In this article we will discuss about the production of ethyl alcohol.
Ethyl alcohol is the most common solvent and raw material. It is next to water and is used in laboratory and chemical industry. Much of this alcohol is obtained synthetically from ethylene. However, its production from microbial fermentation using variety of cheap sugary substrates is still commercially important.
It is imperative that the microorganisms used must have a high tolerance for alcohol, must grow vigorously and produce a large quantity of alcohol. Yeasts, particularly Saccharomyces cerevisiae, represent the best known microorganisms used in the production of ethyl alcohol.
Some of the inexpensive substrates used in alcohol industry are molasses from cane sugar or waste sulphite liquor from paper industries. Starch yielding grams (corn), potatoes, grapes may also be used as substrate if their prices permit. Some countries used sugar-beet for the purpose.
Reaction:
The chemical reaction that results in the microbial fermentation of carbohydrate into alcohol can be represented as follows:
1. Commercial Production using Molasses as Raw Material:
Molasses contain about 50% fermentable carbohydrates (sugars). Big deep tanks of steel or stainless steel are used as containers in the industrial production method (Fig. 40.1).
Molasses is diluted to a suitable sugar concentration (15-16%); a small quantity of nitrogen source (e.g., ammonium phosphate, urea, ammonium sulphate) and sulphuric acid (H2SO4) is added in it. pH of this medium is maintained at about 5.0 and an actively growing Saccharomyces cerevisiae culture is added in it.
The fermentation starts and is allowed to proceeding for about 24-40 hours at about 25-30°C temperature. The fermented medium is then distilled and passes through rectifying columns to obtain ethyl alcohol. The yield of ethyl alcohol ranges about 50% of the fermentable sugar concentration present in the medium.
The large amount of CO2 which is produced during the fermentation process as a result of decarboxylation is recovered and compressed to its solid state. The yeast recovered is usually used as an animal feed.
2. Commercial Production Using Starch as Raw Material:
When starches such as corn are used as the raw material they have first to be hydrolysed to release simple fermentable sugars. The hydrolysis can be accomplished with enzymes from barley malt or moulds (e.g., Aspergillus oryzae) or by heat-treatment of acidified material. After the simple fermentable sugars are obtained, the fermentation process proceeds similarly to that of molasses.
