This article is the fourth in a series examining alternative fuels production and source materials. Previously we have taken a look at biodiesel, natural gas, and propane. In the next couple of months we will cover hydrogen, and electricity, as a vehicle fuel. This month, our focus is on ethanol.
What is ethanol?
Ethanol is an alternative fuel made from corn, sugarcane, wheat, and other agricultural products, and is produced by the fermentation of carbohydrates such as sugar, starch, and cellulose.
All plants contain sugars that can be fermented to make ethanol in a process called biochemical conversion. Plant material can also be converted to ethanol using heat and chemicals in a process called thermochemical conversion.
Sugarcane is one of the most promising agricultural products to convert into ethanol due to its high sugar content. During the fermentation process, these sugars are turned into alcohol, or ethanol. Sugar beets are also very high in sugar content and are second to sugarcane in their ability to produce ethanol. In the U.S., sugarcane is planted and harvested in Hawaii, Florida, Louisiana, and Texas. Grains like wheat, oats, rye, rice, and barley also may be used to produce ethanol.
Corn, one of America’s most widely produced agricultural products, is a carbohydratemeaning that it is especially high in sugarsmaking it an ideal feedstock for producing ethanol. In fact, corn is the feedstock used for more than 90% of the current U.S. ethanol production.
Ethanol plants commonly produce ethanol through a process called dry milling. Credit: NAFTC.
Ethanol can also be produced by breaking down cellulose (sugar) in woody fibers. This type of ethanol is called cellulosic ethanol. Plants and trees contain cellulose and hemicelluloses, and these polymers form the structures of plants, including their stalks, leaves, trunks, branches, and husks.
Dry milling is the most common ethanol production method in the U.S. This process involves grinding up corn or other grains into a flour or meal, and then mixing it with water to form what is known as mash.
Once the mash is heated, enzymes are added to break down the starch, producing a simple sugar. Yeast is added during the fermentation process, causing the simple sugars to convert into ethanol and carbon dioxide.
Upon fermentation, the raw material is distilled to separate the ethanol from the remainder of the mash, which is now called silage. Finally, denaturant is added to ensure that the product is not mistakenly used for human consumption.
This article is based on the Clean Cities Learning Program Petroleum Reduction Technologies curriculum. For more information, visit the Clean Cities Learning Program or contact the NAFTC.