Biomedical Engineering Reference
In-Depth Information
the result presented, high concentration of methanol will inhibit the transesterification
reaction and stepwise addition of methanol can avoid the cell denaturaliation. The methyl
ester contain could reach about 90% within 72 hrs using cross-linked immobilizedcell with
glutaraldehyde treatment as biocatalyst. The lipase activities of the cell could be maintained
after 3 batch cycles. These results indicate that the use of immobilized- cell as biocatalyst
shows a significant meaning and provides an alternative potential tool of biodiesel
manufacture due to the simplicity of lipase preparation and long period stability of the
biocatalyst [32].
3. Selection of Feedstock
The central reagent of the reaction is the actual triglyceride. As stated earlier, this can be
any vegetable oil, animal fat, or waste cooking oil. While vegetable oil, or straight vegetable
oil (SVO) has been used directly as fuel, it is not recommended due to the very high viscosity
and boiling point. This has been shown to reduce engine lifespan and increase maintenance
needs over the long term. [4, 33] These short term sources must be converted into biodiesel to
avoid these issues. Currently, there are a wide range of available oils and fats that can and are
used to produce biodiesel. The choice of which to use comes from scientific reasoning on
their characteristics, but also on economic and social factors as well. In the United States,
soybean oil is the most commonly used source, accounting for 80% of the biodiesel produced
in the country. Canada uses mostly canola oil [7] and in Europe, 84% of their biodiesel
feedstock is rapeseed [9]. Odor and color can also be factors in choosing feedstock, as this
can affect public acceptance [19]. If biodiesel produced from tropical oils in warm climates
are exported to colder climates, they would most likely require additional thinning agents [2].
There is a lot of concern over the overall sustainability of biodiesel especially in feedstock
selection. Choosing vegetable based oil such as soybean and sunflower causes controversy
due to the competition for food sources. Animal fats are very resource intensive to produce.
Waste cooking oils (WCO) are thus receiving more positive opinions because this would
otherwise be disposed of. However, WCO must be pretreated to remove non-oil substances
which offset some of the reduced cost of purchase [7]. There is also not a large enough source
of WCO to supply all potential biodiesel demand. Algae-oil is thus a highly regarded
feedstock because it can be produced quickly to meet demand. There is also high energy
content in algae compared to the other sources. Furthermore, it does not compete with farm
land or water [2]. Algae are prevalent naturally in waste streams from dairy farms and food
processing and sewage ponds [34]. Waste streams and sewage can themselves be used as
feedstock. Angerbauer et al. propose that sewage sludge can be converted to lipids which are
prime sources for biodiesel production [35]. Jatropha seed oil is another feedstock that shows
promise at combating arguments against biodiesel.
Jatropha is one of many inedible vegetable oils and its use would therefore not compete
with food uses [36]. Furthermore, Jatropha grows naturally in many areas that are considered
“developing,” including sub-Saharan Africa, India, South East Asia, and China [16]. Among
its many pros are its ability to survive intertility, drought and is pest-resistant and high yield
[37]. These characteristics allow it to thrive even in wastelands that exist in places like India
which has 80-100 million hectares of wasteland [37]. Table 6 shows fatty acid composition of
Jatropha seed oil.
