Ethanol, also known as ethyl alcohol or grain alcohol, is a colorless liquid that is produced by the fermentation and distillation of starch crops, such as corn, barley, that have been converted into simple sugars. Its chemical formula is C2H5OH. Ethanol can also be produced from cellulosic biomass such as trees and grasses and is called bioethanol. It is most commonly used to increase octane and improve the emissions quality of gasoline and is also used as an alternative fuel.
Ethanol can be blended with gasoline to create E85, a blend of 85% ethanol and 15% gasoline. E85 and blends with even higher concentrations of ethanol, E95, for example, qualify in the US as alternative fuels under the Energy Policy Act of 1992 (EPAct). Vehicles that run on E85 are called flexible fuel vehicles (FFVs) and are offered by several vehicle manufacturers.
How is ethanol made?Ethanol can be produced from any biological feedstocks that contain appreciable amounts of sugar or materials that can be converted into sugar such as starch or cellulose. Sugar beets and sugar cane are examples of feedstocks that contain sugar. Corn contains starch that can relatively easily be converted into sugar. A significant percentage of trees and grasses are made up of cellulose, which can also be converted to sugar, although with more difficulty than required to convert starch.
The ethanol production process starts by grinding up the feedstock so it is more easily and quickly processed in the following steps. Once ground up, the sugar is either dissolved out of the material or the starch or cellulose is converted into sugar. The sugar is then fed to microbes that use it for food, producing ethanol and carbon dioxide in the process. A final step purifies the ethanol to the desired concentration.
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 sweetener.
Net energy balance of ethanolSince President Bush announced the Advanced Energy Initiative, there has been an increased interest in ethanol as a fuel. Cellulosic ethanol can be produced from fast growing trees, corn stover, grain straw, switchgrass, forest products, waste, and construction waste and may yield a higher energy balance than ethanol made from corn.
The production of ethanol is energy efficient as it yields almost 25 percent more energy than is used in growing the corn, harvesting it, and distilling it into ethanol. The most recent findings show that corn ethanol fuel is energy efficient and yields an energy output:input ratio of 1.6.
Early ethanol plants were energy intensive, raising concerns as to whether the transportation fuel being produced was worth the energy going into making it. But the efficiency of corn ethanol production has increased over the last ten years and technical advancements have improved the net energy value of corn ethanol. Today, producing ethanol from corn using our domestic supplies of coal and natural gas achieves a net gain in the form of energy and helps displace the need for foreign oil.
One of the biggest critics of fuel ethanol is David Pimentel, Cornell University. He asserts that it takes about 70% more energy to grow corn and make ethanol from it than what goes into the ethanol. Among other things, however, his analysis is based on old data and does not give any credit for the energy value of the animal feed coproduct of making ethanol.
Related categories• FUELS
Home • About • Copyright © The Worlds of David Darling • Encyclopedia of Science • Contact