Ethanol

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By Linda | April 6, 2008

With record oil prices once again topping the headlines, today’s “Science Word of the Week” is “Ethanol”.

Ethanol is a colorless volatile flammable liquid. It is a form of alcohol, C2H5OH, found in alcoholic beverages and also used as an additive in gasoline to produce gasohol. Ethanol is used as an oxygenate in reformulated gasoline. It is also used to enhance the performance of octane in fuels.

The steps for converting corn to ethanol for use as a fuel are:

1. Milling: The corn will first pass through hammer mills, which grind it into a fine powder called meal.

2. Liquefaction: The meal will then be mixed with water and alpha-amylase, and will pass through cookers where the starch is liquefied.

3. Saccharification: The mash from the cookers will then be cooled and the secondary enzyme (gluco-amylase) will be added to convert the liquefied starch to fermentable sugars (dextrose).

4. Fermentation: Yeast will then be added to the mash to ferment the sugars to ethanol and carbon dioxide.

5. Distillation: The fermented mash, now called “beer,” will contain about 10% alcohol, as well as all the non-fermentable solids from the corn and the yeast cells. Here, the ethanol is separated from the solids known as “stillage.”

6. Dehydration: The ethanol then enters a dehydration system where the remaining water will be removed. The alcohol product at this stage is called anhydrous (pure, without water) ethanol and is approximately 200 proof.

7. Denaturing: Ethanol that will be used for fuel is then denatured with a small amount (2-5%) of some product, like gasoline, to make it unfit for human consumption.

8. Co-Products: There are two main co-products created in the production of ethanol: carbon dioxide and distillers grain dry and wet. Carbon dioxide is given off in great quantities during fermentation and many ethanol plants collect that carbon dioxide, clean it of any residual alcohol, compress it and sell it for use to carbonate beverages or in the flash freezing of meat. Distillers grains, wet and dried, are high in protein and other nutrients and are often used as livestock feed.