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In its pure or neat form, ethanol is a colorless, waterlike
liquid with a mild odor which boils at 78C. (172F.) and freezes at -1l2C. (-170F.). When burned it produces a pale blue flame with no soot and much energy, making it an ideal fuel. Ethanol mixes readily with water
and is frequently used as a solvent and as an ingredient when making hundreds of other chemicals.
Ethanol is a product of fermentation, a process by which many organisms derive energy from sugar. This process
is comparable to the respiration of food nutrients in many animals and plants. In fermentation, however, energy is obtained when sugar is changed to ethanol and carbon dioxide.
Because of the way the
hydroxide (OH) is bonded to the carbon, ethanol has no basic or acidic properties. When dissolved in water it is neutral and has a pH of 7.
From Corn (Starch) to Ethanol by Fermentation/Changing corn to
ethanol by fermentation involves several distinct steps. Starch in corn, primarily Amylose Amylopectin (80%), are built from thousands of complex sugar molecules. These must be broken down into simple sugars or
monosaccharides before fermentation can occur. In earlier times, this was accomplished by chewing the corn and allowing the saliva enzymes to naturally break down the starch. Today, this is achieved by cooking the
corn and adding the enzymes alpha amylase and gluco amylase. (Enzymes are complex chemicals which function as catalysts to bring about specific chemical changes in other materials.) New and improved methods are
being explored to more effectively do this conversion, a process often referred to as saccharification.
Once a simple sugar is obtained, a single celled plant yeast, Saccharomyes sp., is added, which then
grows and brings about fermentation. This step has been known throughout history. The process of releasing the energy from the sugar is similar to that of cellular respiration, except for the final two steps of the
process as outlined below:
In fermentation, the yeast releases ethanol and carbon dioxide. In respiration, continuation of the breakdown yields carbon dioxide, water, and energy. In fermentation, the ethanol
retains much of the energy that was originally present in the sugar and, while inefficient for the yeast, explains why ethanol is an excellent fuel.
Although ethanol can also be produced from ethylene (C2H4)
from the petroleum industry, the fermentation of food grains is still the primary source. At this point, corn is considered the most practical product in the United States to ferment.
The Commercial Production of Ethanol
Although ethanol production takes various forms (including the fermentation of sweet fruit juice to wine, for instance), most of the United States production is in
large industrial plants, most of which are located in the Midwest. Nearly one half of the nationÍs supply is produced in Illinois.
Changing the sugars and starches in corn kernels to ethanol is a complex
process and has become well established as a mix of technologies which includes microbiology, chemistry, and engineering. Greatly simplified, it involves:
a. mechanically grinding the corn as finely as practical
b. stirring while adding water and an enzyme to create a slurry (while maintaining a pH of 7 by adding sodium hydroxide or sulfuric acid)
c. adding
additional enzymes and heat to convert starch molecules to complex sugars (dextrins)
d. cooling and adding other enzymes to break down the complex sugars into simple sugars
e. adding yeast to convert the sugars to ethanol through fermentation
f. removing the ethanol from the mash by distillation or evaporation.
At every step, specific acidity levels, pressures, and temperatures
must be maintained. In industry this takes place in huge factories under carefully controlled conditions using highly developed technologies.
Ethanol Technology
Ethanol production in which a
product from Midwest farms is used as a material from which to produce fuel which improves living standards is an illustration of how science, technology, agriculture, and industry are interwoven. The ethanol plants
receive the vast quantities of corn they need by truck, rail, or barge (whichever is least costly). Here the corn is cleaned, finely ground, and blown into gigantic tanks where it is mixed into a slurry of cornmeal
and water. Enzymes are added to the slurry and precise acidity levels and temperatures are maintained, causing the starches in the corn to break down, first into complex sugars and finally into simple sugars.
New technologies have also greatly changed the fermentation process. Until recently several days were required for the yeast to work in each batch to produce ethanol. A new faster and more cost efficient technology,
continuous fermentation, now alleviates many of the problems of the batch system.
Geneticists and other plant scientists are also involved. They have successfully developed strains of yeast which can convert
even greater percentages of the starch to ethanol.
After fermentation, the ethanol is removed from the resulting mix of ethanol, water, yeast, and residue and purified by distillation, a process which takes
advantage of ethanol's low boiling point, 78C. When the mix is heated to a temperature a bit higher than this, the ethanol evaporates and is subsequently recaptured as a gas and condensed. Additional chemicals,
redistillation processes, and molecular sieves are used to further purify the ethanol.
Although distillation uses large amounts of energy (much of which comes from coal) technological advances are being made
which greatly reduce the amount of energy needed for this stage. These advances help to further reduce the costs of producing ethanol.
That's Not All
Ethanol is not the only valuable product
that comes from this process. Most of the substance of the corn kernel remains and has great value in the production of food for people, livestock feed, and various chemicals. A bushel of corn (56 Ibs.) used in
ethanol manufacture yields the following coproducts:
1.6 lbs. corn oil
3.0 lbs. corn gluten meal
13.0 lbs. corn gluten feed
12.5 lbs. carbon dioxide
The first of these coproducts are used in
producing food for human consumption and high protein livestock feed. For instance, the 1.6 lbs. of corn oil from a bushel of corn is equivalent to 2 lbs. of margarine. The carbon dioxide is used as a refrigerant,
in carbonated beverages, to help vegetable crops to grow more rapidly in greenhouses, and to flush oil wells. In effect, only the starch of the corn (carbon, hydrogen, and oxygen) goes into the ethanol.
ENERGY IN - ENERGY OUT
Much energy is required at each step of the way in the production of ethanol beginning with seedbed preparation for planting the corn and ending with that energy needed to transport
the ethanol to the place where it is blended with gasoline.
Although the net amount of energy that is actually gained as a result of ethanol production is hotly debated, a big advantage results from having a
liquid which is readily used in automobiles as the end product.
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