Corn ethanol is ethanol produced from Maize biomass and is the main source of ethanol fuel in the United States, mandated to be blended with gasoline in the Renewable Fuel Standard. Corn ethanol is produced by ethanol fermentation and distillation. It is debatable whether the production and use of corn ethanol results in lower greenhouse gas emissions than gasoline.
Uses
Since 2001, corn ethanol production has increased by more than several times.
Out of 9.50 billions of bushels of corn produced in 2001, 0.71 billions of bushels were used to produce corn ethanol. Compared to 2018, out of 14.62 billions of bushels of corn produced, 5.60 billion bushels were used to produce corn ethanol, reported by the United States Department of Energy. Overall, 94% of ethanol in the United States is produced from corn.
Currently, corn ethanol is mainly used in blends with gasoline to create mixtures such as E10, E15, and E85. Ethanol is mixed into more than 98% of United States gasoline to reduce air pollution.
The future use of corn ethanol as a main gasoline replacement is unknown. Corn ethanol has yet to be proven to be as cost effective as gasoline due to corn ethanol being much more expensive to create compared to gasoline.
Beyond its role as a transportation fuel, ethanol from corn can be dehydrated to ethylene or coprocessed in fluid catalytic cracking units. A 2025 cradle to gate life cycle assessment reported lower greenhouse gas emissions for such bioethylene pathways than for fossil-derived ethylene production.
Production process
Biofuels can be produced through biological or thermochemical routes, with bioethanol among the most common.
Recent plant upgrades have incorporated energy saving measures such as heat integration, improved distillation efficiency, and advanced enzymes that increase starch to ethanol conversion rates.
Examples of such measures include replacing natural gas with biomass derived syngas, installing combined heat and power systems, and capturing CO₂ from fermentation or distillation.
There are two main types of corn ethanol production: dry milling and
wet milling, which differ in the initial grain treatment method and co-products.
Dry milling
The vast majority (≈90%) of corn ethanol in the United States is produced by dry milling.
[Ethanol Production and Distribution, Alternative Fuels Data Center, US Dept of Energy ] In the dry milling process, the entire
corn kernel is ground into
flour, or "mash,"
/ref>
are added to the mash to hydrolyze the starch into
.
Ammonia is added to control the pH and as a nutrient for the
yeast, which is added later. The mixture is processed at high-temperatures to reduce the bacteria levels. The mash is transferred and cooled in
.
Yeast are added, which ferment the sugars into
ethanol and
carbon dioxide. The entire process takes 40 to 50 hours, during which time the mash is kept cool and agitated to promote
yeast activity. The mash is then transferred to distillation columns, where the
ethanol is removed from the
silage. The
ethanol is dehydrated to about 200 proof using a
molecular sieve system. A denaturant such as
gasoline is added to render the product undrinkable. The product is then ready to ship to gasoline retailers or terminals. The remaining
silage is processed into a highly nutritious
livestock feed known as distiller's dried grains and solubles (DDGS).
The
carbon dioxide released from the process can be used to carbonate beverages and to manufacture
dry ice .
Wet milling
In
Wet-milling, the
Maize is separated into components by steeping in dilute
sulfurous acid for 24 to 48 hours.
The slurry mix then goes through a series of grinders to separate out the corn
Cereal germ. The remaining components of fiber,
gluten, and starch are segregated using screen, hydroclonic, and centrifugal separators. The
corn starch and remaining water can be fermented into
ethanol through a similar process as dry milling, dried and sold as modified
corn starch, or made into
corn syrup. The
gluten protein and steeping liquor are dried to make a corn gluten meal that is sold to the livestock industry. The heavy steep water is also sold as a feed ingredient and used as an alternative to salt in the winter months.
Corn oil is also extracted and sold.
Environmental issues
Corn based ethanol is classified as a first generation biofuel produced from edible crops; later generations derive from lignocellulosic feedstocks or algae.
Corn ethanol results in lower greenhouse gas emissions than
gasoline and is fully
Biodegradation, unlike some
fuel additives such as MTBE.
[ Ethanol Myths and Facts ] However, because energy to run many U.S. distilleries comes mainly from
coal plants, there has been considerable debate on the
sustainability of corn ethanol in replacing
. Additional controversy relates to the large amount of arable land required for crops and its impact on grain supply and
ILUC. Other issues relate to
pollution, water use for
irrigation and processing, energy balance, and emission
carbon intensity for the full life cycle of ethanol production.
[ Originally published online in Science Express on 7 February 2008. See Letters to Science by Wang and Haq. There are critics to these findings for assuming a worst-case scenario.][Oxfam Briefing Paper 114, figure 2 pp.8][ Originally published online in Science Express on 7 February 2008. There are rebuttals to these findings for assuming a worst-case scenario.][Youngquist, W. Geodestinies, National Book company, Portland, OR, 499p.][ Deforestation diesel – the madness of biofuel]
Greenhouse gas emissions
.|alt=|400x400px]]Several full life cycle studies have found that corn ethanol reduces
well-to-wheel greenhouse gas emissions by up to 50 percent compared to gasoline.
A 2022 Argonneled life cycle analysis estimated the current U.S. corn ethanol carbon intensity at about 52.4 g CO₂e/MJ. The study found that combining efficiency measures, fuel switching (e.g., syngas or renewable natural gas in place of natural gas), and carbon capture could reduce the CI to as low as −18.4 g CO₂e/MJ, including land use change.
The analysis also accounted for credits from co products such as distillers dried grains with solubles (DDGS), which displace conventional animal feed and thereby reduce overall life cycle greenhouse gas emissions.
However, more recent research based on an analysis of data from the first eight years of the US Renewable Fuel Standard's implementation suggests that corn ethanol produces more carbon emissions per unit of energy than gasoline, when factoring in fertilizer use and land use change.
Ethanol-blended fuels currently in the market – whether E10 or E85 – meet stringent tailpipe emission standards.
Croplands and land use
[[File:Corn vs Ethanol production.webp|thumb|300px|Corn vs ethanol production in the United States
]]
One of the main controversies involving corn ethanol production is the necessity for Arable land to grow the corn for ethanol, which is then not available to grow corn for human or animal consumption.
Growing corn to fuel internal combustion vehicles is a highly inefficient use of land. A solar farm generating electricity to power an electric vehicle would power around 85 times as much distance as corn ethanol grown on the same area.
Economic impact of corn ethanol
The Renewable Fuels Association (RFA), the ethanol industry's lobbying group, claims that ethanol production increases the price of corn by increasing demand. The RFA claims that ethanol production has positive economic effect for US farmers, but it does not elaborate on the effect for other populations where field corn is part of the staple diet. An RFA lobby document states that "In a January 2007 statement, the USDA Chief Economist stated that farm program payments were expected to be reduced by some $6 billion due to the higher value of a bushel of corn.
Corn production in 2009 reached over 13.2 billion bushels, and a per acre yield jumped to over 165 bushels per acre.
In the United States, 5.05 billion bushels of corn were used for ethanol production out of 14.99 billion bushels produced in 2020, according to
USDA data.
According to the U.S. Department of Energy's Alternative Fuels Data Center, "The increased ethanol production seems to have come from the increase in overall corn production and a small decrease in corn used for animal feed and other residual uses. The amount of corn used for other uses, including human consumption, has stayed fairly consistent from year to year."
This does not prove there was not an impact on food supplies: Since U.S. corn production doubled (approximately) between 1987 and 2018, it is probable that some cropland previously used to grow other food crops is now used to grow corn. It is also possible or probable that some marginal land has been converted or returned to agricultural use. That may have negative environmental impacts.
Alternative biomass for ethanol
Remnants from food production such as
corn stover could be used to produce ethanol instead of food corn. Ethanol derived from sugar-beet as used in Europe or sugar-cane in Brazil has up to 80% reduction in
well-to-wheel carbon dioxide. The use of cellulosic biomass to produce
ethanol is considered second generation
biofuel that are considered by some to be a solution to the food versus fuel debate, and has the potential to cut life cycle greenhouse gas emissions by up to 86 percent relative to gasoline.
See also
External links
