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Corn (Maize) for Bioethanol as a Fuel Source
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Corn (Zea Mays) or Maize is a popular crop source for the production of ethanol. Ethanol, is also called Ethy alcohol, grain alcohol, or alcohol.
Corn is a high-capacity plant, which undergoes an efficient conversion of radiant energy from the sun into the formation of chemical energy. The energy is found within the plant and its kernels, as cellulose, oil, and starch.
Corn is used as a feed stock for ethanol production, due to its high amounts of carbohydrates, specifically as starch.
Starch is processed to breakdown into simple sugars, which is fed to yeast in order to make alcohol.
Historic Ethanol Usage
The corporation of corn as an ethanol fuel source within the automotive industry, began in 1908. The Ford Motor Company's first car, the Model T, utilized ethanol corn gasoline.
Ethanol History Timeline
- 1826 Samuel Morey developed an engine that ran on ethanol & turpentine.
- 1896 Henry Ford built the quadricycle, which ran on pure ethanol.
- 1908 Ford Motor's first company automobile, Model T, was designed to use corn alcohol.
- 1920 Standard Oil started to incorporate ethanol to gasoline in order to increase octane and reduce engine knocking.
- 1940 First fuel ethanol plant was built by the United States army in Omaha, Nebraska. The purpose was to produce fuel for the army and provide ethanol to blend with fuels.
- 1940-1970 The price of gasoline was very low in the United States, which resulted in no commercial fuel ethanol to be sold to general public.
- 1980's Oxygenates such as Ethyl Tertiary Butl Ether (ETBE) which is made from ethanol and petroleum were added to gasoline.
- 1988 First mandated ethanol oxygenated fuels were in place throughout winter use in Denver, Colorado. This allowed a control over carbon monoxide emissions.
- 1990 Clean Air Act Amendments had mandated the winter use of oxygenated fuels for winter use in 39 areas.
- 1995 Clean Air Act Amendments required full year-round use of oxygenates in 9 areas.
- 1990's to present major United States automobile manufacturers began selling Flexible Fuel Vehicles that run on 85% ethanol.
- 2003 California switched to ethanol in order to create reformulated gasoline.
- 2003 to present majority of U.S. States, followed California and replaced Methyl Tert-Butyl Ether (MTBE) with ethanol.
- 2005 Energy Policy Act of 2005, mandated that gasoline sold in the U.S. contains a minimum value of renewable fuel.
- September 2006 The Renewable Fuel Standard Program (RFS) is signed. This was designed to promote the blending of renewable fuels (ethanol) in motor fuel nationwide.
- December 2007 Energy Independence and Security Act which was signed by our president and congress, required 15 billion gallons of renewable (ethanol) fuel by 2015.
- 2007-2008 There was a surge within individual states mandating the use of 10% ethanol E10 gasoline.
Industrial Ethanol Production
The commercial production of ethanol as a fuel source here in the United States begins with breaking down the starch that is within the corn into simple sugars (glucose). These sugars are fed to yeast in order to induce (fermentation) and the main product produced is ethanol. A byproduct of this process is animal feed. There are two different methods of producing fuel ethanol on an industrial scale. Within the United States these are wet milling and dry grind.
Dry grind consists of over 70% of the ethanol production, due to these type of plants being built at smaller scales at lower investment costs. The overview of this process is processing the whole grain and then separating the residual components at the end of the process.
There are five major steps in the dry-grind production of ethanol.
- Distillation & Recovery
The first step consists of processing corn through a hammer mill that has screens between 3.2 to 4.0 mm. After the initial corn is processed through the mill, it is now corn flour. Water is mixed with this whole corn flour, then a heat-stable enzyme known as, (a-amylase) is added. File:Corn mill.jpg
Liquefaction is the second step, which involves cooking this corn "slurry". The process begins with using jet-cookers that inject steam into the corn flour slurry which allows it to reach temperatures greater than 100°C (212°F). The starch granules within the kernel endosperm are broken apart by the heat and mechanical forces throuhghout the cooking processes. The enzymes are the agent that break down the starch polymer into smaller fragments. This cooked corn mash is cooled to 80-90°C (175-195°F), and additional heat-stable enzyme(a-amylase) is added. This corn slurry continues to liquefy for at least 30 minutes.
This slurry can now be called "corn mash" after the liquefaction process. The mash is cooled to around 30°C (86°F), and a second enzyme called glucoamylase is added to it. Glucoamylase finishes the breakdown of starch into the simple sugar (glucose). The word "saccharification" is used to describe the process that occurs while the corn mash is filling the fermentor in order to prepare for fermentation. saccharification continues onto the fermentation process.
The fermentation step begins with adding yeast that is grown in seed tanks with the corn mash, which begins the process of converting simple sugars into ethanol. The contents within the corn kernel such as the proteins, oil, etc, are unchanged throughout fermentation. This process occurs in batches where a tank is filled, completely ferments, then drained in order to start another batch. After fermentation occurs, the remaining liquid part of the slurry consists of 8-12% ethanol by weight.
Distillation and Recovery
distillation is the process of separating ethanol from water. The separation begins with the knowledge that ethanol has a lower boiling temperature than water. Standard distillation/rectification systems system are able to reach a 92-95% ethanol purity. In order to achieve pure ethanol (>99%) residual water is removed using molecular sieves that adsorb water selectively from an ethanol/water vapor mix. The term "stillage" refers to the residual water and and corn solids that are left after the distillation process. This stillage is seperated using a centrifuge, which seperates the liquid (thin stillage) from the solid pieces of the kernel (distillers' grain). Water can be conserved by recycling some of the thin stillage back to the beginning of this whole dry grind process.
Practical and Efficienct methods of Ethanol Production
upstream processes: Grinding, Liquefaction, and Saccharification
downstream processes: (Distillation and Recovery)
- an efficient dry grind system will continuously employ both up-stream and downstream processes at the same time. Facilities that utilize this method usually have three tanks for fermentation. One is filling, one is fermenting (for 48 hours), and one is being emptied and prepared for the next branch.
- another method of increasing overall efficiency of a dry-grind facility is to capture the Carbon Dioxide that is produced during the fermentation. It can be compressed and sold to soft drink companies for carbonation or frozen to be used as dry-ice.
- Stillage can be evaporated to produce a thick syrup. This syrup can be blended with distillers; grains and dried in order to produce a type of animal feed. This product is called " Distillers' dried grains with solubles" (DDGS). This can be sold to local farmers, helping to close the loop within this bio-ethanol production system. Approximately 17 pounds of DDGS can be made per bushel.
Current dry-grind ethanol plants are able to convert corn grain into ethanol at the rate of around 2.8 gallons per bushel.
Ethanol is considered a renewable energy source. The benifits of utilizing the sun to grow a crop which then can be processed into a transportation fuel outweigh the impacts of turning natural resources into fuel. This alternative fuel conserves petroleum and reduces emissions.
The United states imported around 24% of the nation's consumed petroleum.
Without the blending of ethanol in gasoline, the 24% would have reached 32%.
Transportation accounts for approximately 3/4 of total United States petroleum consumption. The incorporation of ethanol within fuel blends has a significant impact upon emissions released into the atmosphere.
Job Impacts Ethanol production creates jobs within rural areas and promotes employment opportunities where they are needed.
2015 ethanol production led to
- an addition of around 86,000 jobs across the country.
- $44 billion to the GDP
- 24 billion in household income
The incorporation of ethanol in gasoline promotes
- support for the United States economy
- diversity within the United States transportation fleet
- Reduces the impact of international supply disruptions
The carbon dioxide released by a vehicle throughout the combustion of ethanol becomes offset by the carbon dioxide captured when corn is grown to produce the ethanol. Greenhouse gas emissions are reduced by approximately 40% with corn based ethanol produced form dry mills.
Conflicts with producing Ethanol from Corn
Energy Return on Investment (EROI) is dependent upon the resources that were used to grow the corn, ethanol processing, and transporting the fuel.
- Diesel for machinery (Tractors & Combines)
- Natural gas used to nitrogen fertilizer
- Natural gas and electricity at ethanol plant
- Energy used to transport corn ethanol
Conversion of Land to produce Corn
problems associated with conversion of virgin prairies to farmlands
- loss of biodiversity
- Carbon stored as organic matter released into atmosphere
- Causes the contribution of greenhouse gas emissions.
Increasing fertilizer Use
A sudden rise in corn production for the use ethanol, caused a dramatic increase in fertilizer use. This increases the risk of fertilizer runoff into sensitive ecosystems, which can cause significant ecological harm.
Food vs. Energy
Transitioning corn for the use of fuel instead of food causes an increase in the price of corn. The demand for corn increased in order to meet the rising mandates for United States ethanol use in gasoline, which caused a global increase in price of corn. Developing countries who have a high reliance upon corn to meet their daily caloric needs were severely affected.
“Ethanol Benefits and Considerations.” Alternative Fuels Data Center: Ethanol Benefits and Considerations, US Department of Energy, www.afdc.energy.gov/fuels/ethanol_benefits.html.
Mosier, Nathan S., and Klein Lleleji. “How Fuel Ethanol Is Made from Corn.” Purdue University, 3 June 2012, pp. 1–4.
Tverberg, Gail. “What Are the Problems with Using Corn Ethanol for Fuel?” Our Finite World, 10 Jan. 2011, ourfiniteworld.com/2011/01/10/what-are-the-problems-with-using-corn-ethanol-for-fuel/.
Voelcker, John. “EPA Keeps Corn-Based Ethanol Mandate, Rejects Suspension Request.” Green Car Reports, 19 Nov. 2012, www.greencarreports.com/news/1080551_epa-keeps-corn-based-ethanol-mandate-rejects-suspension-request.
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