D2_RW
Ethanol: It’s Effect on the Environment
Energy is a substantial part of everyday life. Everyone needs energy to move
forward. Whether that energy is food that keeps humans alive or energy that powers cities
and cars. Without a doubt, fuel energy is crucial for the world. We need fuel for
transportation, industrial power, and many other important reasons. One molecule that
can define fuel in this modern day is ethanol. Simply put, ethanol is just an alcohol, but
there are many commercial, and even recreational uses for ethanol. One prime example is
alcoholic beverages; ethanol is the alcohol found in them (1). On the topic of renewable
energy, ethanol is the only clean burning liquid fuel available to replace the fuel used in
cars. In 2012, 13.3 billion gallons of ethanol was produced in the US, which eliminated
the need of for more than 465 million gallons of imported, foreign oil (2). In addition,
this domestic production of ethanol provided more than 383,000 jobs within the
agricultural, manufacturing and energy service sectors (2). Although many countries in
the world use ethanol as a fuel source, there are economic, social, and political factors to
why ethanol cannot be a sustainable energy source for the US. The purpose of this essay
is to examine the chemistry behind ethanol and its synthesis, and more importantly,
discuss the pros and cons of using ethanol as a renewable energy source in the US.
The molecular formula for ethanol is CH3CH2OH. Ethanol is a two-carbon
alcohol that consists of methyl group attached to a methylene group, which is attached to
the end hydroxyl group. The figure below shows the molecular structure of ethanol (3).
The synthesis of ethanol was one of the first biotechnologies in human history.
Aforementioned, ethanol was consumed as an alcohol during ancient times. Proof of
distilling alcohol was discovered when scientists analyzed dried residue from 9,000-year
old pots from China (1). There are two widely used methods to make ethanol. One
method is for making ethanol for use as an industrial feedstock or solvent and the second
method is for use in alcoholic beverages and fuel. The first method is ethylene hydration
where ethanol is made by the acid-catalyzed hydration of ethylene. This reaction is
illustrated below by figure 2.
An acid like sulfuric acid can catalyze the above reaction. In the second method, ethanol
is produced by fermentation of yeast. In short, fermentation is the culturing of yeast under
specific thermal conditions so that alcohol is produced. An example of this is the reaction
of certain species of yeast with sugar. The sugar is metabolized in reduced-oxygen
conditions, which yields ethanol and carbon dioxide products. This particular reaction is
shown in the figure 3 below.
When making alcohol, allowing grains to germinate to produce the enzyme
amylase, which converts the starch into sugar, usually obtain the sugar. Likewise, in the
production of ethanol for fuel, the starch from corn is harvested and converted into sugar,
and a combination of amylase and sulfuric acid conditions can accomplish great yields of
ethanol (2). This process can be shown in figure 4 below.
During ethanol fermentation, glucose and other sugars in the corn (or sugarcane
or other crops) are converted into ethanol and carbon dioxide. However, ethanol
fermentation is not 100% selective due to the other side products such acetic acid, glycols
and many other products that are formed to a considerable extent and need to be removed
during the purification of the ethanol. The fermentation takes place in aqueous solution
and the resulting solution after fermentation has an ethanol content of around 15%. The
ethanol is subsequently isolated and purified by a combination of adsorption and
distillation techniques. During combustion ethanol reacts with oxygen to produce carbon
dioxide, water, and heat. Ethanol fermentation also known as alcoholic fermentation is a
biological process that is performed by yeasts in the absence of oxygen and considered an
anaerobic process.
Ethanol is most commonly used to power automobiles, farm tractors, boats and
airplanes. Ethanol consumption in an engine is approximately 51% higher than for
gasoline since the energy per unit volume of ethanol is 34% lower than for gasoline. The
higher compression ratios in an ethanol-only engine allow for increased power output and
better fuel economy than could be obtained with lower compression ratios.
Vehicles that use E85 have to meet similar requirement such as tailpipe emission
standards as other light duty vehicles. However, when using E85, these flex-fuel vehicles
may have lower emissions of some pollutants than conventional gasoline-fueled vehicles.
Ethanol contains soluble and insoluble contaminants. These soluble contaminants,
halide ions such as chloride ions, have a large effect on the gradual destruction of alcohol
fuels. Halide ions increase corrosion in two ways; they chemically attack oxide films on
several metals causing pitting corrosion, and they increase the conductivity of the fuel.
Increased electrical conductivity promotes electric, galvanic, and ordinary corrosion in
the fuel system. Soluble contaminants, such as aluminum hydroxide, itself a product of
corrosion by halide ions, clog the fuel system over time.
Ethanol is hygroscopic, which has the ability to absorb water vapor directly from
the atmosphere. However, because absorbed water dilutes the fuel value of the ethanol
and may cause phase separation of ethanol-gasoline blends, containers of ethanol fuels
must be kept tightly sealed. This high ability to be mixed with water indicates that
ethanol cannot be efficiently shipped through modern pipelines over long distances.
Mechanics also have encountered increased cases of damage to small engines in
particular the carburetor due to the increased water retention by ethanol in fuel.
Furthermore, ethanol is considered to be better and less harmful for the environment
than gasoline. Ethanol-fueled vehicles produce lower carbon monoxide and carbon
dioxide emissions, and the same or lower levels of hydrocarbon and oxides of nitrogen
emissions. Also, ethanol production supports farmers and creates domestic jobs. Also,
because ethanol is produced domestically, from domestically grown crops, it reduces
U.S. dependence on foreign oil and increases the nation’s energy independence.
Overall, the underlying question of the century in terms of energy is what the US
will do once the supply of crude oil disappears. The US’s heavy dependence on foreign
oil paired with a strong culture of driving has made the transition to alternative energies a
challenge. However, products in the US that require energy are being geared towards
using alternative sources of energy. A prime example of this is the use of hybrid and
electric cars. The use of electricity to power an automobile could greatly reduce the need
for foreign oil. This brings up the question of why ethanol has not been used in the US as
its’ main fuel source. Countries like Brazil have been praised for their groundbreaking
transportation services and use of ethanol to power their vehicles.
So why hasn’t the US pushed for the use of ethanol as a primary fuel source?
Firstly, the amount of ethanol needed to satisfy the amount of drivers there are in the US
would be in the hundreds of billions of gallons. In 2013 alone, the US consumed roughly
133 billion gallons of fuel, which averages to 366 million gallons of fuel a day (3).
Secondly, the majority of cars in the US are not made for ethanol fuel so the demand for
high-ethanol based fuels is low. However, ethanol is the main fuel source in the Midwest
US where there is an abundance of corn crops. Another significant factor in ethanol
production is land use. Ethanol fuel critics contend that producing ethanol as a primary
fuel source will drive world food prices up and cause drastic shortages in corn crops for
food. However, ethanol fuel advocates counter this contention by stating that more than
93% of all corn grown in the US is never fed to people, but is used as livestock feed and
ethanol production (4). In addition, American farmers grow more corn than people can
purchase; there is generally an annual surplus of corn in the US (4). In regards to the
environment, the expansion of acreage for ethanol would cause new carbon emissions,
habitat loss, and water-quality degradation (2).
In conclusion, ethanol is an excellent way to fight air pollution from vehicles, but
environmental studies and economic analysis show that it is not a viable, nor sustainable
energy source. Moreover, there is no fuel available at scale today that is similar to
ethanol's ability in improving the overall environmental quality compared to gasoline.
However, from its biodegradable nature to reductions in greenhouse gas and tailpipe
emissions, ethanol provides a tool that considers all the environmental concerns without
requiring an entirely new way for goods and people to get from one place to another. For
now, gasoline and hybrid-electric cars are still the forefront for energy. Maybe in the near
future ethanol will become a more significant, and even primary source of alternative
energy.
References
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Simpson, Tom. "Biofuels: The Past, Present, and a New Vision for the
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U.S. Energy Information Administration - EIA - Independent Statistics and
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03 Mar. 2014
Wilson, Jeff. "U.S. Corn-Surplus Seen Larger Than Expected on Early
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"Chemistry in its element - ethanol." Royal Society of Chemistry. N.p., 2014.
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