Supercritical carbon dioxide extraction of microalgae lipid: Process optimization and laboratory scale-up

• Microalgae lipids were extracted using SC-CO2 and compared to conventional methods.
• Lyophilization effect on biomass surface properties and SC-CO2 extraction were investigated.
• Effects the operating conditions of SC-CO2 extraction were studied.
• Experimental results were used to fit a suitable model and optimize process conditions.
• The process was successfully scaled-up.

Supercritical carbon dioxide (SC-CO2) extraction of lipid from Scenedesmus sp. for biodiesel production was investigated and compared to conventional extraction methods. The effect of biomass pre-treatment prior to extraction and extracting conditions, namely pressure in the range of 200–500 bar, temperatures in the range of 35–65 °C and CO2 flow rate in the range of 1.38–4.02 g min−1, on SC-CO2 extraction yield and quality of lipid were investigated. Three levels full factorial design of experiments and response surface methodology was used to model the system. A second order polynomial model was developed and used to predict the optimum conditions. Scaling up to a laboratory larger scale was also tested. The results indicated that SC-CO2 extraction was superior to other extraction techniques, but exhibited significant variations in yield with changes in operating parameters. In the developed model, it was found that the linear and quadratic terms of the temperature, as well as the interaction with pressure had a significant effect on lipid yield; whereas, their effect on lipid quality was insignificant. The best operating conditions, in the tested range, were 53 °C, 500 bar and 1.9 g min−1, in which lipid extraction yield of 7.41% (dry weight basis) was obtained. Negligible differences were observed when the fatty acid composition of SC-CO2 extracted lipid was compared to that extracted by the conventional methods. At the optimum conditions, SC-CO2 extraction was successfully scaled-up by eight-folds and the extracted lipid yield dropped by 16%.

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