Bioethanol

Ethanol is a flammable colorless liquid. When used as an alternative fuel, ethanol is referred to simply as Bioethanol. Bioethanol is frequently used as motor fuel or as an additive in gasoline and is an option for more "renewable" energy. For information on the basic chemical properties of this substance, see ethanol.

Figure 1: Bioethanol manufacturing plant.

Production

Ethanol is either produced from petroleum or biomass. It is the ethanol produced from biomass that is most often referred to as bioethanol. Bioethanol is chemically identical to petroleum derived ethanol. Usual feedstocks of bioethanol include corn, switchgrass, sugar cane, algae, or other biomass. The feedstocks undergo fermentation, during which certain species of yeast digest the sugar contained in the feedstocks. The process releases bioethanol and carbon dioxide. Ethanol is mainly produced in Brazil, the United States, Europe, and South Africa.

Uses

Figure 2: A bioethanol fueled city bus.

Besides alcoholic beverage production, ethanol is also used as an alternative fuel to gasoline for internal combustion engines. It can be mixed with gasoline to any percentage, and all existing gasoline engines on automobiles can operate with blends of up to 10% ethanol with gasoline.

However, ethanol has a lower energy density than that of gasoline, meaning more ethanol - in terms of volume and mass - needs to be combusted to produce the same amount of energy. In fact, energy per unit volume of ethanol is 34% lower than that of gasoline, therefore 1.5 gallons of ethanol contains approximately the same amount of energy as one gallon of gasoline does.

An additional advantage of ethanol is that it has a higher octane rating than gasoline, allowing engine designs with higher compression ratios, meaning ethanol driven engines can be designed to have higher thermal efficiency. Although the energy contained per gallon of ethanol is less than gasoline, as the energy within the fuels is converted to the mechanical movements of the vehicle, the ethanol engine will waste less energy as compared to that of gasoline. An ethanol-only engine can be designed for better theoretical power output and higher thermal efficiency, meaning an ethanol powered car will have better performance and waste less energy. Also, if bioethanol is used, the carbon dioxide released when ethanol is burned is balanced by the carbon dioxide captured when the crops are grown to make ethanol. This differs from petroleum, which is made from plants that grew millions of years ago. On a life cycle analysis basis, corn-based bioethanol production and use reduces greenhouse gas emissions (GHGs) by up to 52% compared to gasoline production and use. Bioethanol use could reduce GHGs by as much as 86%.