Corn ethanol is

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

produced from

corn Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout Poaceae, grass that produces cereal grain. It was domesticated by indigenous peoples of Mexico, indigenous peoples in southern Mexico about 9,000 years ago ...

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

and is the main source of

ethanol fuel in the United States The United States became the world's largest producer of ethanol fuel in 2005. The U.S. produced 15.8 billion U.S. liquid gallons of ethanol fuel in 2019, up from 13.9 billion gallons (52.6 billion liters) in 2011, and from 1.62 billion gall ...

, mandated to be blended with gasoline in the Renewable Fuel Standard. Corn ethanol is produced by

ethanol fermentation Ethanol fermentation, also called alcoholic fermentation, is a biological process which converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products. Because yeasts perform this ...

and

distillation Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixt ...

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

greenhouse gas emissions Greenhouse gas (GHG) emissions from human activities intensify the greenhouse effect. This contributes to climate change. Carbon dioxide (), from burning fossil fuels such as coal, petroleum, oil, and natural gas, is the main cause of climate chan ...

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 energy production, the research and development of nuclear power, the military's nuclear w ...

. Overall, 94% of ethanol in the United States is produced from corn. Currently, corn ethanol is mainly used in blends with

gasoline Gasoline ( North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When for ...

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

Ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

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

oxygenate In the liquid fuel industry, oxygenates are hydrocarbon-derived fuel additives containing at least one oxygen atom to promote complete combustion. Absent oxygenates, fuel combustion is usually incomplete, and the exhaust stream pollutes the air ...

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 A flexible-fuel vehicle (FFV) or dual-fuel vehicle (colloquially called a flex-fuel vehicle) is an alternative fuel vehicle with an internal combustion engine designed to run on more than one fuel, usually gasoline blended with either ethanol o ...

, include, the

Ford Focus The Ford Focus is a compact car (C-segment in Europe) manufactured by Ford Motor Company from 1998 until 2025. It was created under Alexander Trotman's Ford 2000 plan, which aimed to globalize model development and sell one compact vehicle worl ...

Dodge Durango The Dodge Durango is a mid-size SUV produced by Dodge starting with the 1998 model year. The first two generations were very similar in that both were based on the Dodge Dakota and Dodge Ram, both featured a body-on-frame construction and both ...

, and

Toyota Tundra The Toyota Tundra is a full-size pickup truck manufactured in the United States by the Japanese manufacturer Toyota since May 1999. The Tundra was the second full-size pickup to be built by a Japanese manufacturer (the first was the Toyota T100 ...

, 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 Milling may refer to: * Milling (minting), forming narrow ridges around the edge of a coin * Milling (grinding), breaking solid materials into smaller pieces by grinding, crushing, or cutting in a mill * Milling (machining), a process of using ro ...

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

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 (≈90%) 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 Maize, 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 (grain), germ, pericarp, and tip cap. ...

is ground into

flour Flour is a powder made by Mill (grinding), grinding raw grains, List of root vegetables, roots, beans, Nut (fruit), nuts, or seeds. Flours are used to make many different foods. Cereal flour, particularly wheat flour, is the main ingredie ...

, or "mash," which is then slurried by adding water.

Enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s are added to the mash to hydrolyze the starch into

simple sugar Monosaccharides (from Greek '' monos'': single, '' sacchar'': sugar), also called simple sugars, are the simplest forms of sugar and the most basic units ( monomers) from which all carbohydrates are built. Chemically, monosaccharides are poly ...

Ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

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 (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

, 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 (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

are added, which ferment the sugars into

and

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

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

activity. The mash is then transferred to distillation columns, where the

is removed from the

silage Silage is fodder made from green foliage crops which have been preserved by fermentation (food), fermentation to the point of souring. It is fed to cattle, sheep and other ruminants. The fermentation and storage process is called ''ensilage'', ' ...

. The

is dehydrated to about 200 proof using a

molecular sieve A molecular sieve is a material with pores of uniform size comparable to that of individual molecules, linking the interior of the solid to its exterior. These materials embody the molecular sieve effect, in which molecules larger than the pore ...

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

is processed into a highly nutritious

livestock feed Fodder (), also called provender (), is any agriculture, agricultural foodstuff used specifically to feed domesticated livestock, such as cattle, domestic rabbit, rabbits, sheep, horses, chickens and pigs. "Fodder" refers particularly to food ...

known as distiller's dried grains and solubles (DDGS). The

released from the process is used to carbonate beverages and to manufacture

dry ice Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and Sublimation (phase transition), sublimes directly from the solid state to the gas ...

Wet milling

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

sulfurous acid Sulfuric(IV) acid (United Kingdom spelling: sulphuric(IV) acid), also known as sulfurous (UK: sulphurous) acid and thionic acid, is the chemical compound with the chemical formula, formula . Raman spectroscopy, Raman spectra of solutions o ...

for 24 to 48 hours. The slurry mix then goes through a series of grinders to separate out the corn

germ Germ or germs may refer to: Science * Germ (microorganism), an informal word for a pathogen * Germ cell, cell that gives rise to the gametes of an organism that reproduces sexually * Germ layer, a primary layer of cells that forms during embry ...

. The remaining components of fiber,

gluten Gluten is a structural protein naturally found in certain Cereal, cereal grains. The term ''gluten'' usually refers to the elastic network of a wheat grain's proteins, gliadin and glutenin primarily, that forms readily with the addition of water ...

, and starch are segregated using screen, hydroclonic, and centrifugal separators. The

corn starch Cornflour, cornstarch, maize starch, or corn starch (American English) is the starch derived from corn (maize) grain. The starch is obtained from the endosperm of the seed, kernel. Corn starch is a common food ingredient, often used to thick ...

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 that is made from the starch of corn/maize and contains varying amounts of sugars: glucose, maltose and higher oligosaccharides, depending on the grade. Corn syrup is used in foods to soften Mouthfeel, texture, add vol ...

. The

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 Corn oil (North American) or maize oil (British) is oil extracted from the germ of corn (maize). Its main use is in cooking, where its high smoke point makes refined corn oil a valuable frying oil. It is also a key ingredient in some margarin ...

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 such as

MTBE Methyl ''tert''-butyl ether (MTBE), also known as ''tert''-butyl methyl ether, is an organic compound with a structural formula (CH3)3COCH3. MTBE is a volatile, flammable, and colorless liquid that is sparingly soluble in water. Primarily used as ...

.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 Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

plants, there has been considerable debate on the

sustainability Sustainability is a social goal for people to co-exist on Earth over a long period of time. Definitions of this term are disputed and have varied with literature, context, and time. Sustainability usually has three dimensions (or pillars): env ...

of corn ethanol in replacing

fossil fuel A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geolog ...

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 harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...

, water use for

irrigation Irrigation (also referred to as watering of plants) 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 bee ...

and processing, energy balance, and emission

intensity Intensity may refer to: In colloquial use * Strength (disambiguation) *Amplitude * Level (disambiguation) * Magnitude (disambiguation) In physical sciences Physics *Intensity (physics), power per unit area (W/m2) *Field strength of electric, m ...

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

by up to 50 percent compared to gasoline. 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 Land use is an umbrella term to describe what happens on a parcel of land. It concerns the benefits derived from using the land, and also the land management actions that humans carry out there. The following categories are used for land use: for ...

. Ethanol-blended fuels currently in the market – whether E10 or E85 – meet stringent tailpipe emission standards.

Croplands and land use

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. Growing corn to fuel internal combustion vehicles is a highly inefficient use of land. A

solar farm A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system (PV system) designed for the supply of merchant power. They are different from most building ...

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 The Renewable Fuels Association (RFA) represents the ethanol industry promoting policies, regulations, and research and development initiatives that will lead to the increased production and use of ethanol fuel. First organized in 1981, RFA serve ...

(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 an United States federal executive departments, executive department of the Federal government of the United States, United States federal government that aims to meet the needs of commerc ...

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 Corn stover consists of the leaves, stalks, and cobs of corn (maize) (''Zea mays'' ssp. ''mays'' L.) plants left in a field after harvest. Such stover makes up about half of the yield of a corn crop and is similar to straw from other cere ...

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

. 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 (energy), biomass, rather than by the very slow natural processes involved in the formation of fossil fuels such as oil. Biofuel can be produced from plants or from agricu ...

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 S ...

). *The End of Cheap Food. (Cover Story). 2007 Economist 385(8558):11–12. *Energy Policy Act of 2005. 2005 Public Law . *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 The Union of Concerned Scientists (UCS) is a nonprofit science advocacy organization based in the United States. The UCS membership includes many private citizens in addition to professional scientists. Anne Kapuscinski, Professor of Environment ...

. {{DEFAULTSORT:Corn Ethanol Ethanol fuel Ethanol Maize products