Corn ethanol isethanol produced fromcornbiomass and is the main source ofethanol fuel in the United States, mandated to be blended with gasoline in theRenewable Fuel Standard. Corn ethanol is produced byethanol fermentation anddistillation. It is debatable whether the production and use of corn ethanol results in lowergreenhouse gas emissions than gasoline.[1][2] Approximately 45% of U.S. corncroplands are used forethanol production.[3]
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Since 2001, corn ethanol production has increased by more than several times.[4] 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 theUnited States Department of Energy. Overall, 94% of ethanol in the United States is produced from corn.[5]
Currently, corn ethanol is mainly used in blends withgasoline to create mixtures such asE10,E15, andE85.Ethanol is mixed into more than 98% of United States gasoline to reduce air pollution.[5] Corn ethanol is used as anoxygenate when mixed withgasoline. E10 andE15 can be used in all engines without modification. However, blends like E85, with a much greaterethanol content, require significant modifications to be made before an engine can run on the mixture without damaging the engine.[6] Some vehicles that currently useE85 fuel, also calledflex fuel, include, theFord Focus,Dodge Durango, andToyota Tundra, among others.[citation needed]
The future use of corn ethanol as a maingasoline replacement is unknown. Corn ethanol has yet to be proven to be as cost effective asgasoline due to corn ethanol being much more expensive to create compared togasoline.[6] Corn ethanol has to go through an extensivemilling 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 11:1EROI, corn ethanol has a much lowerEROI of 1.5:1, which, in turn, also provides less mileage per gallon compared to gasoline.[7] In the future, as technology advances and oil becomes less abundant, the process ofmilling may require less energy, resulting in anEROI closer to that of oil. Another serious problem with corn ethanol as a replacement forgasoline, is the engine damage on standard vehicles. E10 contains ten percentethanol and is acceptable for most vehicles on the road today, whileE15 contains fifteen percentethanol and is usually prohibited for cars built before 2001.[5] However, with the hope to replacegasoline in the future,E85, which contains 85%ethanol, requires engine modification before an engine can last while processing a high volume ofethanol for an extended period of time. Therefore, most older and modern day vehicles would become obsolete without proper engine modifications to handle the increase incorrosiveness from the high volume ofethanol. Also, most gas stations do not offer refueling of E85 vehicles. TheUnited States Department of Energy reports that only 3,355 gas stations, out of 168,000, across the United States, offerethanol refueling forE85 vehicles.[8]
There are two main types of corn ethanol production:dry milling andwet milling, which differ in the initial grain treatment method and co-products.[9]
The vast majority (≈90%) of corn ethanol in the United States is produced bydry milling.[10] In thedry milling process, the entirecorn kernel is ground intoflour, or "mash," which is then slurried by adding water.[11]Enzymes are added to the mash to hydrolyze the starch intosimple sugars.Ammonia is added to control thepH and as a nutrient for theyeast, which is added later. The mixture is processed at high-temperatures to reduce the bacteria levels. The mash is transferred and cooled infermenters.Yeast are added, which ferment the sugars intoethanol andcarbon dioxide. The entire process takes 40 to 50 hours, during which time the mash is kept cool and agitated to promoteyeast activity. The mash is then transferred todistillation columns, where theethanol is removed from thesilage. Theethanol is dehydrated to about 200 proof using amolecular sieve system. Adenaturant such asgasoline is added to render the product undrinkable. The product is then ready to ship to gasoline retailers or terminals. The remainingsilage is processed into a highly nutritiouslivestock feed known as distiller's dried grains and solubles (DDGS).[12] Thecarbon dioxide released from the process is used tocarbonate beverages and to manufacturedry ice .[citation needed]
Inwet milling, thecorn grain is separated into components by steeping in dilutesulfurous acid for 24 to 48 hours.[13] The slurry mix then goes through a series of grinders to separate out the corngerm. The remaining components of fiber,gluten, and starch are segregated using screen, hydroclonic, and centrifugal separators. Thecorn starch and remaining water can be fermented intoethanol through a similar process asdry milling, dried and sold as modifiedcorn starch, or made intocorn syrup. Thegluten protein and steeping liquor are dried to make acorn 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.[citation needed]
Corn ethanol results in lowergreenhouse gas emissions thangasoline and is fullybiodegradable, unlike somefuel additives such asMTBE.[14] However, because energy to run many U.S. distilleries comes mainly fromcoal plants, there has been considerable debate on thesustainability of corn ethanol in replacingfossil fuels. Additional controversy relates to the large amount of arable land required for crops and its impact ongrain supply anddirect and indirect land use change effects. Other issues relate topollution, water use forirrigation and processing,energy balance, and emissionintensity for thefull life cycle of ethanol production.[15][16][17][18][19][20][21][22][23][24]
.JPG)
Severalfull life cycle studies have found that corn ethanol reduceswell-to-wheelgreenhouse gas emissions by up to 50 percent compared to gasoline.[14][25][26][27] However, more recent research based on an analysis of data from the first eight years of the USRenewable Fuel Standard’s implementation suggests that corn ethanol produces more carbon emissions per unit of energy than gasoline, when factoring in fertilizer use andland use change.[28]
Ethanol-blended fuels currently in the market – whether E10 or E85 – meet stringent tailpipe emission standards.[14]
One of the main controversies involving corn ethanol production is the necessity forarable cropland to grow the corn for ethanol, which is thennot available to grow corn for human or animal consumption.[29] 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.[30]
Growing corn to fuel internal combustion vehicles is a highly inefficient use of land. Asolar farm generating electricity to power an electric vehicle would power around 85 times as much distance as corn ethanol grown on the same area.[31]
TheRenewable 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.[32] Corn production in 2009 reached over 13.2 billion bushels, and a per acre yield jumped to over 165 bushels per acre.[33]In the United States, 5.05 billion bushels of corn were used forethanol production out of 14.99 billion bushels produced in 2020, according toUSDA data.[34] 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."[34]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.[citation needed]
Remnants from food production such ascorn 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 inwell-to-wheelcarbon dioxide. The use ofcellulosic biomass to produceethanol is considered second generationbiofuel that are considered by some to be a solution to the food versus fuel debate, and has the potential to cut life cyclegreenhouse gas emissions by up to 86 percent relative to gasoline.[14]
{{cite web}}: CS1 maint: multiple names: authors list (link)Although 40.5% of corn grain was channeled to ethanol processing in 2011, only 25% of US corn acreage was attributable to ethanol when accounting for feed co-product utilization.