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. |
