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Greenhouse gas emissions, especially carbon dioxide (CO2), caused by the burning of fossil fuel is considered to be the major contributor to global warming. Concerning about the dependence on fossil fuels and increasing global warming, the search for renewable energy sources that reduce carbon dioxide (CO2) emissions becomes a matter of widespread attention. Thus, to reduce CO2 emissions, renewable energy sources such as ethanol have been seen as a promising alternative to fossil fuel consumption. Bioethanol fuel is also associated with a concept of “green” energy ( sources of energy that contribute to the reduction of greenhouse gas emissions and other environmental impacts). Biofuel like Bioethanol is a promising renewable source produced from fermentation of agricultural crops (sugarcane, sugar beet, corn, wheat) and cellulosic and lignocellulosic feedstock. So, the invention of bioethanol was considered as a great accomplishment to reduce the massive usages of fossil fuels as it transform waste biomass to fuel energy. In this review article we study various sources of plant-based waste feed stocks as the raw materials for bioethanol production, and its use as a fuel in the transportation sector with potential substitutes for blending ethanol with gasoline and its usage to correctly evaluate potential environmental advantages and disadvantages.

To review the use of Bioethanol as a fuel as it is ecofriendly, reduce the dependence on fossil fuel which is harmful for the environment.

Journals, Books, Research articles, Review articles.

Classification of Bioethanol Production

Currently, industrial bioethanol production is divided into different generations based on the type of feedstock used. 

First generation Bioethanol 

Through the fermentation of biomass containing high levels of starch (e.g., wheat, corn) and/or sugar (e.g., sugar cane, sugar beet)  First-generation bioethanol is derived The industrial production of fuel and potable ethanol using first-generation technology is widely practiced commercially in many countries, although the preferred feedstock varies. The most common feedstock in India and Brazil is sugarcane [8]. In, United States corn is the common feedstock [9], while in Canada both corn and wheat are widely used [10]. and in Europe, the ethanol industry most commonly uses potatoes, wheat, and sugar beets [11]. However ethanol produced by first-generation technology and feedstocks is criticized for the consumption of crops which might otherwise be used as food for human or feed for animal consumption [12].

Second generation Bioethanol

Feedstocks like Lignocellulosic biomass sources that are predominantly composed of cellulose, hemicellulose, and lignin are used to derive second-generation bio ethanol. These molecules often form highly recalcitrant structures due to their strong covalent bonds and extensive van der Waal and hydrogen bonding, so pre treatment processes must be implemented to disrupt lignocellulose structures prior to begin biorefinery and fermentation processes [13,14]. Typical pre treatments can include physical (e.g., milling, temperature, ultrasonication), chemical (e.g., acid and alkaline treatments, organic solvent treatments), physicochemical (e.g., steam or CO2 explosion treatments), or biological (e.g., enzymatic hydrolysis) processes.[15] 

Third generation Bioethanol 

Algal biomass or microalgae are used to derive third-generation bioethanol production [16]. Employing algae as a bioethanol feedstock can be advantageous, as algae can rapidly absorb  carbon dioxide, accumulate high concentrations of lipid and carbohydrates, be easily cultivated, and require less land than terrestrial plants [17]. Like second-generation bioethanol, third-generation bioethanol production also requires pre treatment to disrupt algal cells. Such treatments can involve chemical (e.g., acid treatments) or physical (e.g., mechanical forces) pre treatment processes that destroy or disrupt algal cell walls [18].

Fourth generation Bioethanol 

Genetically engineered organisms (e.g., yeasts and algae) are used to derive fourth generation bioethanol in combination with other methods of improving fermentations such as high-yielding biomass (with low lignin and cellulose contents) [19]. Another example of fourth-generation bioethanol production is electro-fermentation, in which electrical energy is used to help regulate respiration in genetically engineered algae through the transfer of electrons [20]. These methods are not currently used by industry and represent a substantial shift away from the more traditional bioethanol production processes. 

Fig.1. Overview of the process steps in the production of (A–C) first-generation ethanol from starch by (A) dry and (B) wet processes and from (C) sugarcane and the production of (D) second-generation ethanol from lignocelluloses. The dry and wet mill processes differ on the number of final value-added products [3]. SHF, separate hydrolysis and fermentation; SSF, simultaneous saccharification and fermentation.[21]

Bioethanol – To be used as a fuel

The use of bioethanol as a fuel for internal combustion engines, either alone or in combination with other fuels, has been given major attention majorly because of its possible environmental and long-term economical advantages over fossil fuel.[22]

The use of ethanol as an automobile fuel is as old as the invention of the internal combustion engine itself. Ethanol was researched upon as an automotive fuel by Nikolas A Otto in 1897 during his initial engine studies. Brazil has been using this fuel since 1920s. Ethanol can be mixed with petrol(fuel) in any concentration up to pure ethanol (E100). Anhydrous ethanol, that is, ethanol without water, can be mixed with petrol in varying quantities to decrease the consumption of petroleum fuels, as well as to decrease air pollution. Ethanol, a biofuel, provides advanced quality, high octane for exceptional engine performance and reduced emissions. Ethanol has been used in vehicles since Henry Ford designed his 1908 Model T to operate on alcohol.

Bioethanol serves mostly in the transportion sector as a constituent of blend with gasoline or as octane increaser (ethyl tertiary butyl ether (ETBE), consisting of 45% per volume bioethanol and 55% per volume of isobutylene). Bioethanol is combined with gasoline at the volume fractions of 5, 10 and 85% (fuel names E5-E85). A consolidated mix of 85% bioethanol by volume can only be used in flexible fuel cars (FFV), while mixtures of 5 and 10% by volume can be used without any technical modifications.[23]

Globally, the three major factors drive the production of ethanol and its use in the transportation sector, such as :

 1. Demand Enrichment: Governments’ mandate for blending a minimum percentage (%) of ethanol with gasoline fuel and production of ethanol compatible cars and bikes.

 2. Supply Enrichment: Schemes for ethanol production from different feedstocks and encouragement to augment bio-refineries and their capacities.

3. Incentives: Promoting the usage of higher ethanol blends through price incentives (tax relief at the retail level) and tax incentives for cars and bikes compatible with E20 and E85. {9}

Data for 2016 show that the global bioethanol production was 100.2 billion litres. Annual bioethanol production is constantly rising, and the prediction of worldwide bioethanol production and its consumption is an increase to nearly 134.5 billion litres by 2024 (Fig.2) [24].

Predictions of the world bioethanol production (a) and consumption (b) by 2024 .

Bioethanol, as an alternative to the fossil fuels, is mainly produced by yeast fermentation from different feedstocks. It is a high octane number fuel and its physicochemical features are considerably different compared to the gasoline (Table 1) [24]. 

Specification	Gasoline	Ethanol
Chemical formula	CnH2n+2 (n=4–12)	C2H5OH
M/(g/mol)	100-105	46.07
Octane number	88-100	108
ρ/(kg/dm3)	0.69-0.79	0.79
Boiling point/°C	27-225	78
Freezing point/°C	-22.2	-96.1
Flash point/°C	-43	13
Lower heating value.103/(kJ/dm3)	30-33	21.1
Latent vaporization heat/(kJ/kg)	289	854
Solubility in water	insoluble	soluble

Advantages of Bioethanol fuel [25]

1.  Helps in Reducing Global warming

Global warming is caused by the relentless emission of dangerous greenhouse gases from the use of fossil fuels (oil, natural gas, and coal). The effects of global warming are catastrophic including changes in weather patterns, rising sea levels, and excessive heat. The combustion of ethanol fuel only releases carbon dioxide and water. The carbon dioxide released is ineffective regarding environmental degradation. [26]

2. Ethanol Fuel is Cost-effective as compared to Other Biofuels

Ethanol fuel is the least expensive energy source since virtually every country has the capability to produce it. Corn, sugar cane or grain grows in almost every country which makes the production economical compared to fossil fuels.[27]

Fossil fuels can play against the economy of most countries, especially, developing countries that have no capacity to explore them. It, thus, makes sense for these growing economies to dwell on the production of ethanol fuel to dial back on the dependence of fossil fuel in order to save revenue.

3. Easily Accessible

Since ethanol is a biofuel, it is easily accessible to virtually everyone. Biofuel means energy derived from plants like sugarcane, grains, and corn. All tropical climates support the growth of sugarcane. Grain and corn grow in every country. In fact, corn is a staple food in most countries in Africa

4. Environment friendly & Ecologically Effective

One striking advantage of ethanol over other fuel sources is that it does not cause pollution to the environment. Using ethanol fuel to power automobiles results in significantly low levels of toxins in the environment. On numerous occasions, ethanol is converted to fuel by blending with gasoline.

Specifically, ethanol to gasoline ration of 85:15. The little composition of gasoline acts as an igniter, while ethanol takes up the rest of the tasks. This ratio of ethanol to gasoline minimizes the emission of greenhouse gases to the environment since it burns cleanly compared to pure gasoline.[28]

5. Opens up Untapped Agricultural Sector

The fact that ethanol fuel production relies mainly on agricultural produce, individuals will be shoved into the untapped agricultural sector, and this will uplift a countries economy. This act will guarantee ethanol fuel availability for many years. The need for increased production of corn and grains has set the farming industry booming.

6. Reduces Dependence on Fossil Fuels

Harnessing of fuel from corn or biomass is an economical way to sustain any economy and prevent it from over-reliance on the importation of fossil fuels like oil, and gas. Embracing ethanol fuel can save a country a lot of money that can be plowed back into the economy. Since ethanol is domestically produced, from domestically grown crops, it helps reduce dependence on foreign oil and greenhouse gas emissions. If we could run our vehicles on 100% ethanol, the difference would be noticeable.

7. Creates more Job opportunities

When the use of ethanol fuel increases, it means more plantations of sugarcane, corn, and grains. It also means more ethanol fuel processing plants and that translates to job opportunities. Ethanol can also be branched out to produce alcoholic beverages leading to the creation of job opportunities in the hospitality industry.

8. Variety of Sources of Raw Material

Although corn and sugarcane are the chief raw material for producing ethanol fuel, pretty much every crop or plant containing starch and sugar can be used. sugar-containing raw materials: sugar beet, sugarcane, molasses, whey, sweet sorghum, (ii) starch-containing feedstocks: grains such as corn, wheat, root crops such as cassava, and (iii) lignocellulosic biomass. Nowadays algae, microalgae, urban waste are also undergoing research and are used as a raw material.

9. Ethanol is Classified as a Renewable Energy Source

It’s classified as a renewable resource because it’s mainly as a consequence of the conversion of energy from the sun into useful energy. The production of ethanol begins with the photosynthesis process, which enables sugarcane to thrive and later be processed into ethanol fuel.

Disadvantages of Ethanol Fuel [29]

1. Ethanol production requires a Large Piece of Land

We’ve analysed that ethanol is produced from corn, sugarcane, and different grains. All these are crops that need to be grown in farms and require massive land. For ethanol to meet the increasing demand, it must be produced on a massive scale. This, essentially, means that such  crops will have to be grown on a wide scale, which needs vast acres of land.

The problem is that not everyone has that kind of land, so the very option is renting or leasing, which might increase expenses to the budget. This aspect could also lead to the reduction of natural habitats for most plants and animals.

2. Increase in Food Prices

The major ingredient in making ethanol is corn. If the demand for ethanol fuel skyrockets, the price of corn would also rise up, and that would affect the cost of ethanol production. Other users of corn other than for fuel will also suffer, for example, those utilizing corn as an animal feed. Also, the lucrative rates of ethanol fuel could trigger most farmers to abandon food crops for ethanol production, which might also lead to an rise in food prices.

3. The Distillation Process is Not a viable option For the Environment

The process of distilling fermented corn or grain takes a really long time and involves a lot of heat expenditure. The source of heat for distillation is fossil fuel, and such fossil fuels emit a lot of greenhouse gases, which is disadvantageous to the environment.

4. It is quite difficult to Vaporize

Pure ethanol is hard to vaporize. This makes starting a car or a motor bike in cold dry conditions very difficult, which is why a number of vehicle owners make a point to have a little petrol, for instance, E85 cars that use 15% petroleum and 85% ethanol. This is purely for contingency.

5. Requires greater usage of Water

Pure ethanol has a high affinity for water, and it’s able to absorb any trace around it or from the atmosphere. This fact is true for those blends of gasoline and ethanol used to power vehicles. The fact that ethanol has high water attraction capabilities means that it’s very difficult to obtain it in its purest form since there will somehow be a trace of water. In fact, manufacturers normally indicate 99.8% pure ethanol. This is especially dangerous for marine users than regular road car users. When water finds a way into a storage or fuel tank, it goes to the bottom of the tank since water is denser than fuel. This will lead to a plethora of small and big engine problems for your vehicle.  The water attraction property of ethanol is the reason why it’s transported by railroad or auto transport.

Usage of Bioethanol as a fuel in India 

India is the world’s third largest energy consuming nation and a significant part of India’s energy requirement is met through oil which continues to rely on imports largely. India’s share in global energy consumption is set to double by 2050. A rising energy demand and high reliance on import poses significant energy security challenges. It also leads to massive foreign currency outflow. Further, excessive use of fossil fuels leads to higher carbon emissions and associated health concerns. Domestically produced ethanol is a potential opportunity to reduce reliance on oil imports by blending it with conventional fossil fuels for consumption.

In 2008, the Ministry of New & Renewable Energy established a National Policy on Biofuels to limit the country's future carbon footprint and dependence on foreign crude. Under this, the blending level of bio-ethanol at 5 % with petrol was proposed from October 2008, leading to a target of 20 % blending of bio-ethanol by 2017. [30]

During the ethanol supply year 2019-20 about 173.03 crore litres of ethanol was supplied by sugar mills and grain based distilleries to OMCs thereby achieving 5% blending target. The Government has 10% blending target for mixing ethanol with petrol by 2022 & 20% blending target by 2030 and 5% blending of biodiesel in diesel in the whole country by 2030.[31]

On the occasion of World Environment Day, 5 June 2021, report of the “Expert Committee on Roadmap for Ethanol Blending in India by 2025” was released.[32] 

According to the report, 20% ethanol blending is within reach. The report further lays out an annual plan for the gradual rollout of E20 ethanol in the country. It suggests specific responsibilities of Union Ministries, State Governments and vehicle manufacturers for the production, supply and gradual rollout of 20% ethanol blending in petrol by 2025. 

Large benefits can accrue to the country by 20% ethanol blending by 2025, such as saving Rs 30,000 crore of foreign exchange per year, energy security, lower carbon emissions, better air quality, self-reliance, use of damaged foodgrains, increase in farmers' incomes, employment generation, and greater investment opportunities in the nation.  

There are many significant advantages of Ethanol blending, such as increase in Research Octane Number (RON) of the blend, fuel embedded oxygen and higher flame speed. These properties of ethanol help in complete combustion and reduce vehicular emissions such as hydrocarbon, carbon monoxide and particulate matter. The calorific value of ethanol is around 2/3rd of gasoline. This shows that the increase in ethanol content will decrease the heating value of the ethanol-gasoline blend. Therefore, more fuel is required to achieve the same engine power output. However, ethanol has a higher Octane number and thus the engine can be operated with a high compression ratio without knocking. This increases the efficiency of the engine relatively. This combined with optimal spark timing negates the fuel economy debit due to low calorific value of ethanol [33]. Hence, ethanol is considered as an efficient fuel if some suitable modifications are made in the vehicle 

India initiated the use of ethanol as an automotive fuel in the year 2003. The Ministry of Petroleum and Natural Gas (MoPNG) issued a notification in September 2002 in the official gazette for mandatory blending of 5 % ethanol in 9 major sugar producing states and four union territories from 2003. However, despite potential, no significant progress was made under the ethanol programme and the production of ethanol remained stagnated up until recently when transformative reforms were carried out. The results are set to help not only the economy but transform farmers’ income and recharge the rural economy as-[34]

1. Ethanol supplies and blending % have increased more than 5 times in last 6 years i.e. from 50 crore litres to 450 crore litres (1.53% to 8.50%).

2. Also remunerative prices of suppliers have more than doubled in last 6 years – a major boost to farmer’s income i.e. 25.12 Rs/lt. to 62.25 Rs/litres .

3. Ethanol distillation capacities almost doubled 40% in 5 years (157 – 445, no. of distilleries).

Bioethanol production has been improved by new and advanced technologies, but there are still major challenges that need to be further investigated. Challenges like maintaining a steady performance of the genetically engineered microorganisms in commercial scale and fermentation operations and developing more efficient pre-treatment technologies for the lignocellulosic biomass and integrating and viable components into economic ethanol production systems. The share of bio ethanol in the automotive fuel market will grow fast in the coming years due to its environmental merits. India is one of the first pime producers and consumers of sugar worldwide and it is not envisaged for this country to use sugarcane for producing part of its future requirement of bioethanol so Indian production of bio ethanol must be critically analysed in elaborate details in the light of both future oil and ethanol markets. Nowadays Bioethanol production from plant-based waste biomass by yeast fermentation is projected as economically successful and realistic approach for novel biofuel innovation and maximisation by biomass experts all over the world. Significant numbers of commercial industries successfully scaled up their bioethanol generation projects from plant-based feedstocks and initialized a novel source of alternative fuel production and utilization in the market. Additionally, modern motor vehicles run perfectly on bioethanol blends without any engine modification that has led to a cleaner and greener environment and sufficient energy-savings. The following remarks can be concluded from the abovementioned studies, that as a motor fuel, the use of ethanol is not new to us. At times it seems to be a superior fuel than gasoline. Bearing in mind the shorter supply time period of petroleum products in near future, mankind has been constantly trying to find out an alternative as efficient as gasoline. Studies show that ethanol presents humungous opportunities as a biofuel and it can be produced even from the most noxious of weeds. There is a huge scope for research in the field of blending limits and combinations for the alcohol generated from several resources.

1. Xu, J.; Li, M.; Ni, T. Feedstock for bioethanol production from a technological paradigm perspective. BioResources 2015,10, 6285–6304. [CrossRef]. 2. Stoeglehner, G.; Narodoslawsky, M. How sustainable are biofuels? Answers and further questions arising from an ecological footprint perspective. Bioresour. Technol. 2009, 100, 3825–3830. [CrossRef]. 3. Renewable Fuels Association (RFA). Annual Fuel Ethanol Production. 2020. Available online: https://ethanolrfa.org/statistics/annual-ethanol-production/ (accessed on 22 April 2021). 4. Kim, S.; Dale, B.E. Global potential bioethanol production from wasted crops and crop residues. Biomass Bioenergy 2004, 26, 361–375. [CrossRef]. 5. Gnansounou, E., Dauriat, A., 2005. Ethanol Fuel from Biomass: A Review. Journal of Scientific and Industrial Research, Volume 64, pp. 809821. 6. Srivastava, A.K., Agrawal, P., Rahiman, A., 2014. Delignification of Rice Husk and Production of Bioethanol. International Journal of Innovative Research in Science, Engineering and Technology. Volume 3(3), pp. 1018710194. 7. Kim, S.; Dale, B.E. Global potential bioethanol production from wasted crops and crop residues. Biomass Bioenergy 2004,26, 361–375. [CrossRef]. 8. Bioethanol Production from Renewable Raw Materials and Its Separation and Purification: A Review - PMC (nih.gov). 9. https://en.wikipedia.org/wiki/Corn_ethanol. 10. Natural Resources Canada. Ethanol. 2020. Available online: https://www.nrcan.gc.ca/energy-efficiency/transportationalternative-fuels/alternative-fuels/biofuels/ethanol/3493 (accessed on 4 August 2021). 11. Baruah, J.; Nath, B.K.; Sharma, R.; Kumar, S.; Deka, R.C.; Baruah, D.C.; Kalita, E. Recent trends in the pretreatment of lignocellulosic biomass for value-added products. Front. Energy Res. 2018, 6, 141. [CrossRef]. 12. https://www.eubia.org/cms/wiki-biomass/biofuels/bioethanol/ Ribeiro, B.E. Beyond commonplace biofuels: Social aspects of ethanol. Energy Policy 2013, 57, 355–362. 13. Havlík, P.; Schneider, U.A.; Schmid, E.; Böttcher, H.; Fritz, S.; Skalský, R.; Aoki, K.; De Cara, S.; Kindermann, G.; Kraxner, F.; et al.Global land-use implications of first and second generation biofuel targets. Energy Policy 2011, 39, 5690–5702. 14. 14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9535326/. 15. 15. Carriquiry, M.A.; Du, X.; Timilsina, G.R. Second generation biofuels: Economics and policies. Energy Policy 2011, 39, 4222–4234. 16. Singh, A.; Olsen, S.I. A critical review of biochemical conversion, sustainability and life cycle assessment of algal biofuels. Appl. Energy 2011, 88, 3548–3555. [CrossRef]. 17. https://pubs.acs.org/doi/10.1021/es5027689. 18. https://www.mdpi.com/2071-1050/12/23/9980/htm. 19.https://pubs.rsc.org/en/content/articlelanding/2011/ee/c0ee00593b . 20.https://www.researchgate.net/publication/336862610_The_FourthGeneration_ Biofuel_A_Systematic_Review_on_Nearly_Two_Decades_of_Research _from_2008_to_2019. 21.Sciencedirect.com/topics/earth-and-planetary-sciences/bioethanol. 22.https://pubs.rsc.org/en/content/articlelanding/2016/ra/c5ra24983j#:~:text= Bioethanol%20is%20a% 20renewable%20fuel,34%25%20lower%20than%20for%20gasoline. 23. Bioethanol Production from Renewable Raw Materials and Its Separation and Purification: A Review - PMC (nih.gov). 24. cbi.nlm.nih.gov/pmc/articles/PMC6233010/. 25. What is Ethanol Fuel and Advantages and Disadvantages of Ethanol - Conserve Energy Future (conserve-energy-future.com). 26. https://www.nrel.gov/docs/legosti/old/26986.pdf 27.https://www.sciencedirect.com/topics/engineering/ethanolfuel#:~:text= Ethanol%20fuel%20is%20cost% 20effective,economical%20compared%20to% 20fossil%20fuels. 28. https://royalsocietypublishing.org/doi/10.1098/rspa.2020.0351 29.https://www.biotecharticles.com/Environmental-Biotechnology-Article/ Bioethanol-Production-Advantages-Disadvantages-And-Environmental-Impacts-3816.htmlq. 30. Yüksel F, Yüksel B. The use of ethanol–gasoline blend as a fuel in an SI engine. Renew Energy. 2004;29(7):1181–91. 10.1016/j.renene.2003.11.012 [CrossRef] [Google Scholar]. 31. EthanolBlendingInIndia_compressed.pdf (niti.gov.in). 32. Expert Committee on Roadmap for Ethanol Blending in India by 2025 | NITI Aayog. 33. Ethanol as Fuel — Vikaspedia. 34. https://pib.gov.in/PressReleasePage.aspx?PRID=1727206.