Environmental Engineering Reference
In-Depth Information
requires pretreatment before processing. Enzymatic saccharification followed by
fermentation and fermentation using cellulolytic microorganisms are the two main
processing techniques used for the production of cellulosic ethanol.
In this chapter, we will examine the current state of the art in the production of
biodiesel, biobutanol and cellulose ethanol, respectively.
2 Biodiesel
2.1 Background
Over the past decade, interest in biodiesel use has grown due to the increasing price
of petroleum and the effect of carbon emissions on climate change. Biodiesel is
a non-toxic and biodegradable alternative fuel, which can be used in conjunction
with or as a substitute for petroleum diesel fuel. The first account for the production
of biodiesel was in 1937 by the Belgian professor G. Chavanne of the University
of Brussels, who applied for a patent (Belgian Patent 422,877) for the “Procedure
for the transformation of vegetable oils for their uses as fuels” [12]. The chemical
structure of biodiesel is that of a fatty acid alkyl ester, which is clean burning [13].
Biodiesel contains no polycyclic aromatic hydrocarbons, and emits very little sulfur
dioxide, carbon monoxide, carbon dioxide, and particulates, which greatly reduces
health risks when compared to petroleum diesel.
The first diesel engine was created in 1893 by a German mechanical engineer,
Rudolph Diesel. The diesel engine is an internal compression-ignition engine that
uses the compression of the fuel to cause ignition, instead of a spark plug for gaso-
line engines. As a result, a higher compression ratio is required for a diesel engine,
which for the same power output (when compared to a gasoline engine), is more
efficient and uses less fuel. The higher compression ratio requires the diesel engine
to be built stronger so it can handle the higher pressure; consequently, the longevity
of a diesel engine is generally higher than its gasoline equivalent. These vehicles
therefore require less maintenance and repair overall, thus saving money [14]. In
the European markets, over 40% of new car sales are diesel. This is due to a large
influx of highly efficient diesel engines used in small cars.
An advantage of biodiesel is that current compression-ignition (diesel) engines,
15 years old or newer, can operate with pure biodiesel, or any blend, with no engine
modifications. Older engine systems may require replacement of fuel lines and
other rubber components in order to operate on biodiesel. The current infrastruc-
ture for petroleum diesel fuel can be utilized for biodiesel, thus reducing costs and
widespread implementation criteria. The Environmental Protection Agency (EPA)
in 2006 limited sulfur emission in diesel fuels to 15 ppm. New trucks and buses with
diesel engines, from model year 2007, are now required to use only ultra low sul-
fur diesel (ULSD) with new emissions control equipment. The higher sulfur levels
aided in diesel fuel lubrication; however, biodiesel is oxygenated and therefore is
naturally a better lubricant and has similar material compatibility to ULSD. Many
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