Environmental Engineering Reference
In-Depth Information
Ethanol
In 2005, 95 ethanol refineries located in 19 states produced 3.9 billion gallons
of ethanol—an increase of 17 percent over 2004 and 126 percent over 2001. The
United States will consume about 5 billion gallons of ethanol in 2006, according
to the industry's September 2006 projections. Ethanol is blended in 30 percent of
the nation's gasoline and is primarily produced in the Midwest because of the
abundant supply of corn. Ethanol demand is expected to continue to grow as a
result of the national renewable fuels standard,[17] enacted by the Energy Policy
Act of 2005, and the decision of many oil refineries to switch to using ethanol
instead of MTBE as a fuel additive in gasoline that improves its octane and clean-
burning properties.[18]
One of ethanol's biggest challenges is how to cost-effectively expand the
supply of biomass, in addition to corn, to enable the total ethanol market to grow.
DOE scientists are exploring technologies that can cost-effectively use cellulosic
biomass—low-value residues such as wheat straw and corn stover or bio-energy
crops such as fast-growing grasses and trees. Some bio-energy crops, such as
switchgrass, require less fertilizer than corn and can be grown in many U.S.
regions. While cellulosic ethanol requires less fossil energy than corn ethanol on a
total life-cycle basis, capital costs are substantially higher for cellulosic ethanol
plants than for corn ethanol plants. In addition, cellulosic ethanol producers need
to reduce costs for (1) harvesting and handling cellulosic feedstock, (2) enzymes
for converting cellulose to fermentable sugars, and (3) novel fermenting micro-
organisms that can convert these biomass-derived sugars to ethanol. Cellulosic
ethanol currently costs at least twice as much to produce as corn ethanol,
according to DOE officials.
A related challenge is producing sufficient biomass levels without disrupting
current production of food and forest products. In 2005, 1.43 billion bushels of
corn—nearly 13 percent of the U.S. corn crop—were used for ethanol production.
In a 2005 report, the U.S. Department of Agriculture and DOE estimated that the
nation is capable of producing enough ethanol to replace 30 percent of the U.S. oil
consumption by 2030 and still meet food, feed, and export demands.[19]
However, some experts have expressed concern that large-scale diversion of
agricultural resources to generate ethanol could result in higher food prices for
people and livestock. There are also questions about the amount of land that will
be needed to produce higher levels of ethanol, whether vast preserved areas will
be transformed into farmland, water quality issues, and soil sustainability. In
addition, scientists have debated whether ethanol is an effective petroleum
substitute because of the amount of energy needed to produce it—a significant
amount of energy is used because (1) fertilizer made from fossil fuels is used to
