Laboratory extraction of microalgal lipids using sugarcane bagasse derived green solvents

Three green solvents were tested for lipid extraction based on the Bligh and Dyer method. Lipids from the microalgae Chlorella pyrenoidosa were extracted through the tertiary systems 2-methyltetrahydrofuran:isoamylalcohol:water (1:3, 1:2, 1:1, 2:1, 3:1 v/v) and 2-methyltetrahydrofuran:ethanol:water (3:1 v/v). For comparative effect, extractions with chloroform:methanol:water (3:1, 2:1, 1:1, 1:2, 1:3 v/v), with binary systems 2-methyltetrahydrofuran:water, isoamyl alcohol:water, chloroform:water, n-hexane:water, and monophasic systems 2-methyltetrahydrofuran (2-MeTHF), isoamyl alcohol, chloroform and n-hexane were used. The Bligh and Dyer method using green solvents was highly efficient, although some undesirable components were extracted, especially when larger volumes of isoamyl alcohol were used. System 2-MeTHF:ethanol:water formed only a biphasic system when it was used in a 3:1 (v/v) proportion, obtaining 64% of fatty acids. The chloroform:methanol (1:2 v/v) system extracted 122.2 ± 1.9 mg g−1, in which 92.4% consisted of fatty acids. In systems using green solvents, the extractions with the system 2-MeTHF:isoamyl alcohol (2:1 v/v) achieved a 78% selectivity (99.6 ± 7.6 mg g−1of fatty acids) and an 88.2% efficiency when compared with the reference system chloroform:methanol 1:2 (v/v).The fatty acids profile showed that extractions with 2-MeTHF:isoamyl alcohol had higher percentages of fatty acids with low degree of unsaturation, which is ideal for the production of better quality biodiesel. The results obtained suggest that2-MeTHF:isoamyl alcohol (2:1 v/v) can replace the chloroform:methanol system currently used. At an industrial level, this system still requires some technical improvements related to the energy expenditure for solvent evaporation, and at an economic level, the high price of the 2-MeTHF makes the process impracticable compared with hexane.