Extraction of lipids from microalgae using CO2-expanded methanol and liquid CO2

•Solvents were tested for extraction of lipids from Botryococcus braunii.•Liquid CO2 only requires 6.8 MPa and is very selective for nonpolar lipids.•CO2-expanded methanol extracts more lipid per mL of organic solvent than methanol.

The use of CO2-expanded methanol (cxMeOH) and liquid carbon dioxide (lCO2) is proposed to extract lipids from Botryococcus braunii. When compressed CO2 dissolves in methanol, the solvent expands in volume, decreases in polarity and so increases in its selectivity for biodiesel desirable lipids. Solid phase extraction of the algal extract showed that the cxMeOH extracted 21 mg of biodiesel desirable lipids per mL of organic solvent compared to 3 mg/mL using either neat methanol or chloroform/methanol mixture. The non-polar lCO2 showed a high affinity for non-polar lipids. Using lCO2, it is possible to extract up to 10% neutral lipids relative to the mass of dry algae. Unlike extractions using conventional solvents, these new methods require little to no volatile, flammable, or chlorinated organic solvents.