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Simultaneous Extraction, Fractionation, and Enrichment of Microalgal Triacylglyerides by Exploiting the Tunability of Neat Supercritical Carbon Dioxide

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journal contribution
posted on 12.10.2016, 00:00 by Thomas A. Kwan, Qingshi Tu, Julie B. Zimmerman
Continuous flow supercritical carbon dioxide (scCO2) was used to simultaneously extract, fractionate, and enrich simultaneously triacylglycerides (TAGs) of different carbon chain lengths and degrees of unsaturation from a 6-component mixture of analytical standards and from Chlorella sp., a common microalgae used as biodiesel feedstock. Evidence is presented that solubility for a given TAG can be enhanced or diminished in the presence of other, dissimilar TAGs due to solute to solute interactions and scCO2 densities. Comparison of analytical standard and Chlorella sp. extracts suggests that TAG mixtures and biomass matrices influence extraction behavior with the same TAG behaving differently depending on the starting material. This was validated by fitting Chrastil’s solubility parameters to indicate which TAGs were most susceptible to solute to solute interactions and neat CO2 density. A model was developed comparing the energy requirements for the downstream purification of TAGs trimyristin (C14:0), tripalmitin (C16:0), and trierucin (C22:1) from mixtures extracted with the scCO2 method developed here. The model outputs suggest trade-offs for over- or under-enriching certain TAGs using neat scCO2. Both the experimental and modeling results demonstrate the potential of scCO2 to be used as an initial fractionation and enrichment tool whereby the associated energy and economic costs of downstream processing, such as distillation, can be reduced.