Corn is the main feedstock used for producing ethanol fuel in the United States.

Corn ethanol is ethanol produced from corn 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.[1][2] Approximately 45% of U.S. corn croplands are used for ethanol production.[3]

Uses

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 the United 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 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.[5] Corn ethanol is used as an oxygenate when mixed with gasoline. E10 and E15 can be used in all engines without modification. However, blends like E85, with a much greater ethanol content, require significant modifications to be made before an engine can run on the mixture without damaging the engine.[6] Some vehicles that currently use E85 fuel, also called flex fuel, include, the Ford Focus, Dodge Durango, and Toyota Tundra, among others.

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.[6] 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.[7] 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 gasoline, is the engine damage on standard vehicles. E10 contains ten percent ethanol and is acceptable for most vehicles on the road today, while E15 contains fifteen percent ethanol and is usually prohibited for cars built before 2001.[5] However, with the hope to replace gasoline in the future, E85, which contains 85% ethanol, requires engine modification before an engine can last while processing a high volume of ethanol 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 ethanol. Also, most gas stations do not offer refueling of E85 vehicles. The United States Department of Energy reports that only 3,355 gas stations, out of 168,000, across the United States, offer ethanol refueling for E85 vehicles.[8]

Production process

An ethanol fuel plant in West Burlington, Iowa.

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.[9]

Dry milling

The vast majority (≈80%) of corn ethanol in the United States is produced by dry milling.[10] In the dry milling process, the entire corn kernel is ground into flour, or "mash," which is then slurried by adding water.[11] Enzymes are added to the mash to hydrolyze the starch into simple sugars. 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 fermenters. 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).[12] The carbon dioxide 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 for 24 to 48 hours.[13] 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 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 ethanol results in lower greenhouse gas emissions than gasoline and is fully biodegradable, unlike some fuel additives such as MTBE.[14] 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 fossil fuels. 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, water use for irrigation and processing, energy balance, and emission intensity for the full life cycle of ethanol production.[15][16][17][18][19][20][21][22][23][24]

Greenhouse gas emissions

Corn-processing plant near Columbus, Nebraska.

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.[14][25][26][27] 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[28]

Ethanol-blended fuels currently in the market – whether E10 or E85 – meet stringent tailpipe emission standards.[14]

Croplands

Corn vs Ethanol production in the United States
  Total corn production (bushels) (left)
  Corn used for Ethanol fuel (bushels) (left)
  Percent of corn used for Ethanol (right)

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.[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]

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.[31] Corn production in 2009 reached over 13.2 billion bushels, and a per acre yield jumped to over 165 bushels per acre.[32] 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.[33] 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."[33] 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.[14]

See also

References

  1. ↑ Smil, Vaclav (2017). Energy Transitions: Global and National Perspectives. Santa Barbara, California: Praeger, an imprint of ABC-CLIO, LLC. p. 162. ISBN 978-1-4408-5324-1. OCLC 955778608.
  2. ↑ Conca, James. "It's Final -- Corn Ethanol Is of No Use". Forbes. Retrieved 1 April 2019.
  3. ↑ "USDA ERS – Feedgrains Sector at a Glance". ers.usda.gov. Retrieved 15 December 2022.
  4. ↑ "Alternative Fuels Data Center: Maps and Data – U.S. Corn for Fuel Ethanol, Feed and Other Use". afdc.energy.gov. Retrieved 16 April 2019.
  5. 1 2 3 "Alternative Fuels Data Center: Ethanol Fuel Basics". afdc.energy.gov. Retrieved 16 April 2019.
  6. 1 2 "Corn Ethanol Use in the Midwest". large.stanford.edu. Retrieved 16 April 2019.
  7. ↑ Cleveland, Cutler J.; O’Connor, Peter; Hall, Charles A. S.; Guilford, Megan C. (October 2011). "A New Long Term Assessment of Energy Return on Investment (EROI) for U.S. Oil and Gas Discovery and Production". Sustainability. 3 (10): 1866–1887. doi:10.3390/su3101866.
  8. ↑ "Alternative Fuels Data Center: Ethanol Fueling Station Locations". afdc.energy.gov. Retrieved 16 April 2019.
  9. ↑ Bothast, R. J.; Schlicher, M. A. (2014). "Biotechnological processes for conversion of corn into ethanol". Applied Microbiology and Biotechnology. 67 (1): 19–25. doi:10.1007/s00253-004-1819-8. ISSN 0175-7598. PMID 15599517. S2CID 10019321.
  10. ↑ Ethanol Production and Distribution, Alternative Fuels Data Center, US Dept of Energy <http://www.afdc.energy.gov/fuels/ethanol_production.html>
  11. ↑ Verser, D. W.; Eggeman, T. J. Process for producing ethanol from corn dry milling. US7888082B2. https://patents.google.com/patent/US7888082B2/en
  12. ↑ Section, Government of Alberta, Alberta Agriculture and Forestry, Livestock and Crops Division, Crop Research and Extension Branch, Livestock and Crop Research Extension (1 November 2011). "Feeding Distillers Dried Grains with Solubles (DDGS) to Pigs". www1.agric.gov.ab.ca. Retrieved 23 November 2018.{{cite web}}: CS1 maint: multiple names: authors list (link)
  13. ↑ Jackson, David S.; Shandera, Donald L. (1995), "Corn Wet Milling: Separation Chemistry and Technology", Advances in Food and Nutrition Research, Elsevier, 38: 271–300, doi:10.1016/s1043-4526(08)60085-6, ISBN 9780120164387, PMID 15918293
  14. 1 2 3 4 Ethanol Myths and Facts Archived 15 December 2010 at the Wayback Machine
  15. ↑ "Biofuels: The Promise and the Risks, in World Development Report 2008" (PDF). The World Bank. 2008. pp. 70–71. Retrieved 4 May 2008.
  16. ↑ Timothy Searchinger; et al. (29 February 2008). "Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change". Science. 319 (5867): 1238–1240. Bibcode:2008Sci...319.1238S. doi:10.1126/science.1151861. PMID 18258860. S2CID 52810681. 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.
  17. ↑ "Another Inconvenient Truth" (PDF). Oxfam. 28 June 2008. Archived from the original (PDF) on 19 August 2008. Retrieved 6 August 2008.Oxfam Briefing Paper 114, figure 2 pp.8
  18. ↑ Fargione; Hill, J.; Tilman, D.; Polasky, S.; Hawthorne, P.; et al. (29 February 2008). "Land Clearing and the Biofuel Carbon Debt". Science. 319 (5867): 1235–1238. Bibcode:2008Sci...319.1235F. doi:10.1126/science.1152747. PMID 18258862. S2CID 206510225. Originally published online in Science Express on 7 February 2008. There are rebuttals to these findings for assuming a worst-case scenario.
  19. ↑ "Proposed Regulation to Implement the Low Carbon Fuel Standard. Volume I: Staff Report: Initial Statement of Reasons" (PDF). California Air Resources Board. 5 March 2009. Retrieved 26 April 2009.
  20. ↑ Youngquist, W. Geodestinies, National Book company, Portland, OR, 499p.
  21. ↑ "The dirty truth about biofuels". Archived from the original on 4 December 2009. Retrieved 30 July 2010.
  22. ↑ Deforestation diesel – the madness of biofuel
  23. ↑ Powers, Susan E; Dominguez-Faus, Rosa; Alvarez, Pedro JJ (March 2010). "The water footprint of biofuel production in the USA". Biofuels. 1 (2): 255–260. doi:10.4155/BFS.09.20. S2CID 130923687.
  24. ↑ United States National Research Council, Committee on Water Implications of Biofuels Production in the United States (2008). Water Implications of Biofuels Production in the United States. The National Academy Press, Washington, D.C. ISBN 978-0-309-11361-8.
  25. ↑ Farrell, Alexander E.; Plevin, Richard J.; Turner, Brian T.; Jones, Andrew D.; O'Hare, Michael; Kammen, Daniel M. (2006). "Ethanol Can Contribute to Energy and Environmental Goals". Science. 311 (5760): 506–508. Bibcode:2006Sci...311..506F. doi:10.1126/science.1121416. ISSN 0036-8075. PMID 16439656. S2CID 16061891.
  26. ↑ Daniel., Sperling (2009). Two billion cars : driving toward sustainability. Gordon, Deborah, 1959–. Oxford: Oxford University Press. ISBN 9780199704095. OCLC 302414399.
  27. ↑ Liska, Adam L.; Yang, Haishun S.; Bremer, Virgil R.; Klopfenstein, Terry J.; Walters, Daniel T.; Erickson, Galen E.; Cassman, Kenneth G. (2009). "Improvements in Life Cycle Energy Efficiency and Greenhouse Gas Emissions of Corn‐Ethanol". Journal of Industrial Ecology. 13: 58–74. doi:10.1111/j.1530-9290.2008.00105.x. S2CID 18630452.
  28. ↑ Lark, Tyler; Hendricks, Nathan (2022). "Environmental outcomes of the US Renewable Fuel Standard". Proceedings of the National Academy of Sciences. 119 (9). doi:10.1073/pnas.2101084119. PMC 8892349. PMID 35165202.
  29. ↑ Brown, Lester Russell (2003). Plan B: Rescuing a Planet Under Stress and a Civilization in Trouble. W. W. Norton & Company. ISBN 9780393325232.
  30. ↑ Mumm, Rita H; Goldsmith, Peter D; Rausch, Kent D; Stein, Hans H (2014). "Land usage attributed to corn ethanol production in the United States: sensitivity to technological advances in corn grain yield, ethanol conversion, and co-product utilization". Biotechnology for Biofuels. 7 (1): 61. doi:10.1186/1754-6834-7-61. ISSN 1754-6834. PMC 4022103. PMID 24725504. 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.
  31. ↑ "Ethanol Facts: Agriculture". ethanolrfa.org. 12 January 2010. Retrieved 4 April 2010.
  32. ↑ "2009 Crop Year is One for the Record Books, USDA Reports". Nass.usda.gov. 12 January 2010. Archived from the original on 14 January 2010. Retrieved 4 April 2010.
  33. 1 2 "Alternative Fuels Data Center: Maps and Data – Corn Production and Portion Used for Fuel Ethanol". afdc.energy.gov. Retrieved 29 August 2019.
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