Saturday, July 22, 2000
Seven steps to ethanol
After harvesting the corn, there are seven steps to making ethanol suitable to use as a gas additive, according to the American Coalition for Ethanol:
1. Milling: The corn is ground into a fine powder called meal.
2. Liquefaction: The meal is mixed with water and alpha-amylase, passing through cookers where the starch is heated to 120-150 degrees Celsius and liquefied and then cooked further at 95 degrees Celsius.
3. Saccharification: The mash from the cookers is cooled and enzymes are added to convert the liquefied starch to fermentable sugars.
4. Fermentation: Yeast is added to ferment the sugars to ethanol and carbon dioxide. Using a continuous process, the fermenting mash is allowed to flow, or cascade, through several fermenters until the mash is fully fermented and then leaves the final tank.
5. Distillation: The fermented mash, now called beer, contains about 10% alcohol, as well as all the non-fermentable solids from the corn and the yeast cells. The mash is pumped to the distillation system where the alcohol will be removed from the solids and the water.
The alcohol leaves the final column at about 96% strength, and the residue mash, called stillage, is transferred from the base of the column to the co-product processing area.
6. Dehydration: The alcohol then passes through a dehydration system where the remaining water will be removed. Most ethanol plants use a molecular sieve to capture the last bit of water in the ethanol. 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.
Byproducts such as carbon dioxide and distillers grains also are processed and sold to provide carbonation for sodas or feed livestock.
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