Extraction of bio-oils from algae with supercritical carbon dioxide and co-solvents

Supercritical carbon-dioxide (SC-CO2) is a clean and green technology for extracting bio-oil/lipids from algae (Nannochloropsis sauna) for biofuel production and high-value co-products development. A mixed-polarity azeotropic mixture (hexane/ethanol) modifier/co-solvent was added to enhance the SC-CO2 fluid affinity towards neutral lipid and polar lipids. The benefits of inducing mixed polarity solvents include enhanced solvent properties, favorable mass transfer, higher lipid yield, and better lipid quality. A microwave pretreatment prior to supercritical extraction was employed to improve lipid extraction efficiency and reduce extraction energy consumption. The effects of pressure, temperature and co-solvents to algae ratio on lipid extraction yield and fatty acid composition were investigated. A micro-elemental analysis (CHNOS) of total and neutral algal lipid samples was performed according to ASTM methods. The algal biomass characterization and algal lipid analysis were performed using several analytical instruments such as FTIR, SEM-EDS, TGA, Confocal microscopy and GC-MS.