The process parameters and solid conditions that affect the supercritical CO2 extraction of the lipids produced by microalgae

• Mass transfer controlled the rate of supercritical extraction of oil from microalgae.
• Mechanical or thermal cell wall rupture improved internal mass transfer.
• The extraction rate on microalgae with moisture content over 30% was reduced.
• While external mass transfer increased with flow rate, a minimum contact time was required.
• Oil extraction yield was 21% at 300 bar, 70 °C, and 72 kg CO2 h−1 kg biomass−1.

This paper describes the impact that process parameters and solid conditions have on the supercritical extraction of oil from Chlorella protothecoides that are grown in heterotrophic conditions. Pressure was tested from 150 to 300 bar and temperature from 35 to 70 °C. In the harshest conditions, the extraction curve slope was close to the theoretical oil solubility. Mass transfer controlled the global rate. Mechanical or thermal cell wall rupture improved the extraction rate; however, it was dependent on the microalgae humidity. The extraction rate on samples that had over a mass fraction of 30% moisture content was greatly reduced. Cell disruption methods, such as sonication or microwaving, were not useful on the wet biomass because the water created a barrier. External mass transfer improved with flow rate (from 1 to 5 g min−1) but a minimum contact time was required. The optimum was 3 g min−1 (72 kg CO2 h−1 kg biomass−1). A maximum oil fraction of 210 g kg−1 biomass (wo = 21%) was achieved.

Supercritical carbon dioxide extraction curves of the oil contained in Chlorella protothecoides microalgae at different: (a) operation conditions and (b) microalgae humidity.Figure optionsDownload as PowerPoint slide