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The ABC of Ethanol/Gasohol
Home >> Infobank >> Know your vehicle >> The ABC of Ethanol/Gasohol
Introduction

With Govt. of India having recently cleared the decks for phased introduction of Gasohol in various States progressively from 2003 onwards, it may be worthwhile to know more about such a fuel for Automotive consumption.

Gasohol will save the Country Crores of Rupees annually in precious foreign exchange. Besides, it’d develop the present Ethanol Industry in the Country to new heights and all the ‘downstream’ prosperity that goes with it.

What is Ethanol
Ethanol, aka 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 an ‘Alcohol’ - a group of chemical compounds whose molecules contain a hydroxyl group, ‘-OH’, bonded to a carbon atom. The word alcohol derives from Arabic al-kuhul, which denotes a fine powder of antimony produced by distilling antimony and used as an eye makeup. Alcohol originally referred to any fine powder, but medieval alchemists later applied the term to the refined products of distillation, and this led to the current usage.

Ethanol melts at -114.1°C, boils at 78.5°C, and has a density of 0.789 g/ml at 20°C. Its low freezing point has made it useful as the fluid in thermometers for temperatures below -40°C, the freezing point of mercury, and for other low-temperature purposes, such as for antifreeze in automobile radiators.

Ethanol has been made since ancient times by the fermentation of various ‘Sugars’. All beverage grade ethanol and more than half of industrial ethanol is still made by this process. Simple sugars are the raw material. Zymase, an enzyme from yeast, changes the simple sugars into ethanol and carbon dioxide. The fermentation reaction is actually quite complex, and impure cultures of yeast produce varying amounts of other substances, including glycerine and various organic acids.

In the production of beverages, such as whiskey and brandy, the impurities supply the flavor. Starches from potatoes, corn, wheat, and other plants such as Sugarcane/Molasses can also be used in the production of ethanol by fermentation. However, the starches must first be broken down into simple sugars. An enzyme released by germinating barley, diastase, converts starches into sugars. Thus, the germination of barley, called malting, is the first step in brewing beer from starchy plants, such as corn and wheat.

Ethanol produced by fermentation ranges in concentration from a few percent up to about 14 percent. Above about 14 percent, ethanol destroys the
zymase enzyme and fermentation stops. Ethanol is normally concentrated by distillation of aqueous solutions, but the composition of the vapor from aqueous ethanol is 96 percent ethanol and 4 percent water. Therefore, pure ethanol cannot be obtained by distillation.

Commercial Ethanol contains 95 percent pure Ethanol and 5 percent Water by volume. Dehydrating agents can be used to remove the remaining water and produce absolute Ethanol. Much of Ethanol not intended for beverages is now made synthetically, either from acetaldehyde made from acetylene, or from ethylene made from petroleum.

Ethanol can be oxidized to form first acetaldehyde and then acetic acid. It can be dehydrated to form ether. Butadiene, used in making synthetic rubber, may be made from ethanol, as can chloroform and many other organic chemicals.

Content generated by S. K. Gupta. - 11/’02.

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