Ethanol Production

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BOTANY: SEM-VI, PAPER- DSE-3T: INDUSTRIAL AND ENVIRONMENTAL MICROBIOLOGY, UNIT 3: MICROBIAL PRODUCTION OF INDUSTRIAL PRODUCTS

COMPILED AND CIRCULATED BY DR. PRITHWI GHOSH, ASSISTANT PROFESSOR, DEPARTMENT OF BOTANY, NARAJOLE RAJ COLLEGE

Ethanol Production

Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic chemical compound. It is a simple alcohol with the chemical formula C2H6O.and is often abbreviated as EtOH. Ethanol is a volatile, flammable, colorless liquid with a slight characteristic odor. It is a psychoactive drug, recreational drug, and the active ingredient in alcoholic drinks. Ethanol is naturally produced by the fermentation of sugars by yeasts or via petrochemical processes such as ethylene hydration. It has medical applications as an antiseptic and disinfectant. It is used as a chemical solvent and in the synthesis of organic compounds. Ethanol is also a fuel source.

Both yeasts (Saccharomyces cerevisiae, S. uvarum S. carlsbergensis, Candida brassicae, C. utilis, Kluyveromyces fragilis, K. lactis) and bacteria (Zymomonas mobilis) have been employed for ethanol

production in industries.

The commercial production is carried out with Saccharomyces cerevisiae.

It is noteworthy that the ethanol at high concentration inhibits the yeast. Hence, the concentration of ethanol reduces the yeast growth rate which affect the biosynthesis of ethanol. It can produce about 10-12 % ethanol but the demerit of yeast is that it has limitation of converting whole biomass derived by their ability to convert xylulose into ethanol. The Zymomonas has a merit over yeast that it has osmotic tolerance to higher sugar concentration. It is relatively having high tolerance to ethanol and have more specific growth rate.

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Preparation of Medium:

Three types of substrates are used for ethanol production:

(a) Starch containing substrate,

(b) Juice from sugarcane or molasses or sugar beet,

(c) Waste products from wood or processed wood. Production of ethanol from whey is not viable.

If yeast strains are to be used, the starch must be hydrolyzed as yeast does not contain amylases. After hydrolysis, it is supplemented with celluloses of microbial origin so as to obtain reducing sugars. About 1 ton of starch required 1 litre of amylases and 3.5 litre of glucoamylases. On the other hand, if molasses are used for ethanol production, the bagasse can also give ethanol after fermentation. Several other non- conventional sources of energy such as aquatic plant biomass, wood after hydrolysis with celluloses gives ethanol.

There are following steps in ethanol production:

• Milling

• Liquefaction

• Saccharification

• Fermentation

• Distillation

• Dehydration Milling:

• The feedstock is passed through a hammer mill which grinds it into a fine powder called a meal.

Liquefaction:

• The meal is mixed with water and alpha-amylase.

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• Then passed through cookers where the starch is liquified and heat is applied here to enable liquefaction.

• Cookers with the high-temperature stage (120-150˚C) and lower temperature holding period (95˚C) are used.

• High temperatures reduce bacteria levels in the mash.

Saccharification:

• The mash from the cookers is cooled.

• And secondary enzyme glucoamylase is added.

• This converts the liquified starch into the fermentable sugars.

Fermentation:

• Yeast is added to ferment the sugars to ethanol and carbon dioxide.

• In a continuous process, the fermenting mash can flow through several fermenters until it is fully fermented and leaves the final tank.

• In a batch process, the mash stays in one fermenter for about 48 hours before distillation starts.

Ethanol is mainly produced by continuous fermentation. Hence, large fermenters are used for continuous manufacturing of ethanol. The process varies from one country to another. The fermentation conditions are almost similar (pH 5, temperature 35°C) but the cultures and culture conditions are different. The fermentation is normally carried out for several days but within 12h starts production. After the fermentation is over, the cells are separated to get biomass of yeast cells which are used as single cell protein (SCP) for animal’s feed.

Extraction of the final product:

Distillation:

• Mash is pumped to continuous flow.

• Multicolumn distillation system where the alcohol is removed from solid and water.

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• The alcohol leaves the top of the final column at about 96% strength.

• The residue mash is called stillage which is transferred from the base of the column to the co-product processing area.

Dehydration:

• The alcohol from the top of the column is passed through a dehydration system where the remaining water will be removed.

• Most ethanol plants use a molecular sieve to capture the last bit of water in the ethanol.

• The alcohol product at this stage is called anhydrous alcohol.

By-Products

Three byproducts generated

1. Carbon dioxide- used for production of dry ice and pure form used for preparation of soft drinks.

2. Yeast biomass- used for animal fodder because it contains high protein, vitamins etc.

3. Distillery effluents- used as a fertilizer and animal feed.

Application

• In many medicines and drugs.

• As a disinfectant and in tinctures.

• Used as a biofuel (99.2%).

• Medically ethanol is soporific.

• Used as antiseptic.

• Fluid in many alcohol thermometer.

• 92.4% ethanol is used as solvent in cosmetics pharmaceuticals and chemical industry Byproduct

• DDGS (distillers dried grain with soluble)

• Co₂– used for the production of dry ice and preparation of soft drinks Yeast biomass- animal fodder (contains proteins &vit)

References

• www.biologydiscussion.com

• www.slideshare.com

• www.onlinebiologynotes.com

[The information, including the figures, will be used solely for academic purpose.]