As aforementioned, ethanol is made by two ways; hydration of ethylene and by the fermentation of sugars or cellulous.
Fermentation
Ethanol is the most common biologically produced alcohol. It is formed from the action of microorganisms and enzymes through the fermentation of sugars or starches, or cellulous, which is a more difficult process than the usage of sugars.
The most widely know process of the formation of ethanol by the means of fermentation begins with carbohydrates; mainly monosaccharides and disaccharides such as glucose, fructose and sucrose. The carbohydrates are converted to cellular energy thereby producing ethanol in the presence of a microbe (usually yeast) and in relatively low heat.
The reaction is catalysed by an enzyme in the yeast called zymase. At temperatures below 25°C, the reaction is slow, whereas at temperatures above 37°C, the enzyme denatures. Therefore, in relation to yield of the ethanol, the reaction is done at a strict temperature of 37°C. The fermentation is carried out non-aseptically in the absence of air for about 1-3 days where it would be distilled.
Another method of forming ethanol from fermentation is by using cellulosic materials. There is a higher yield of ethanol from this process in comparison to the fermentation of sugars
Lingocellulosic materials such as hardwood and softwood residue is used - the process consist of hydrolysis on pretreated cellulosic materials, using enzymes to break complex cellulose into simple sugars such as glucose. This is followed by the fermentation of the sugars and finally distilled.
Cellulosic material can also be fermentated by gasification. This transforms the raw material into gaseous carbon dioxide and carbon dioxide. These gases can be converted to ethanol by the fermentation or chemical cataylsis.
Hydration of Ethylene
Ethanol for use as an industrial feedstock is made by the hydration of ethylene. Excess water is reacted with the ethylene in the presence of a catalyst (most commonly phosphoric acid) and under high pressure and a temperature of 300°C.
(g) + (g) → CH3CH2OH(l).