WHAT IS ETHANOL?

Ethanol (ethyl alcohol, grain alcohol, EtOH) is a clear, colorless liquid with a characteristic, agreeable odor. In dilute aqueous solution, it has a somewhat sweet flavor, but in more concentrated solutions it has a burning taste. Ethanol (CH3CH2OH) is a group of chemical compounds whose molecules contain a hydroxyl group, -OH, bonded to a carbon atom. Ethanol made from cellulosic biomass materials instead of traditional feedstocks (starch crops) is called bioethanol.

The Clean Air Act Amendments of 1990 mandated the sale of oxygenated fuels in areas with unhealthy levels of carbon monoxide. Since that time, there has been strong demand for ethanol as an oxygenate blended with gasoline. In the United States each year, more than 1.5 billion gallons are added to gasoline to increase octane and improve the emissions quality of gasoline. In some areas, ethanol is blended with gasoline to form an E10 blend (10% ethanol and 90% gasoline), but it can be used in higher concentrations such as E85 or in its pure form. All automobile manufacturers that do business in the United States approve the use of certain ethanol/gasoline blends. Fuel ethanol blends are successfully used in all types of vehicles and engines that require gasoline. Approval of ethanol blends is found in the owners' manuals under references to refueling or gasoline.

Chemical properties: Ethanol is ethane with a hydrogen molecule replaced by a hydroxyl radical. See the fuel properties table (PDF 116 KB) for more information.

How is ethanol made?

The eight steps in the ethanol production process follow:

Milling: The feedstock passes through hammer mills, which grind it into a fine meal.

Liquefaction: The meal is mixed with water and alpha-amylase, and passes through cookers with a high temperature stage (120o-150oC) and a lower temperature holding period (95oC), where the starch is liquefied. Heat is appied to enable liquefaction. The high temperatures reduce bacteria levels in the mash.

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

Fermentation: Yeast is added to the mash to ferment the sugars to ethanol and carbon dioxide (CO2). 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. In a batch fermentation process, the mash stays in one fermenter for about 48 hours before the distillation process is started.

Distillation: The fermented mash, now called "beer," contains about 10% alcohol, as well as all the nonfermentable solids from the corn and the yeast cells. The mash is pumped to the continuous flow, multicolumn distillation system where the alcohol is removed from the solids and the water. The alcohol leaves the top of the final column at about 96% strength, and the residue mash, called stillage, is transferred from the base of the column to the coproduct processing area.

Dehydration: The alcohol from the top of the column passes through a dehydration system where the remaining water is 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.

Denaturing: Fuel ethanol is denatured with a small amount (2%-5%) of some product such as gasoline, to make it unfit for human consumption.

Coproducts: Two main coproducts--CO2 and distillers grain--are created during ethanol production. CO2 is given off in great quantities during fermentation. Many ethanol plants collect the CO2, clean it of any residual alcohol, compress it, and sell it for use in carbonate beverages or to flash freeze meat. Wet and dried distillers grains are high in protein and other nutrients and are highly valued livestock feed ingredients. Some ethanol plants also create a "syrup" that can be sold in addition to, or combined with, the distillers grain. Ethanol production is a no-waste process that adds value to the feedstock by converting it into more valuable products. Ethanol is also made from a wet-milling process. Many larger ethanol producers use this process, which also yields products such as high-fructose corn sweetner.

What is the market for ethanol? Ethanol is already penetrating the transportation market as gasohol. Although an exact figure is not available, there are many gasohol outlets. However, ethanol used in gasohol is not an alternative fuel as defined by EPAct--it is a replacement fuel. Few outlets for high-level ethanol blends are available, but the major automobile manufacturers have models that can operate on blends as high as 85%.

To learn more about ethanol vehicles and to see which ethanol vehicles are available for sale or lease, visit the AFDC Ethanol Vehicle Page.

What are the benefits of ethanol?

It reduces our dependence on foreign oil. It reduces air pollution. It is a renewable fuel. For more detailed information on ethanol benefits, visit the American Coalition for Ethanol Web Page. How can I learn more about ethanol?

For more information about ethanol, visit the following Web sites:

Ethanol Information Centre's FAQs Page The California Energy Commission's Ethanol Report You may also call the National Alternative Fuels Hotline (800) 423-1DOE. Research and development

DOE's program dedicated to ethanol research and development--the DOE Biofuels Program

Other resources

Documents

http://www.ethanol.org/ethanol_info.html