Corn (Zea Mays) or Maize is a popular crop source for the production of ethanol. Ethanol,which is also called Ethy alcohol, grain alcohol, or alcohol. A class of organic compounds, that are given a generic name of alcohols. Ethyl alcohol is an additive to automotive gasoline which
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.
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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. 1. Milling 2. Liquefaction 3. Saccharification 4. Fermentation 5. Distillation & Recovery
Milling
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, (amylase) is added.
Liquefaction
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.
Saccharification
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.
Fermentation
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 seperating 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.
Up stream 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.
Conclusion
Current dry-grind ethanol plants are able to convert corn grain into ethanol at the rate of around 2.8 gallons per bushel.
See also
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