Environmental Engineering Reference
In-Depth Information
Is ethanol a good substitute for gasoline?
Ethanol (C 2 H 6 O) is a fuel used mainly in Otto-cycle engines, as a replacement
for gasoline. As opposed to methanol, which is toxic and obtained from coal and
other fossil sources, bioethanol is a very clean and renewable fuel. The traditional
route used to produce ethanol is through sugar fermentation processes and distil-
lation. This route is usually named first-generation technology. Ethanol can also
be obtained from fossil sources by more sophisticated processes (such as the Fis-
cher-Tropsch process, a set of chemical reactions that convert a mixture of carbon
monoxide and hydrogen into liquid hydrocarbons) or acid or enzymatic hydrolys-
is of cellulosic materials, which are considered second-generation technology. The
local benefits of using bioethanol as a fuel are evident in the city of São Paulo,
Brazil, where widespread use of ethanol has reduced emissions of lead, sulfur, car-
bon monoxide, and particulate matter, significantly improving air quality. In addi-
tion, the use of ethanol provides global benefits in the form of reduced CO 2 emis-
sions. Presently ethanol replaces approximately 50% of the gasoline that would be
otherwise used in Brazil.
The Brazilian government encouraged the production of ethanol from sugarcane
and the adaption of Otto-cycle engines to work with “pure” ethanol (hydrated al-
cohol with 96% ethanol and 4% water) or gasohol (a blend of 78% gasoline and
22% anhydrous ethanol). These two types of dedicated engines were recently re-
placed by flex-fuel vehicles (FFVs). By means of electronic sensors, FFV tech-
nology identifies which gasoline-ethanol blend goes through the vehicle injection
system and adjusts the combustion conditions. With the flex vehicle, consumers
have full freedom of choice, mainly determined by the price at the pump. Recent
advances have made the flex technology relatively cheap (amounting to an addi-
tional cost of US$100 or less per automobile), with emissions close to or lower
than those of gasoline. Today more than 95% of cars sold in Brazil are flex-fuel
vehicles.
What are the prospects of biodiesel?
In 1912, Rudolf Diesel, stated that “the use of vegetable oils for engine fuels may
seem insignificant today, but such oils may become, in the course of time, as im-
portant as petroleum and the coal-tar products of the present time.”
Biodiesel production is based on trans-esterification of vegetable oils and fats
through the addition of methanol (or other alcohols) and a catalyst. Glycerol is a
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