Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
It also is more difficult to chemically convert cellulosic feedstock into sugars. The U.S.
DOE and other government and industry groups are actively supporting research to
develop economically viable processes to convert cellulosic materials into ethanol.
The technology for starch- and sugar-based ethanol production is well-established,
although improvements in efficiency and yields continue to be made. 8 Ethanol can be
produced at dry mills or wet mills. Dry mills are optimized for ethanol production, while
wet mills are designed primarily to produce corn sweeteners but generate ethanol as a
coproduct. Both types of plants produce animal feed and other coproducts as well.
Between 2000 and 2007, the number of ethanol production facilities in the United States
more than doubled, and production capacity tripled, with most of the growth from drymill
plants. In 2008, the ethanol industry included 172 operating plants with a production
capacity of 10.6 billion gallons, with an additional 23 plants with 1.7 billion gallons of
capacity idled (Urbanchuk, 2009).
One cellulosic commercial plant is operating in Georgia, and several more are under
construction. The DOE currently is providing about $500 million to support several smallscale
cellulosic biorefinery projects to demonstrate use of a range of cellulosic feedstock
such as corn stover and other agriculture residues (e.g., wheat straw, rice straw), wood
wastes, municipal solid wastes and energy crops such as switchgrass (U.S. DOE, 2007a,
2008a).
For corn-based ethanol, the majority of feedstock production is in the Midwest, which also
is where most ethanol plants are located. In 2005, 98 percent of corn ethanol feedstock was
shipped to production plants by truck (USDA, 2007). Thus far, the established
infrastructure for food crop distribution has been able to accommodate the transport of
starch- and sugar-based ethanol feedstock to production facilities. While most ethanol
feedstock resources and ethanol plants are in the Midwest, transportation fuel
consumption is highest along the East and West Coasts. Ethanol is generally blended at
the local wholesale terminal for use as E10 or E85, with high concentrations of ethanol
shipped from the point of production (National Commission on Energy Policy, 2009). In
2005, rail accounted for 60 percent of ethanol shipments and truck for 30 percent (USDA,
2007).
8 Brazil, the world’s second-largest ethanol producer behind the United States and the largest
consumer of ethanol for transportation, uses sugar cane as a feedstock. While sugar cane has
significantly higher production yields than corn or cellulose, it is not expected to become a major
source for domestic ethanol production in the United States since there are limited areas where
sugar cane can be grown, and its primary use is for food purposes.
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