Page 229 - Advances in Eco-Fuels for a Sustainable Environment

Advances in bio-oil extraction from nonedible oil seeds and algal biomass 193

solvent extraction can be potentially reduced by using the aqueous enzymatic oil
extraction technique. This process of extraction of oil is observed to be more time
consuming, which is its main disadvantage [37].

7.4.5 Supercritical fluid extraction

The extraction of oil from seeds using various solvent extraction technique has been
found to be more time consuming and problem in solvent disposal. Therefore, the prob-
lem of solvent use as well as time consumption, often in large quantities and toxicity,
SFE technique has been developed. The method has been in practice since the 1980s to
avoid the use of organic solvents as well as to increase the speed of extraction [38]. SFE
using CO 2 has been found to have advantages over solvent extraction [39, 40].
However, the main constraint of the SFE is its high cost at the production scale. This
isnotonlyduetotheusage ofhighpressureequipmentbutalsobecauseoftherawmate-
rial used, which should be freeze-dried to reduce its moisture.

7.4.6 Microwave-assisted extraction

MAE is also called microwave extraction. It is a new extraction technique that is a
combination of microwave and traditional solvent extraction [33]. The MAE process
has many advantages over other extraction processes, such as low cost of production
with shorter time period of processing, less solvent requirement, and a higher extrac-
tion rate with reduced energy consumption and CO 2 emission [33, 41]. The apparatus
and experimental design for the MAE are simple and cheap and also can be used for a
variety of materials with fewer limits on the polarity of extractants [33, 42]. Extraction
of oil using MAE takes less time compared to SFE [43]. Hence, this method of extrac-
tion is found to be a promising alternative to the conventional method of oil extraction,
especially in the case of plant materials [33].

7.5 Purification and processing of nonedible oil

It is well known that viscosity is the main barrier that prevents the use of direct non-
edible oils in conventional diesel engines ([4, 44]). Therefore, in order to bring it in to
usable form, many processing techniques are adapted to produce biodiesel from var-
ious nonedible feedstocks. These methods include pyrolysis, microemulsification,
dilution, and transesterification.

7.5.1 Pyrolysis (thermal cracking)
Pyrolysis is the process of thermal conversion of organic matter using a catalyst in the
absence of oxygen. Thermal decomposition of triglycerides produces alkanes,
alkenes, alkadines, aromatics, and carboxylic acids. The liquid fractions of the ther-
mally decomposed vegetable oils are likely to be used as diesel fuels. The pyrolyzate
is observed to have a lower viscosity and flash point than diesel fuel [30]. Based on the