Corn ethanol is

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

produced from

corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...

biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...

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 Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...

. It is debatable whether the production and use of corn ethanol results in lower

greenhouse gas emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and ...

than gasoline. Approximately 45% of U.S. corn croplands are used for

production.

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 The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United States ...

. Overall, 95% of ethanol is produced from corn. Currently, corn ethanol is mainly used in blends with

gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...

to create mixtures such as E10, E15, and E85.

Ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

is mixed into more than 98% of United States gasoline to reduce air pollution. Corn ethanol is used as an oxygenate when mixed with

. E10 and E15 can be used in all engines without modification. However, blends like E85, with a much greater

content, require significant modifications to be made before an engine can run on the mixture without damaging the engine. Some vehicles that currently use E85 fuel, also called flex fuel, include, the Ford Focus,

Dodge Durango The Dodge Durango is a mid-size sport utility vehicle (SUV) produced by Dodge in three generations starting with the 1998 model year. The first two generations were very similar in that both were based on the Dodge Dakota and Ram Pickup, both fe ...

, and Toyota Tundra, among others. The future use of corn ethanol as a main

replacement is unknown. Corn ethanol has yet to be proven to be as cost effective as

due to corn ethanol being much more expensive to create compared to

. Corn ethanol has to go through an extensive milling process before it can be used as a fuel source. One major drawback with corn ethanol, is the energy returned on energy invested ( EROI), meaning the energy outputted in comparison to the energy required to output that energy. Compared to oil, with an 11:1 EROI, corn ethanol has a much lower EROI of 1.5:1, which, in turn, also provides less mileage per gallon compared to gasoline. In the future, as technology advances and oil becomes less abundant, the process of milling may require less energy, resulting in an EROI closer to that of oil. Another serious problem with corn ethanol as a replacement for

, is the engine damage on standard vehicles. E10 contains ten percent

and is acceptable for most vehicles on the road today, while E15 contains fifteen percent

and is usually prohibited for cars built before 2001. However, with the hope to replace

in the future, E85, which contains 85%

, requires engine modification before an engine can last while processing a high volume of

for an extended period of time. Therefore, most older and modern day vehicles would become obsolete without proper engine modifications to handle the increase in corrosiveness from the high volume of

. Also, most gas stations do not offer refueling of E85 vehicles. The

reports that only 3,355 gas stations, out of 168,000, across the United States, offer

refueling for E85 vehicles.

Production process

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 (≈80%) of corn ethanol in the United States is produced by dry milling. In the dry milling process, the entire

corn kernel Corn kernels are the fruits of corn (called maize in many countries). Maize is a grain, and the kernels are used in cooking as a vegetable or a source of starch. The kernel comprise endosperm, germ, pericarp, and tip cap. One ear of corn contai ...

is ground into

flour Flour is a powder made by grinding raw grains, roots, beans, nuts, or seeds. Flours are used to make many different foods. Cereal flour, particularly wheat flour, is the main ingredient of bread, which is a staple food for many cul ...

, or "mash," which is then slurried by adding water. Enzymes are added to the mash to hydrolyze the starch into simple sugars.

Ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...

is added to control the pH and as a nutrient for the

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...

, which is added later. The mixture is processed at high-temperatures to reduce the bacteria levels. The mash is transferred and cooled in fermenters.

Yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...

are added, which ferment the sugars into

and

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

. The entire process takes 40 to 50 hours, during which time the mash is kept cool and agitated to promote

activity. The

is purified through a combination of distillation and dehydration to create fuel ethanol. The mash is then transferred to

distillation column A fractionating column or fractional column is an essential item used in the distillation of liquid mixtures to separate the mixture into its component parts, or fractions, based on the differences in volatilities. Fractionating columns are used in ...

s, where the

is removed from the silage. The

is dehydrated to about 200 proof using a

molecular sieve A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. As a mixture of molecu ...

system. A denaturant such as

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

released from the process is used to carbonate beverages and to manufacture dry ice .

Wet milling

In wet milling, the corn grain is separated into components by steeping in dilute

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...

for 24 to 48 hours. The slurry mix then goes through a series of grinders to separate out the corn germ. The remaining components of fiber, gluten, and starch are segregated using screen, hydroclonic, and centrifugal separators. The

corn starch Corn starch, maize starch, or cornflour (British English) is the starch derived from corn (maize) grain. The starch is obtained from the endosperm of the kernel. Corn starch is a common food ingredient, often used to thicken sauces or sou ...

and remaining water can be fermented into

through a similar process as dry milling, dried and sold as modified

, or made into

corn syrup Corn syrup is a food syrup which is made from the starch of corn (called maize in many countries) and contains varying amounts of sugars: glucose, maltose and higher oligosaccharides, depending on the grade. Corn syrup is used in foods to soft ...

. The gluten protein and steeping liquor are dried to make a

corn gluten meal Corn gluten meal is the principal protein of corn (maize) endosperm consisting mainly of zein and glutelin. It is a byproduct of corn processing that has historically been used as an animal feed. Despite the name, corn gluten does not contain true ...

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 ethanol results in lower

than

and is fully

biodegradable Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegrada ...

, unlike some

fuel additives A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...

such as MTBE.Ethanol Myths and Facts
However, because energy to run many U.S. distilleries comes mainly from

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...

plants, there has been considerable debate on the

sustainability Specific definitions of sustainability are difficult to agree on and have varied in the literature and over time. The concept of sustainability can be used to guide decisions at the global, national, and individual levels (e.g. sustainable livi ...

of corn ethanol in replacing

fossil fuel A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels ma ...

s. Additional controversy relates to the large amount of arable land required for crops and its impact on grain supply and direct and indirect land use change effects. Other issues relate to

pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, th ...

, water use for

irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been devel ...

and processing, energy balance, and emission 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.

Greenhouse gas emissions

Several full life cycle studies have found that corn ethanol reduces

well-to-wheel Life cycle assessment or LCA (also known as life cycle analysis) is a methodology for assessing environmental impacts associated with all the stages of the life cycle of a commercial product, process, or service. For instance, in the case of ...

by up to 50 percent compared to gasoline. However, other research has concluded 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

One of the main controversies involving corn ethanol production is the necessity for arable cropland to grow the corn for ethanol, which is then not available to grow corn for human or animal consumption. In the United States, 40% of the acreage designated for corn grain is used for corn ethanol production, of which 25% was converted to ethanol after accounting for co-products, leaving only 60% of the crop yield for human or animal consumption.

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

production out of 14.99 billion bushels produced in 2020, according to

USDA The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of comme ...

data. According to the U.S. Department of Energy's Alternative Fuels Data Center, "The increased ethanol roductionseems 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 Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn ( North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. T ...

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

. The use of cellulosic biomass to produce

is considered second generation

biofuel Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. According to the United States Energy Information Administration ...

that are considered by some to be a solution to the food versus fuel debate, and has the potential to cut life cycle

by up to 86 percent relative to gasoline.

References

External links

Better Than Corn? Algae Set to Beat Out Other Biofuel Feedstocks
(

Worldwatch Institute The Worldwatch Institute was a globally focused environmental research organization based in Washington, D.C., founded by Lester R. Brown. Worldwatch was named as one of the top ten sustainable development research organizations by Globescan Su ...

). *The End of Cheap Food. (Cover Story). 2007 Economist 385(8558):11-12. *Energy Policy Act of 2005. 2005 Public Law 109-58. *Pimentel, David. 2009 Corn Ethanol as Energy. Harvard International Review 31(2):50-52. *Scully, Vaughan. 2007 Effects of the Biofuel Boom. BusinessWeek Online:26-26. *Waltz, Emily. 2008 Cellulosic Ethanol Booms Despite Unproven Business Models. Nature Biotechnology 26(1):8-9.
Cornstarch Substitute

Martin,Jeremy. 2017. Fueling a Clean Transportation Future.
Union of Concerned Scientists. {{DEFAULTSORT:Corn Ethanol Ethanol fuel Ethanol