Ethanol is a colorless, volatile, flammable liquid that is the intoxicating agent
in liquors and is also used as a fuel or solvent. Ethanol is also called ethyl
alcohol or grain alcohol.
Ethanol is the most important member of a large group of organic compounds that
are called alcohol. Alcohol is an organic compound that has one or more hydroxyl
(OH) groups attached to a carbon atom. Alcohol is shown as: C-O-H or C-OH.
What is attached to the carbon at the three remaining bonds or locations
determines the particular kind of alcohol. Ethanol has hydrogen present at
two sites while the remaining site holds another carbon atom. This carbon
atom, in turn, holds three more hydrogen atoms.
It may be shown as:
H H
| |
H-C-C-O-H or CH3CH2OH
| |
H H
In its pure form, ethanol is a colorless clear liquid with a mild characteristic
odor which boils at 78C.(172F.) and freezes at -112C. (-170F.). The molecular
weight is 46.07 One gallon of 190 proof ethanol weighs 6.8 pounds. Ethanol has no
basic or acidic properties. When burned ethanol produces a pale blue flame
with no residue and considerable energy, making it an ideal fuel. Ethanol
mixes readily with water and with most organic solvents. It is also useful as
a solvent and as an ingredient when making many other substances including
perfumes, paints, lacquer, and explosives.
HOW IT IS MADE
Ethanol is a product of fermentation. Fermentation is a sequence of reactions
which release energy from organic molecules in the absence of oxygen. In this
application of fermentation, energy is obtained when sugar is changed to
ethanol and carbon dioxide. All beverage ethanol and more than half of
industrial ethanol is made by this process.
Changing corn to ethanol by fermentation takes many steps. Starch in corn
must be broken down into simple sugars before fermentation can occur. In
earlier times, this was done by chewing the corn. This allowed the salivary
enzymes to naturally break down the starch. Today, this is achieved by
cooking the corn and adding the enzymes alpha amylase and gluco amylase.
These enzymes function as catalysts to speed up the chemical changes.
Once a simple sugar is obtained, yeast is added. Yeast is a single-celled fungi
which feeds on the sugar and causes the fermentation. As the fungi feeds
on the sugar, it produces alcohol (ethanol) and carbon dioxide. In
fermentation, the ethanol retains much of the energy that was originally in the
sugar, and explains why ethanol is an excellent fuel.
The fermentation reaction is represented by the simple equation:
C6H12O6 -- 2 CH3CH2OH + 2 CO2
COMMERCIAL PRODUCTION
Most of the ethanol production in the United States is made in 50 production
facilities in 20 different states. Most of these plants are located in the Midwest.
Changing the starch in kernels of corn to sugar and changing sugar to ethanol
is a complex process and requires a mix of technologies that include
microbiology, chemistry and engineering.
Ethanol is produced from corn by using one of two standard processes: wet-milling
or dry-milling. Dry-milling plants cost less to build and produce higher yields of
ethanol, but the value of co-products is less.
Most of the ethanol plants in the country utilize a dry-milling process. The major
steps of dry-milling are outlined below:
1. Milling: After the corn (barley or wheat) is cleaned, it will pass
first through hammer mills which grind it into a fine powder.
2. Liquefaction: The meal will then be mixed with water and an enzyme
(alpha-amylase), and will pass through cookers where the starch is
liquefied. A pH of 7 is maintained by adding sulfuric acid or sodium
hydroxide. Heat is applied to enable liquefaction. Cookers with a
high temperature stage (120-150 degrees Celsius) and a lower
temperature holding period (95C) will be used. The high temperatures
reduce bacteria levels in the mash.
3. Saccharification: The mash from the cookers will be cooled and the
enzyme gluco-amylase will be added to convert starch molecules to
fermentable sugars (dextrose).
4. Fermentation: Yeast will be added to the mash to ferment the sugars to
ethanol and carbon dioxide. Using a continuous process, the fermenting
mash will flow or cascade, through several fermenters until the mash is
fully fermented and leaves the tank. In a batch fermentation process,
the mash stays in one fermenter for about 48 hours.
5. Distillation: The fermented mash, now called "beer" will contain about
10% alcohol, as well as all the non-fermentable solids from the corn and
the yeast cells. The mash will then be pumped to the continuous flow,
multi-column distillation system where the alcohol will be removed from
the solids and water. The alcohol will leave the top of the final column at
about 96% strength, and the residue mash, called stillage, will be
transferred from the base of the column to the co-product processing
area.
6. Dehydration: The alcohol will then pass through a dehydration system
where the remaining water will be removed. Most plants use a molecular
sieve to capture the last bit of water in the ethanol. The alcohol at
this stage is called anhydrous (pure, without water) ethanol and is
approximately 200 proof.
7. Denaturing: Ethanol that will be used for fuel is then denatured with a
small amount (2-5%) of some product, like gasoline, to make it unfit
for human consumption.
The wet-milling operation is more elaborate because the grain must be separated into
its components. After milling, the corn is heated in a solution of water and sulfur
dioxide for 24 to 48 hours to loosen the germ and the hull fiber. The germ is then
removed from the kernel, and corn oil is extracted from the germ. The remaining
germ meal is added to the hulls and fiber to form corn gluten feed. A high-protein
portion of the kernel called gluten is separated and becomes corn gluten meal
which is used for animal feed. In wet-milling, only the starch is fermented, unlike
dry-milling, when the entire mash is fermented.
TECHNOLOGY
The production of ethanol is an example of how science, technology, agriculture, and
industry must work in harmony to change a farm product into a fuel. Ethanol plants
receive the large quantities of corn they need by truck, rail, or barge. The corn
is cleaned, ground, and blown into large tanks where it is mixed into a slurry of
cornmeal and water. Enzymes are added and exact acidity levels and temperatures
are maintained, causing the starch in the corn to break down, first into complex
sugars then into simple sugars.
New technologies have changed the fermentation process. In the beginning it took
several days for the yeast to work in each batch. A new faster and less costly
method of continuous fermentation has been developed.
Plant scientists and geneticists are also involved. They have been successful in
developing strains of yeast that can convert greater percentages of starch to
ethanol.
After fermentation, the ethanol is removed from the mix of ethanol, water, yeast,
and residue. It is then purified through distillation. The distilling process
takes advantage of the low boiling point (78C.) of ethanol. When the temperature of
the mix is increased slightly higher than the boiling point, the ethanol evaporates.
It is then captured as a gas vapor and condensed back to a liquid. Other chemicals
are added and molecular sieves are used to purify the ethanol.
Advances in technology are being made to further reduce the large amounts of
energy needed for distillation. Technologies expected to be adopted include:
steeping with gas injection of sulfur dioxide, membrane saccharification,
high-tolerance yeast, yeast immobilization, bacterial fermentation, and
pervaporation. These advances help to reduce the costs and make producing
ethanol more economical.
WHAT'S IN A BUSHEL OF CORN?
Each bushel of corn can produce up to 2.5 gallons of ethanol fuel. Only the
starch from the corn is used to make ethanol. Most of the substance of the
corn kernel remains, leaving the protein and valuable co-products to be used
in the production of food for people, livestock feed, and various chemicals.
For example, that same bushel of corn (56 lbs.) used in ethanol manufacturing
can also produce the following:
| The wet-milling process: | The dry-milling process: |
| 31.5 pounds of starch | 10 one-lb. boxes of cereal |
| or | and |
| 33 lbs. of sweetner | 15 lbs. of brewer grits (enough for 1 gal. of beer) |
| or | and |
| 2.5 gal. fuel ethanol | 10 eight oz. packages of Cheese Curls |
| and | and |
| 12.4 lbs. of 21% protein feed | 1 lb. of pancake mix |
| and | and |
| 3.0 lbs. of 60% gluten meal | 22 lbs. of hominy feed for livestock |
| and | and |
| 1.5 lbs. of corn oil | 0.7 lbs. of corn oil |
| and | and |
| 17 lbs. of carbon dioxide | 17 lbs. of carbon dioxide |
The corn oil is used in producing food for human consumption. For example,
1.5 lbs of corn oil from a bushel of corn is equivalent to 2 lbs of margarine.
The 21% protein feed is used in making high protein livestock feed. 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.
Only the starch of the corn (carbon, hydrogen, and oxygen) is used to make ethanol.
ENERGY
One of the most controversial issues relating to ethanol is the question of
"net energy" of ethanol production. According to the Institute for Local
Self Reliance research in 1995, the production of ethanol from corn is a
positive net energy generator. If corn farmers use state-of-the-art, energy
efficient farming techniques, and ethanol plants use state-of-the-art production
processes, then the amount of energy contained in a gallon of ethanol and the
other co-products is more than twice the energy used to grow the corn and
convert it into ethanol. This study indicated an industry average net energy
gain of 1.38 to 1. The industry best existing production net energy ratio was
2.09 to 1. If farmers and industry were to use all the best technologies and
practices the net energy ratio would be 2.51 to 1. The following chart
indicates the percentage gains and gains in BTU's.
Energy Gain in Making Ethanol from Corn
BTU's Percentage Ratio
Industry average 30,589 38% 1.38:1
Industry best 62,857 109% 2.09:1
State-of-the-art 72,413 151% 2.51:1
Current research prepared by Argonne National Laboratory (a U.S. Department
of Energey Laboratory), indicates a 38% gain in the overall energy input/output
equation for the corn-to-ethanol process. That is, if 100 BTU's of energy is used
to plant corn, harvest the crop, transport it, etc., 138 BTU's of energy is
available in the fuel ethanol. Corn yields and processing technologies have improved
significantly over the past 20 years and they continue to do so, making ethanol
production less and less energy intensive.
STUDY QUESTIONS
True-False:
Circle T for each True statement or F for each False statement.
T F 1. Ethyl alcohol is another name for ethanol.
T F 2. Ethanol is used as a fuel or solvent.
T F 3. One disadvantage of ethanol is that it is hard to
mix with other chemicals.
T F 4. Ethanol burns with a yellow-reddish flame.
T F 5. Ethanol is made using a fermentation process.
T F 6. Fermentation releases energy by changing sugar into
carbon dioxide and ethanol.
T F 7. Starch in corn must be changed to sugar before
fermentation can take place.
T F 8. Yeast feeds on sugar which produces carbon dioxide
and water.
T F 9. Most ethanol is produced in the southern United
States.
T F 10. It takes more energy to produce one gallon of
ethanol than the energy in one gallon of ethanol.
T F 11. In the wet milling process, all of the mash is
fermented.
Short Answer
- Fill in the blanks with the best answer to complete each statement below.
1. One bushel of corn produces ________ gallons of ethanol.
2 - 5. List 4 other products that are produced during the manufacturing of ethanol.
6. The part of a kernel of corn that is used to make ethanol is called
____________.
7. The ethanol manufacturing industry's average net energy gain is ________ to one.
8. Each BTU used to produce a gallon of gasoline could be used to produce ________
BTU's of ethanol.
9. The boiling point of ethanol is _______ ° Fahrenheit.
Sequence
Indicate the major steps used in a dry-milling process by placing a number in the
blank provided to indicate the proper steps in order. (The first step is
number 1, etc.)
______ a. Liquefaction
______ b. Fermentation
______ c. Milling
______ d. Dehydration
______ e. Saccharification
______ f. Distillation
______ g. Denaturing
PROJECTS
Complete an experiment in fermentation. This experiment will test different foods
and determine how heat affects fermentation.
FERMENTATION EXPERIMENT
Ethanol is made from a variety of plant substances including corn, sugar cane, wood.
The process used to make ethanol is fermentation. Fermentation was discovered many
years ago when bubbles or foam was formed while making wine and beer. Studies by
Louis Pasteur described fermentation as changes caused by yeasts growing in the
absence of air. Fermentation is an energy yielding process caused by enzymes
(yeasts) in which fuel molecules such as glucose (sugar) are broken down in the
absence of oxygen. You will test different substances while observing for
fermentation (bubbling). State your findings in the space provided.
Materials: 8 or more pkgs. of yeast ice
measuring spoons 4 clear glass, half-liter containers
stirrers heating element
flour, salt, sugar, vinegar
Fermenting Foods
1. Empty a pkg. of yeast into each half-liter (1 pint) beaker of warm water. Stir
for 1 minute.
2. Add 10 ml (2 tsp.) of flour to each beaker and stir again.
3. Add 5 ml (1 tsp.) of salt to the first beaker, 5 ml of sugar to the second
beaker, 5 ml of vinegar to the third, and do nothing to the fourth. Stir again.
4. Wait 5 minutes. Record your observations.
Beaker 1_____________________________________________________
Beaker 2_____________________________________________________
Beaker 3_____________________________________________________
Beaker 4_____________________________________________________
5. Wait 15 minutes and record your observations.
Beaker 1_____________________________________________________
Beaker 2_____________________________________________________
Beaker 3_____________________________________________________
Beaker 4_____________________________________________________
6. Let the solutions sit overnight and record your observations.
Beaker 1_____________________________________________________
Beaker 2_____________________________________________________
Beaker 3_____________________________________________________
Beaker 4_____________________________________________________
Questions:
1. What is the evidence that reactions are going on in any of the containers?
2. How are these observations related to fermentation?
3. State any conclusions about which of the substances tested was most helpful
to yeast fermentation?
Changing Temperatures
1. In this part you will observe the effect of different temperatures of water on
fermentation. The teacher will prepare boiling water for the first beaker.
Fill the second beaker with warm water (just slightly warmer than skin
temperature). Fill the third beaker with cold tap water. Fill the fourth
beaker with ice water.
2. Empty one packet of yeast into each beaker and stir to dissolve. Add 10 ml
of flour and 5 ml of sugar to each jar and stir again.
3. Wait 5 minutes. Record your observations.
Beaker 1_____________________________________________________
Beaker 2_____________________________________________________
Beaker 3_____________________________________________________
Beaker 4_____________________________________________________
4. Wait 15 minutes. Record your observations.
Beaker 1_____________________________________________________
Beaker 2_____________________________________________________
Beaker 3_____________________________________________________
Beaker 4_____________________________________________________
Questions:
1. Were there any conditions under which fermentation did not proceed or went very
slowly? What were they? Explain each one.
2. State any conclusions about what temperature is best for yeast-flour-sugar
fermentation.
If time permits, try different combinations of yeast, food, and temperatures to
determine the best mixture for fermentation.
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