Page 228 - Advances in Eco-Fuels for a Sustainable Environment

192 Advances in Eco-Fuels for a Sustainable Environment

process to around 89% in single pass and 91% in a dual pass [32] (Achten, 2008).
Oil extracted from a mechanical press needs further treatment by filtering and
degumming [30].

7.4.2 Chemical or solvent extraction

Solvent extraction is the process of removal of a solute component from the solid by
using a liquid solvent; it is called leaching or solid-liquid extraction. According to
this method, n-hexane yields the higher amount of oil compared to other solvents
[28]. There are various factors such as particle size, solvent type, and temperature
that were found to affect the extraction of oil [30]. The small particle size is preferred
as it allows for a large interfacial area between the solid and liquid. The solubility of
the material increases with an increase in temperature. Agitation of the solvent
increases the eddy diffusion and therefore increases the transfer of materals from
the surface to the particles [4, 33]. It is observed that low viscosity solvents are pre-
ferred to circulate freely during extraction. The chemical oil extraction technique
was found to be very effective because of high oil yield and consistent performance.
In addition, this method has a negative environmental impact because of the waste-
water generation, higher specific energy consumption, and higher emission of
volatile organic compounds as well as fewer human health impacts [30].There
are three methods of extraction of this type:
i. Hot water extraction.
ii. Soxhlet extraction.
iii. Ultrasonication technique.

7.4.3 Accelerated solvent extraction
ASE is also called pressurized solvent extraction (PSE), this is one of the modern
extraction processes. According to this method, the oil from seeds is extracted by
using organic or aqueous solvents at elevated temperatures and pressures. It was
observed that elevated pressure prevents boiling at temperatures above the normal
boiling point of solvent but high temperature accelerates the extraction rate of oil. This
method has reduced time as well as solvent consumption when compared to the other
solvent extraction techniques [40]. ASE has been used for the extraction of different
materials, including wheat germ [34] and flaxseed hulls.

7.4.4 Enzymatic extraction

The aqueous enzymatic oil extraction (AEOE) method is an endowed technique for
the extraction of oil from plant materials [35]. The main advantages of this processis
are its environmentally friendly nature and the fact that it does not produce any harm-
ful or volatile organic compounds [36]. Suitable enzymes are used to extract the oil
from pretreated seeds. A combination of enzymatic extraction with ultrasonication has
shown better results in oil extraction from seeds. Yet the problems associated with