Environmental Engineering Reference
In-Depth Information
countries are utilizing biodiesel's lubrication properties to blend with ULSD so that
expensive lubricating additives are not needed [15].
The production of biodiesel is from the transesterification of triglycerides or
by the esterification of fatty acids, which are both found in grease, vegetable
oils, and animal fat. The transesterification of the triglycerides with a short chain
alcohol (such as methanol, ethanol, propanol, or butanol) along with a catalyst,
results in fatty acid esters (biodiesel) and glycerol as a by-product. The generalized
transesterification reaction is given by the following stoichiometry
1[triglyceride]
+
3[alcohol]
↔
3[fatty acid ester (biodiesel)]
+
1[glycerol]
The fatty acids are almost entirely straight chain, mono-carboxylic acids that
typically contain 8-22 even number carbons. Fatty acids are obtained mainly from
soybean, palm kernel, and coconut oils and from the hydrolysis of hard animal fats.
The esterification of the fatty acids with a short chain alcohol along with a catalyst,
results in a fatty acid ester (biodiesel) and water as a by-product. The generalized
esterification reaction is given by the following stoichiometry
1[fatty acid]
+
1[alcohol]
↔
1[fatty acid ester (biodiesel)]
+
1[water]
2.2 Feedstock
The large-scale production of a renewable and environmentally sustainable alter-
native fuel faces several technical challenges that need to be addressed to make
biodiesel feasible and economical. The two main concerns with any renewable fuel
are raw materials and the technologies used for processing. Advances in genetic
modification and other biotechnologies are resulting in new or modified feedstocks
that have significantly increased the yields of alternative fuels, such as genetically
modified
Clostridium
to improve alcohol production [16]. Technological advance-
ments are also being made to convert the feedstocks into fuels by improving
techniques or developing completely new and environmentally friendly approaches
to biofuel production.
There are many feedstocks for biodiesel production such as virgin oils, biomass,
algae, and waste oils, to name a few. Feedstocks also vary with climate and location
and what might be a great source in one place may not be a good source in another.
A considerable amount of research has been done using edible sources of virgin
oils from vegetables, like soybean, rapeseed, sunflower seed, and canola oils, to
produce biodiesel. However, oil with water or high free fatty acid content can result
in the formation of soap as a by-product. Therefore, additional steps must be taken
to prevent soap formation, which requires the utilization of more resources.
The production of biodiesel has increased demand for soybean oil from 1.56 bil-
lion pounds in 2005-2006, to 2.8 billion pounds in 2006-2007 [17]. The increasing
demand for virgin vegetable oil stocks has lead to an increase in price of these oils.
The profitability of biodiesel relies heavily on the cost of its feedstock. The costs of
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