Green Diesel From Microalgae

This work developed a process of extraction of crude oil from microalgae for production of hydrocarbon based fuel (green diesel). The microalgae Tetradesmus obliquus were cultivated in 12 m3 compact photobioreactors (FBRS) for 15 days using biodigester effluent as nutrients. Microalgae oil was obtained from the dry biomass through hot extraction with organic solvents (hexane and ethanol). After extraction the solvents were recovered from the sample using evaporation methods. After solvent recovery, the results showed that with pure ethanol, only 1.7% w/w crude oil was obtained, whereas with a mixture of hexane and ethanol the yield was 11.1% w/w. Fractional distillation was used as purification methods of the compounds in order to separate the nonsterifiable portion. The first process (pure hexane) after purification delivered 0.4% w/w, and the second process (hexane and ethanol) yielded 6.3% w/w. In addition, the sample was characterized using gas chromatography coupled to a mass spectrometer (GC-MS). An average of 70.6% w/w hydrocarbons ranging from C11 to C22 was found in the first experimental condition, and the main compounds were undecane (8.1% w/w) and pentadecane (10.62% w/w). For the second experimental condition, about 79.6% w/w hydrocarbons were found that varied from C13 to C23 and the main compounds were pentadecane (13.5% w/w) and heptadecane (11.28% w/w). The lower heating value of the purified microalgae oil was measured as 42,464.6 kJ·kg−1, whereas petroleum-based diesel has a lower heating value of 42,500.2 kJ·kg−1. In sum, green diesel from microalgae was proven to have potential to be a concrete alternative to replace diesel from the technical point of view.