Making Ethanol

How ethanol is made: from the corn plant to the production plant.

Most U.S. ethanol is made from corn, but the production process is versatile. It works with most sugar-containing plant materials, such as sorghum, wheat, barley and potatoes! In fact, ethanol producers in Brazil - the world's largest maker of ethanol - use sugar cane to start the process.

In the United States, there are more than 95 ethanol production facilities, with 16 more currently under construction - many of which are owned by farmer investors. In 2005, these facilities produced nearly 4.3 billion gallons of ethanol - enough to enrich 30 percent of all gasoline sold in the United States.

So how is a bushel of corn (or other feedstock) transformed into more than two gallons of high-performance fuel? It's an eight-step process that takes several days. Read on for the inside story.

1. Milling around
   The corn is ground into small particles. This exposes the cornstarch, which will be used for the fermentation process. The cornstarch is removed and milled into a fine powder. The remaining grain material - protein, fiber, vitamins and minerals - is used for livestock feed.
     
2. We're cookin' now
   The cornstarch powder is mixed with water and alpha-amylase, an enzyme that helps break the starch into smaller particles. The resulting mash is cooked at 120 to 150 degrees to liquefy the starch and reduce bacteria levels, and then heated to 225 degrees to help break the starch down further.
     
3. Sweet!
   The mash is removed from the cookers and cooled. Then a second enzyme, glucoamylase, is added to help convert the liquid starch into a sugar (dextrose) that can be fermented.
     
4. Destination: fermentation
   The mash is mixed with yeast, which changes the sugar to ethanol and carbon dioxide. It takes about 48 hours for the mash to ferment.
     
5. In distill of the night...
   The fermented mash contains about 10 percent ethanol. The rest of the mixture is water and corn/yeast solids that couldn't be fermented. To separate the ethanol, the mixture is heated once again - this time to a temperature at which ethanol vaporizes, but the remaining materials do not. The ethanol vapor is collected and cooled, where it condenses to its liquid form.
     
6. Dehydration (it's a good thing)
   To purify the ethanol and remove any remaining water, it's passed through a dehydration system, creating anhydrous ethanol (anhydrous means "without water"). After this step, the ethanol is approximately 200 proof ... which explains the need for step seven.
    
7. Potent, but not potable
   To make the ethanol unfit for human consumption - a requirement for all fuel-grade ethanol - a small amount of gasoline is added (2 percent to 5 percent).
    
8. On the side
   The leftovers, or co-products, of the process - distiller's grain and carbon dioxide - are saved. Distiller's grain is a highly nutritious livestock feed, and carbon dioxide is collected, purified, compressed, and sold for use by the carbonated beverage and dry-ice industries.

Source: http://www.drivingethanol.org/ethanol_facts/producing_ethanol.aspx

  

Take a video tour (Windows Media Player required) of an Ethanol Plant and learn about the production process from start to finish! (Courtesy of Midwest Grain Processors.)

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