Page 239 - Advances in Eco-Fuels for a Sustainable Environment

Advances in bio-oil extraction from nonedible oil seeds and algal biomass 203

7.9 Enzymatic oil extraction

Enzymatic oil extraction is one of the promising techniques for the extraction of oil. In
this process, suitable enzymes are used for the extraction of oil from seeds. This type
of extraction is also known as a green process as it does not produce any volatile com-
pounds during the extraction process; this process was declared to be a hazard-free
extraction technique. The only disadvantage associated with this process is the dura-
tion involved during the extraction [96a]. A combination of ultrasonication and aque-
ous enzymatic methods was used for the extraction of oil from Jatropha curcus seed
kernels. The use of n-hexane as a solvent during extraction generated a large amount
of wastewater along with the emission of volatile compounds. The use of enzymes
greatly reduces the core problems faced during solvent extraction. The use of alkaline
protease along with ultrasonication pretreatment reduced the cost and energy involved
during the conventional extraction process [97].In Chlorella sp., 56% of the lipid was
extracted by enzymatic hydrolysis with immobilized cellulose. The lipid extraction
was increased by 1.73-fold by enzymatic hydrolysis with cellulose on C. vulgaris cul-
tures. Enzymes such as lysozyme, snailase, trypsin, and alkaline protease were
reported with a lipid content of 16.6%, 35%, 12%, and 8%, respectively [98–100].

7.10 Conclusions

The biofuel produced from nonedible oil seeds can play a vital role in meeting the
energy demands of the growing worldwide population. This is mainly important as
the second-generation biofuel is produced from nonedible sourced and from waste-
lands that require less maintenance, less soil fertility, and less water. The solvent
extraction technique using n-hexane in nonedible seeds was observed to have the
highest oil yield, which makes it the most common type of extraction among the three
techniques. Though the solvent extraction is found to be a very effective method for
oil extraction, its cost of production is moderately higher due to the higher cost of the
solvent. This chapter has covered various technologies for the separation of lipids
from microalgal biomass. However, an ideal method has not yet been identified. There
are three major problems associated with lipid extraction: (1) No efficient cell disrup-
tion method has been developed for wet biomass. To disrupt the rigid cell envelope of
microalgae, a synergistic approach that combines different techniques might be pref-
erable to using a single method. (2) There is no reasonable way to compare the dif-
ferent methods that have been developed. The energy consumption or material cost
should be considered when comparing the different methods, but each investigation
was performed under very different conditions, which makes it difficult to compare
them to each other. For example, the water content of wet biomass critically affects
the extraction or cell disruption efficiency. Thus, the process variables, such as the
water content, should be standardized for biodiesel production, which would help inte-
grate the research results obtained from various investigations. (3) The postextraction
processes were not considered. Various lipid extraction techniques affect the conver-
sion (transesterification) or purification processes differently. Thus, the economic