Sequential Extraction and Purification of Triglycerides and Carotenoids with Supercritical Carbon Dioxide for Valorization of the Integrated Algal Biorefinery

The costs associated with producing renewable biofuels from algae have been prohibitive to their commercialization. However, an integrated biorefinery approach, in which additional high-value and high-purity products are coproduced from algae, can favorably shift the economics of the system. Of importance to realizing renewable fuels and chemicals sustainably, this work aligns with principles of green chemistry and green engineering by using nontoxic, green solvents through supercritical fluid extraction (SFE) methods. Here, a supercritical CO₂ (scCO₂) flow-through extraction system is used to target recovery of triglycerides (including biodiesel precursors and eicosapentaenoic acid, an omega-3 fatty acid) and carotenoids (“super-antioxidants”, such as fucoxanthin) from the microalgae, Phaeodactylum tricornutum, to yield high-value enriched extracts as nutraceutical products. Sequential extraction schemes that leverage the tunable polarity of SFE through modulating the pressure of scCO₂ and volumes of ethanol as a cosolvent are deployed with steps that extract triglycerides selectively, fucoxanthin selectively over chlorophyll, or a high yield of carotenoids (i.e., fucoxanthin and chlorophyll), albeit unselectively. An economic analysis modeling a full-scale SFE plant of these schemes indicates that in certain scenarios, profitability can be achieved from the sale of eicosapentaenoic acid and fucoxanthin products alone, enabling lower-value product recovery for fuller biomass utilization.