Page 238 - Advances in Eco-Fuels for a Sustainable Environment

202 Advances in Eco-Fuels for a Sustainable Environment

of this technology is achieving a homogenous phase after the evaporation of the vapor
phase and the separation of liquid beyond the critical point. The supercritical phase
helps in the transformation of the fluid into a supersolvent, which simultaneously
increases the efficiency of extraction [92].
There are some new supercritical fluids that are currently being explored for the
extraction of lipid: ethylene, CO 2 , ethane, methanol, ethanol, benzene, toluene, and
water [93]. According to Halim et al. [27], the wet mass of Chlorococcum sp. was
extracted using supercritical CO 2 and the lipid yield was found to be around 7.1%
at the critical temperature of 60°C, the critical pressure of 30Mpa, and an extraction
time of 80min. The lipid yield was found to be higher when obtained from wet bio-
mass than from dry biomass (5.8%), which also significantly reduces the cost and
energy involved during the drying of biomass. Soxhlet extraction was found to be less
efficient (5.8%) when compared to supercritical extraction. The lipid yield attained
from the Bligh and Dyer method was found to be nearly double that of supercritical
CO 2 . Therefore, this indicates that the microalgae strains and culture conditions play a
significant role in determining the appropriate lipid extraction methods. Hence, the
design of an extraction technique should be done wisely to reduce the total energy
involved during the extraction process.

7.8.3 Bligh and dyer method
This method is considered to be more efficient for both wet and dry biomass. The
highest lipid extraction of 95% was obtained through this method. The ratios of
methanol, chloroform, and water should be 2:1:1.8 and the mixture was mixed
throughly to form a homogeneous monophasic phase. Considering the critical ratios
of solvent for the dry route, its water content is insignificant in comparison to the
biomass; while for the wet route because of high water content, methanol, chloro-
form and water ratioof2:2:1.8 should be takenintoaccount forextractionprocess
[94]. The homogenization of cells by centrifuge separates the biphasis layer (lipid
dissolved in chloroform and methanol dissolved in water) formed in the process.
Thereafter, the lipid fraction is separated from chloroform and the methanol from
water by fractional distillation [94].

7.8.4 Ionic liquids

Ionic liquids are known as green solvents that possess low toxicity and relatively no
vapor pressure. The ionic liquids contain large asymmetric organic cations coupled
with organic and inorganic anions. The mixture of ionic liquids with methanol
(CF 3 SO 3 and MeSO 4 ) was used for the extraction of lipid from the algal biomass.
The extraction of lipids highly depends on the anion structure. Ionic liquids combined
with the Bligh and Dyer method were found to be efficient for the extraction of the
lipid (12.5% and 11.9%, respectively) whereas only 10.6% of the lipid was extracted
by the Bligh and Dyer method [95, 96].