Corn ethanol

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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. Corn ethanol is produced by ethanol fermentation and distillation. Corn ethanol results in lower greenhouse gas emissions than gasoline and is fully biodegradable, but environmental concerns ; approximately 40.5% of the U.S. corn croplands are used for ethanol production.[1]

Uses[edit]

Corn ethanol is mainly added as an oxygenate to gasoline to produce a low-level blend used in motor vehicles. To a lesser extent, it is used as fuel for E85 flex-fuel vehicles.[2][3]

Production process[edit]

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.[4]

Dry milling[edit]

The vast majority (≈80%) of corn ethanol in the United States is produced by dry milling.[5] In the dry milling process, the entire corn kernel is ground into flour, or "mash," which is then slurried by adding water.[6] 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 ethanol is purified through a combination of distillation and dehydration to create fuel ethanol. The mash is then transferred to distillation columns, where the ethanol is removed from the stillage. 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 stillage is processed into a highly nutritious livestock feed known as distiller's dried grains and solubles (DDGS).[7] The carbon dioxide released from the process is used to carbonate beverages and for dry ice manufacturing.

Wet milling[edit]

In wet milling, the corn grain is separated into components by steeping in dilute sulfuric acid for 24 to 48 hours.[8] 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[edit]

Corn ethanol results in lower greenhouse gas emissions than gasoline and is fully biodegradable, unlike some fuel additives such as MTBE.[9] 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.[10][11][12][13][14][15][16][17][18][19]

Greenhouse gas emissions[edit]

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.[9][20][21][22] Ethanol-blended fuels currently in the market – whether E10 or E85 – meet stringent tailpipe emission standards.[9]

Croplands[edit]

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.[23] 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.[1]

Economic impact of corn ethanol[edit]

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.[24] Corn production in 2009 reached over 13.2 billion bushels, and a per acre yield jumped to over 165 bushels per acre.[25]

Alternative biomass for ethanol[edit]

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.[9]

See also[edit]

References[edit]

  1. ^ a b 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.
  2. ^ "Ethanol Market Penetration". Alternative Fuels and Advanced Vehicles Data Center, US DOE. Retrieved 2006-06-25.
  3. ^ Goettemoeller, Jeffrey; Adrian Goettemoeller (2007). Sustainable Ethanol: Biofuels, Biorefineries, Cellulosic Biomass, Flex-Fuel Vehicles, and Sustainable Farming for Energy Independence. Prairie Oak Publishing, Maryville, Missouri. p. 42. ISBN 978-0-9786293-0-4.
  4. ^ Bothast, R. J.; Schlicher, M. A. (2014). "Biotechnological processes for conversion of corn into ethanol" (PDF). Applied Microbiology and Biotechnology. 67 (1): 19–25. doi:10.1007/s00253-004-1819-8. ISSN 0175-7598. PMID 15599517.
  5. ^ Ethanol Production and Distribution, Alternative Fuels Data Center, US Dept of Energy <http://www.afdc.energy.gov/fuels/ethanol_production.html>
  6. ^ Verser, D. W.; Eggeman, T. J. Process for producing ethanol from corn dry milling. US7888082B2. https://patents.google.com/patent/US7888082B2/en
  7. ^ Section, Government of Alberta, Alberta Agriculture and Forestry, Livestock and Crops Division, Crop Research and Extension Branch, Livestock and Crop Research Extension (2011-11-01). "Feeding Distillers Dried Grains with Solubles (DDGS) to Pigs". www1.agric.gov.ab.ca. Retrieved 2018-11-23.
  8. ^ Jackson, David S.; Shandera, Donald L. (1995), "Corn Wet Milling: Separation Chemistry and Technology", Advances in Food and Nutrition Research, Elsevier, pp. 271–300, doi:10.1016/s1043-4526(08)60085-6, ISBN 9780120164387, retrieved 2018-11-23
  9. ^ a b c d Ethanol Myths and Facts Archived 15 December 2010 at the Wayback Machine.
  10. ^ "Biofuels: The Promise and the Risks, in World Development Report 2008" (PDF). The World Bank. 2008. pp. 70–71. Retrieved 2008-05-04.
  11. ^ 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. doi:10.1126/science.1151861. PMID 18258860. Retrieved 2008-05-09. 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.
  12. ^ "Another Inconvenient Truth" (PDF). Oxfam. 28 June 2008. Archived from the original (PDF) on 19 August 2008. Retrieved 2008-08-06.Oxfam Briefing Paper 114, figure 2 pp.8
  13. ^ 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. doi:10.1126/science.1152747. PMID 18258862. Retrieved 2008-08-06. Originally published online in Science Express on 7 February 2008. There are rebuttals to these findings for assuming a worst-case scenario.
  14. ^ "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 2009-04-26.
  15. ^ Youngquist, W. Geodestinies, National Book company, Portland, OR, 499p.
  16. ^ The dirty truth about biofuels
  17. ^ Deforestation diesel – the madness of biofuel
  18. ^ 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.[permanent dead link]
  19. ^ 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.
  20. ^ 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. doi:10.1126/science.1121416. ISSN 0036-8075. PMID 16439656.
  21. ^ Daniel., Sperling, (2009). Two billion cars : driving toward sustainability. Gordon, Deborah, 1959-. Oxford: Oxford University Press. ISBN 9780199704095. OCLC 302414399.
  22. ^ 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.
  23. ^ Brown, Lester Russell (2003). Plan B: Rescuing a Planet Under Stress and a Civilization in Trouble. W. W. Norton & Company. ISBN 9780393325232.
  24. ^ "Ethanol Facts: Agriculture". www.ethanolrfa.org. 12 January 2010. Retrieved 2010-04-04.
  25. ^ "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.

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