Wet lipid extraction from the microalga Nannochloropsis sp.: Disruption, physiological effects and solvent screening

For biodiesel applications, microalgae and especially Nannochloropsis sp. are considered as a promising feedstock for lipid production. Main issues are high lipid productivity, but also robust and energy efficient downstream processes. In the biorefinery process, cellular mechanical pretreatment and solvent extraction are investigated nowadays to allow wet route lipid recovery. In this study, a method to screen solvents according their performance to extract lipids in wet condition was proposed. It consisted in short liquid/liquid extraction on cells suspension of microalgae partially disrupted. In one test, it allowed identifying for each solvent: (i)the ability to solubilize lipids compounds; (ii)the limitation by the cell wall/membrane and (iii)kinetics. The cell disruption appeared to be the main controlling step if low water soluble solvents were used. Extraction of lipids from suspension of disrupted microalgae was more efficient than extraction from dried biomass (same solvent, same energy and time)and the water presence enhanced the selectivity for saturated fatty acids recovery. 50percent extraction yield was achieved with 84percent disruption rate in 10 min and saturated fatty acids (SFA)content was enriched to 72percent of the extracted lipids. The 11 solvents screening showed a significant impact of the solvent choice on a 10 min batch extraction yield. Based on the criteria considered in this study, the best solvents were Methyl tert-butyl ether (MTBE)and cyclopentylmethyl ether (CPME). They were those with Hansen solubility parameters close to the target fatty acids, low solubility in water and low heat of vaporization. They represent alternatives to chlorinated solvents or alkanes.