2, co-solvents, and/or additional modifiers, were investigated. When C. vulgaris in the presence of dodecyltrimethylammonium bromide and water was exposed to liquid CO2, the highest extract yield was obtained compared to all other co-solvents and/or modifiers tested. In a study of the transesterification of soybean oil using a switchable-hydrophilicity solvent, 2-(dibutylamino)ethanol, fatty acid methyl ester yields and the recyclability of 2-(dibutylamino)ethanol were reported. After 5 cycles, the yield of fatty acid methyl esters was 80-85 % of the original mass of soybean oil and the recovery of 2-DBAE was 65-90 % of the original volume. This project served as a proof of concept for future applications to microalgae. The extraction of lipids from Scenedesmus sp. using liquid CO2, methanol, and/or prior cell disruption techniques was investigated. When microwave radiation in the presence of distilled water followed by extraction using liquid CO2 and methanol, the highest neutral lipid and free fatty acids yields were obtained. Moreover, fluorescence microscopy was able to effectively monitor cell disruption upon microwave radiation and grinding following freezing with liquid N2.