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Know How Bioethanol is Produced?

Poushali Ganguly Mar 5, 2020
With the natural stock of petroleum depleting fast, finding suitable alternative fuels has become the need of the hour. Among the many possible options out there, one is bioethanol, which can be produced from biological matter. We will go through some of the methods used in making this substitute fuel.
In the production of bioethanol, there are two key reactions that are involved. One is hydrolysis and the other is fermentation. The traditional way of producing bioethanol involves mixing together sugar, water, and yeast bacteria, which are then allowed to ferment in a warm environment.
Gradually, the mixture becomes a liquid that has approximately fifteen percent alcohol content. As the alcohol percentage in the mixture increases, the yeast is eventually killed by it, thus ending the fermentation process altogether. Then the liquid mash that is created is distilled and purified to get approximately 99.5% pure bioethanol.
Thus, the process of fermentation is a series of chemical reactions, wherein, the simple sugars are converted into ethanol. Yeast or bacteria, which feed on these sugars, cause the reaction to take place, and thus fermentation occurs. Ethanol and carbon dioxide are produced as metabolic byproducts when the yeast consumes the sugar.
There is a simple formula that represents this process of fermentation:

C6H12O6 (glucose) -> 2 CH3CH2OH (ethanol)+ 2 CO2 (carbon dioxide)
Using this kind of production process, bioethanol can be derived from a variety of sugar and starch-rich crops, which include grain, corn, sugarcane, and sugar beet.
This traditional process of production of this substitute fuel is well-known and easy, as it comprises only the fermentation of the sugar, which is similar to the process used for obtaining beverages like whiskey or vodka.
There is another hypothetical method of making bioethanol, wherein, it could be derived from materials that have lignocellulose, which primarily is a strengthening substance found in the tissues of woody plant matter, such as straw, cornstalks, wood chippings, and other organic materials that are often considered waste.
Currently, there are certain biological barriers in bringing this method into practice. As and when this method will become practically possible to employ, the cost of production of bioethanol would significantly reduce, as the raw materials needed would be more easily available all over the world.
Also, since this process would allow ethanol to be produced from a more diverse range of organic matter, it will be more productive as compared to the traditional method. 
It is estimated that through this method, the output of bioethanol would be doubled, that too without straining the food chain. The output of this new process would also be far more energy efficient, and would have lower carbon dioxide emissions as well.

Production Process

1) Firstly, the biomass first goes through a step that reduces the size of the material, so that it is easier to handle, and to make the production process more efficient. It is much like the grinding process that agricultural residues go through, so that the particles have a near uniform size.
2) The next step is to treat the biomass, in which the hemicellulose fraction of it is broken down into simple sugars. It takes place with the help of a simple chemical reaction called hydrolysis, which occurs when dilute sulfuric acid is mixed with the biomass feedstock.
In this reaction, the complex chains of sugars in the hemicellulose are broken down, releasing simple sugars. The complex hemicellulose sugars are transformed into a mix of soluble five-carbon sugars - xylose and arabinose, and soluble six-carbon sugars - mannose and galactose. A small portion of the cellulose is also transformed into glucose.
There are a few enzymes that are used like the cellulase enzymes, which hydrolyze the cellulose part of the biomass. These enzymes are either produced in the last mentioned step, or are to be bought and added.
3) After the hydrolysis of cellulose, the glucose and pentose are fermented, which gives 'ethanol broth' as an output. A final step of dehydration removes the excess water from the ethanol. This step is known as ethanol recovery. Then, the other by-products, including lignin, are used to produce the electricity that is required for the production of ethanol.

Ethanol biorefinery

Presently, this whole process is quite expensive to implement. Therefore, scientists are working hard to find ways to reduce the cost, so that the production becomes cost-effective, which would lead to a considerable increase in the usage of biofuel.