Corn ethanol

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

Corn ethanol is ethanol produced from corn that is used as a biomass. Corn ethanol is produced by means of ethanol fermentation and distillation. Corn ethanol is mainly used as an oxygenate in gasoline to produce a low-level blend. To a lesser extent, it is used as fuel for E85 flex-fuel vehicles.[1][2] Corn is the main feedstock used for producing ethanol fuel in the United States.

Production process

An ethanol fuel plant in West Burlington, Iowa.

There are two main types of corn ethanol production: dry milling and wet milling. The products of each type are utilized in different ways.

In the dry milling process the entire corn kernel is ground into flour and referred to as "meal." The meal is then slurried by adding water. Enzymes are added to the mash that convert starch to dextrose, a simple sugar. 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 and transferred and cooled in fermenters. This is where the yeast is added and conversion from sugar to ethanol and carbon dioxide begins.

The entire process takes between 40 and 50 hours, during which time the mash is kept cool and agitated in order to facilitate yeast activity. After the process is complete, everything is 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 and a denaturant such as gasoline is added to render the product undrinkable. With this last addition, the process is complete and the product is ready to ship to gasoline retailers or terminals. The remaining stillage then undergoes a different process to produce a highly nutritious livestock feed. The carbon dioxide released from the process is also utilized to carbonate beverages and to aid in the manufacturing of dry ice.

The process of wet milling takes the corn grain and steeps it in a dilute combination of sulfuric acid and water for 24 to 48 hours in order to separate the grain into many components. The slurry mix then goes through a series of grinders to separate out the corn germ. Corn oil is a by-product of this process and is extracted and sold. The remaining components of fiber, gluten and starch are segregated out using screen, hydroclonic and centrifugal separators.

The gluten protein is dried and filtered to make a corn gluten- meals co-product and is highly sought after by poultry broiler operators as a feed ingredient. The steeping liquor produced is concentrated and dried with the fiber and sold as corn gluten feed to in the livestock industry. The heavy steep water is also sold as a feed ingredient and is used as an environmentally friendly alternative to salt in the winter months. The corn starch and remaining water can then be processed one of three ways: 1) fermented into ethanol, through a similar process as dry milling, 2) dried and sold as modified corn starch, or 3) made into corn syrup.

The production of corn ethanol uses water in two ways – irrigation and processing. There are two types of ethanol processing, wet milling and dry milling, and the central difference between the two processes is how they initially treat the grain. In wet milling, the corn grain is steeped in water, and then separated for processing in the first step. Dry milling, which is more common, requires a different process. According to a report by the National Renewable Energy Laboratory, "Over 80% of U.S. ethanol is produced from corn by the dry grind process.".[3] The dry grind process proceeds as follows:

"Corn grain is milled, then slurried with water to create 'mash.' Enzymes are added to the mash and this mixture is then cooked to hydrolyze the starch into glucose sugars. Yeast ferment these sugars into ethanol and carbon dioxide and the ethanol is purified through a combination of distillation and molecular sieve dehydration to create fuel ethanol. The byproduct of this process is known as distiller's dried grains and solubles (DDGS) and is used wet or dry as animal feed."[4]

Environmental and social issues

Since most U.S. ethanol is produced from corn and the required electricity from many distilleries comes mainly from coal plants, there has been considerable debate on the sustainability of corn-based bio-ethanol in replacing fossil fuels. Controversy and concerns relate to the large amount of arable land required for crops and its impact on grain supply, direct and indirect land use change effects, as well as issues regarding its energy balance and carbon intensity considering the full life cycle of ethanol production, and also issues regarding water use and pollution due to the increase expansion of ethanol production.[4][5][6][7][8][9][10][11][12][13]

The U.S. Department of Energy has published facts stating that current corn-based ethanol results in a 19% reduction in greenhouse gases, and is better for the environment than other gasoline additives such as MTBE.[14]

Ethanol produced today results in fewer greenhouse gas (GHG) emissions than gasoline and is fully biodegradable, unlike some fuel additives.

Others[15] say that ethanol from corn, as a fuel available now, and cellulosic ethanol in the future, are both much better fuels for the environment.[14] Ethanol derived from sugar-beet as used in Europe or sugar-cane as grown in Brazil in industrial scale is generally seen as having a very positive CO2 balance with up to 80% reduction in well-to-wheel CO2.

A University of Nebraska study in 2009 showed corn ethanol directly emits 51% less greenhouse gas than gasoline.[15]

Economic impact of corn ethanol

The Renewable Fuels Association (RFA), the ethanol industry's lobby group, claims that ethanol production does increase 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.[16]

Corn production in 2009 reached over 13.2 billion bushels, and a per acre yield jumped to over 165 bushels per acre.[17]

Alternatives to corn as a feedstock

Remnants from food production such as corn stover could be used to produce ethanol instead of food corn. The use of cellulosic biomass to produce ethanol is a new trend in biofuel production. Fuels from these products are considered second generation biofuels and are considered by some to be a solution to the food verses fuel debate.

See also

References

  1. ↑ "Ethanol Market Penetration". Alternative Fuels and Advanced Vehicles Data Center, US DOE. Retrieved 2006-06-25.
  2. ↑ 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.
  3. ↑ Ethanol Production and Distribution, Alternative Fuels Data Center, US Dept of Energy <http://www.afdc.energy.gov/fuels/ethanol_production.html>
  4. ↑ "Biofuels: The Promise and the Risks, in World Development Report 2008" (PDF). The World Bank. 2008. pp. 70–71. Retrieved 2008-05-04.
  5. ↑ 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. PMID 18258860. doi:10.1126/science.1151861. 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.
  6. ↑ "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
  7. ↑ 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. PMID 18258862. doi:10.1126/science.1152747. 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.
  8. ↑ "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.
  9. ↑ Youngquist, W. Geodestinies, National Book company, Portland, OR, 499p.
  10. ↑ The dirty truth about biofuels
  11. ↑ Deforestation diesel – the madness of biofuel
  12. ↑ Powers, Susan E; Dominguez-Faus, Rosa; Alvarez, Pedro JJ (March 2010). "The water footprint of biofuel production in the USA". Biofuels. Future Science. 1 (2): 255–260. doi:10.4155/BFS.09.20. Retrieved 2010-07-28.
  13. ↑ 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.
  14. 1 2 3 4 5 6 Ethanol Myths and Facts
  15. 1 2 "IANR News: UNL Research: Corn Ethanol Emits 51 Percent Less Greenhouse Gas Than Gasoline". Ianrnews.unl.edu. 22 January 2009. doi:10.1111/j.1530-9290.2008.00105.x. Retrieved 2010-04-04.
  16. ↑ "Ethanol Facts: Agriculture". www.ethanolrfa.org. 12 January 2010. Retrieved 2010-04-04.
  17. ↑ "2009 Crop Year is One for the Record Books, USDA Reports". Nass.usda.gov. 12 January 2010. Retrieved 2010-04-04.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.