What is Bioethanol?

Ethanol is a two-carbon hydrocarbon with a hydroxyl group. Ethanol, itself, is a clear, flammable, colorless liquid that is miscible with water, as its hydrophilic hydroxyl group is capable of hydrogen-bonding with water molecules. Bioethanol refers to ethanol that is produced from biomass such as corn or sugar cane. It can be procured from biomass via fermentation of sugars and starches that result from the processing of harvested crops.

Ethanol is used industrially, and in other manners, as a mixture of 95% ethanol and 5% water because this is the composition that results from total distillation. Although ethanol’s boiling point (78.3 degrees centigrade) falls well below water’s (100 degrees centigrade), ethanol can not be further purified beyond this mixture (called an azeotropic mixture) by distillation because the vapor contains the exact same alcohol/water composition as the liquid at this point.

What are some uses of bioethanol?

1. Hydrous ethanol (95% ethanol, 5% water), described above, can be used as a full substitute for gasoline in automobile engines, but this fuel requires special engines that are modified for such a purpose. Standard spark-ignition gasoline cars can not utilize this technology.

2. Anhydrous ethanol (at least 99% ethanol, at most 1% water) can be used as a partial gasoline substitute, blended with conventional fuel between ratios of 5% and 85% (E85) ethanol. Cars with standard spark-ignition engines can utilize a 10% ethanol substitute (E10) without modification. Higher blends require modified engines and vehicles containing these engines are known as “flexible fuel” vehicles (FFVs).

3. Bioethanol can also be used to manufacture ethyl t-butyl ether (ETBE), which is a fuel additive for conventional petrol formulated to reduce engine knocking, increase octane rating, and lower vehicle emissions.

Ethanol, itself, is useful as an oxygenate additive to gasoline, which reduces engine knocking and improves octane rating considerably (see comparisons below). Because of this more refined combustion, ethanol reduces harmful emissions like carbon monoxide. It is increasingly replacing methyl t-butyl ether (MTBE) as the most popular oxygenate additive, as it became known that MTBE is a dangerous groundwater and soil contaminant.

What are the advantages of bioethanol?

Like other biomass fuels, bioethanol is an advantageous replacement for fossil fuels because it is a renewable agricultural source and it does not add net carbon dioxide—a greenhouse gas—to the atmosphere. The carbon dioxide released by the combustion of ethanol is absorbed by agriculture, which will eventually be converted to ethanol, and thus a carbon dioxide balance is maintained in the atmosphere.

As use of ethanol fuel increases, agricultural markets will expand. Since bioethanol can be procured from nearly any type of crop—corn and sugar or even trees and straw—it is an available, sustainable fuel for even the least industrialized nations. For ethanol production from cellulosic materials, see Major Issue: Cellulosic Ethanol. In addition, energy security will increase in many countries, as governments will become less reliant on foreign petroleum exports.

Ethanol, itself, has a much higher octane rating than gasoline, and thus improves the compression ratio of an internal combustion engine, allowing for increased thermal efficiency. Cropland, which can be converted to ethanol fuel, is far more abundant and widespread than oil fields or wells, and thus many nations have far greater access to ethanol. For this reason, ethanol production has grown at an accelerated rate, and is expected to do so in the coming years as well. The United States, behind Brazil, is the world’s second leading bioethanol producer. Currently, the U.S. is making over four billion gallons of ethanol annually.

What are the disadvantages of bioethanol?

Like any fuel, bioethanol too has its problems. Many of them are temporary, however, simply requiring conversion of infrastructure of vehicles, fuel storage, and transportation from gasoline to ethanol. One example is the required change to flexible-fuel vehicles (FFVs), which are able to utilize both gasoline and ethanol fuels of any concentration, as mentioned above. Today’s automobile engines can only tolerate ethanol mixtures up to 10%, but FFVs can run on E85 or E100 fuels. Some FFVs are already in circulation, and are often marked like the one pictured here with the words, “Flex Fuel.”

As ethanol is highly miscible with water, contamination of ethanol-blended gasoline with moisture can cause phase separation, and therefore destruction of the fuel. Transport of ethanol with gasoline in underground pipes, therefore, could be problematic. Some scientists have recommended avoiding this problem by transporting ethanol and gasoline separately and mixing the two at the fueling station, but this process is costly both energetically and economically.

Perhaps one of the most feared disadvantages of bioethanol is the “food vs. fuel” dilemma, which is discussed in detail in this website’s “Biodiesel” section (see Major Challenge: Food or Fuel?). Should bioethanol become a leading fuel source throughout the world, crops would be held at a premium both for food and fuel, requiring rationing of one or the other or both.



Navigating the Bioethanol Page:


Background:……………Chemistry………………………..Sources………………..Processing


Major Issues:………….Cellulosic Ethanol……………Biobutanol……………Feasibility Disputes

Sources

American Coalition for Ethanol. “All about Ethanol.” www.ethanol.org.

Bradley, Jack. “Making fuel in your backyard.” Wenatchee, WA: Biomass Resources, 1979.

Paisley, Mark A. “Biomass Energy.” Kirk‑Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, 2003.

Pereira, A. Ethanol, Employment and Development: Lessons from Brazil. Geneva: International Labour Organisation, 1996, p. 13-23.

Spiro, Thomas G. and William M. Stigliani. Chemistry of the Environment, 2nd ed. Upper Saddle River, NJ: Prentice Hall, 2003, p. 88-90.

Turon, Martin. Ethanol as Fuel: An Environmental and Economic Analysis. Turon Technologies, Inc., 2000.

United States Department of Energy: Energy Efficiency and Renewable Energy. Alternative Fuels Data Center, “Ethanol.” www.eere.energy.gov.

Wikipedia, the free encyclopedia. “Ethanol Fuel.” Last modified 8 January 2007.