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.