Ethanol
Ethanol is a renewable transportation fuel
primarily made from starch crops, such as corn. It is also
made from sugar beets and cane or cellulosic materials, such
as fast-growing trees and grasses. Nearly one-third of U.S.
gasoline contains ethanol in a low-level blend to reduce air
pollution.
Read more about Ethanol as alternative fuel - click
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Facts
about Ethanol
E85 (85% ethanol, 15% gasoline) is considered
an alternative fuel in the USA.
U.S.-produced ethanol is primarily produced
from corn or sugar crops by dry-mill or wet-mill processing.
Although wet-mill facilities were common in the industry's
early days, dry-mill facilities now account for more than
80% of industry capacity. Between 2000 and 2007, the number
of ethanol plants more than doubled and production capacity
tripled in the United States. Most of that growth came from
dry-mill plants because they are dedicated and optimized for
the production of ethanol.
Dry Mills
Dry-mill ethanol plants are optimized to
produce ethanol with carbon dioxide (CO2) and animal feed
as co-products. In these facilities, the corn is ground into
coarse flour. Next, water and enzymes are added and the mixture
is "cooked." Yeast is then added, and the mixture
is fermented. This "mash" is sent to the distillation
system and molecular sieves to remove the water to produce
200-proof ethanol. The ethanol is denatured (usually with
gasoline) to make it unfit for human consumption and sent
to ethanol storage tanks.
The solids and liquids remaining after distillation
are generally recombined for sale as high-protein animal feed
(known as wet distillers grains with solubles or WDGS). Some
facilities also incorporate dryers to remove the moisture
from the WDGS and to extend its shelf life. This dried co-product
is called dried distillers grain.
The CO2 co-product can be released to the
atmosphere but is commonly captured and marketed to the food
processing industry for use in carbonated beverages or the
production of dry ice.
Wet Mills
Wet-mill plants primarily produce corn sweeteners,
along with ethanol and several other co-products (such as
corn oil, animal feed, starch). In these mills, the first
step is to soak the corn grain in hot water to separate the
protein and starch. The product is then coarsely ground, and
the germ is separated to be processed into corn oil. Next,
the remaining slurry, which contains gluten, starch, and fiber,
is finely ground and separated so the fiber can be blended
into animal feed and the starch/gluten mixture can be further
processed. The starch is then dried to make corn starch or
processed to produce sugars, corn syrup, and beverage sweeteners.
The sugars are then fermented to produce ethanol.
Above information from http://www.eere.energy.gov
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