Clean Tech 101

What is Bioethanol?

Bioethanol can be blended with petroleum to produce a much more efficient fuel
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Biofuels are liquid or gaseous fuels that are produced from biodegradable fractions of products, remains from agricultural production and forestry, as well as biodegradable fractions of industrial and municipal wastes.

However, ethanol produced from renewable energy sources is one of the most promising biofuels for the future. Although bioethanol fuels can be manufactured using the chemical reaction between ethylene and stream, it is mainly produced through fermentation of sugars derived from crops containing starch, such as corn, wheat, sugar cane, sorghum plants, etc.

It is currently used in the fuel industry as an additive for petrol. It is a high octane fuel and has replaced lead as an octane enhancer in petrol. Blending ethanol with petrol oxygenates the fuel mixture so that it burns completely and reduces harmful emissions. The most common blend is 90% petrol and 10% ethanol.

Bioethanol is entirely comprised of biological products, and hence the combustion of bioethanol results in cleaner emissions (carbon dioxide, steam and heat). Carbon dioxide is absorbed by plants and processed via photosynthesis to help the plant grow. This cycle of creation and energy combustion means bioethanol could potentially be a carbon neutral fuel source.

Bioethanol Production

Biomass wastes consist of a complex mixture of carbohydrate polymers such as cellulose, hemi cellulose and lignin. Biomass is pre-treated with acids or allowed to react with enzymes to reduce the size of the feedstock and produce sugars.

The carbohydrate polymers are broken down with the help of enzymes or dilute acids into sucrose sugar and then fermented into bioethanol. However, the lignin present in the biomass is used as a fuel for boilers in which bioethanol is produced. Enzymatic hydrolysis, concentrated acid hydrolysis and dilute acid hydrolysis are the three basic methods for extracting sugar from biomass.

Biomass can be used to produce large amounts of bioethanol
Image credit: KPG Payless2 / Shutterstock.com

On the other hand, corn can be processed into ethanol by either dry milling or wet milling. In the dry milling process, the corn kernel is cleaned and broken down into fine particles through hammer milling. This process creates a powder with a course flour-type consistency. The wet milling process involves soaking corn kernel in warm water to break down its proteins and release starch.

Once the biomass or corn is broken down into sugar via the hydrolysis process, the sugar solution is ready to be fermented into ethanol. The addition of yeast to the solution followed by rapid heating converts the sucrose sugars into fructose and glucose with the help of invertase present in the yeast.

These sugars further react with another enzyme, zymase, contained in the yeast to yield ethanol and carbon dioxide. The fermentation process is carried out at temperatures between 250 and 300°C. The ethanol thus produced undergoes the fractional distillation process to remove excess water produced during the fermentation process.

Biofuels as Renewable Energy: Ethanol From Corn
Video credit: mnagriculture / YouTube

Benefits of Bioethanol

Bioethanol has a number of benefits when compared to conventional fuels. Firstly, it is produced from a renewable resource (such as crops). There is therefore little/no net carbon dioxide added to the atmosphere, making bioethanol an environmentally beneficial energy source.

The road transport network contributes a great deal to the release of greenhouse gas emissions into the atmosphere, and with the use of bioethanol, emission rates can be drastically reduced. It is also biodegradable, and less toxic than fossil fuels.

In addition, blending bioethanol with petrol compensates for the diminishing oil supplies across the globe thereby ensuring higher fuel security and avoiding foreign reliance for fuel supply between countries. The rural community will also benefit from the increased demand to grow the necessary crops required for producing bioethanol.

It also reduces the emission of carbon monoxide produced by old vehicle engines and thus improves air quality. Another key benefit of bioethanol is the ease of integrating it with the existing road transport fuel system – bioethanol can be easily blended with conventional fuels (up to 15%) without any need for engine modifications.

Applications

Bioethanol can be used in petrol engines as an alternative for gasoline. It can be mixed with gasoline to virtually any percentage. Most of the existing petrol engines operate on blends of up to 15% bioethanol with petroleum.

The higher octane rating of bioethanol than ethanol-free gasoline increases an engine's compression ratio giving increased thermal efficiency. It is also used to fuel bioethanol fireplaces. It is extremely suitable for residential use as it is flueless and does not require a chimney.

Other major applications of bioethanol include the following:

  • Fuel for power generation by thermal combustion
  • Fuel in cogeneration systems
  • Feedstock in the chemicals industry
  • Fuel for fuel cells by thermochemical reactions

Environmental Impacts

Improving the quality of air is one of the most important functions of bioethanol. When added to fuel, bioethanol reduces the use of cancer-causing gasoline compounds such as ethylbenzene, xylene, toluene and benzene. It also reduces the emissions of small particulates and soot from motor fuels, and greenhouse gas emissions.

Water-saving ethanol plant designs are very common. In addition, the water discharged from these plants is regulated such that the water is environmentally neutral when it leaves the plant.

Certain plants manage and reuse the wastewater generated during the ethanol process. Therefore, it is evident that using bioethanol has a positive effect on ecology, minimizes exhaust gas emissions and improves energy safety and operation of transport facilities.

References

 

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