What is Ethanol?
- Ethanol (ethyl alcohol, EtOH) is a transparent, odourless, colourless liquid. The intoxicating component of beer, wine, and other alcoholic beverages is ethyl alcohol.
- It has a moderately sweet flavour in weak aqueous solution, but a scorching flavour in concentrated concentrations.
- It is also used as a biofuel in a number of places worldwide.
- Large industrial plants are the principal producers of ethanol, while some individuals have chosen to create their own.
- Agricultural crops have been used to produce ethanol for more than a century. Ethanol can be manufactured from a variety of starch, sugar, cellulose, etc.-containing basic materials.
- There are generally three kinds of raw materials that can be used to manufacture ethanol: 1) sugarcane, beets, sweet sorghum, and fruits 2) starchy substances, including corn, milo, wheat, rice, potatoes, cassava, sweet potatoes, etc. 3) cellulose-based materials such as wood, paper waste, crop wastes, etc.
- The majority of the third type of materials consists of biomass. Recently, biomass has been recognised as an essential biological resource for ethanol production.
The molecular formula for ethanol is C2H6O, which indicates that it contains two carbon atoms and one oxygen atom. The hydroxyl group (-OH) at the end of the two-carbon chain is denoted by the structural formula for ethanol, C2H5OH.
Properties of Ethanol
- Ethanol is always a liquid at normal temperature, with a melting point of 156K and a boiling point of 351K.
- It is one of the most active constituents in all alcoholic drinks.
- As a particularly effective solvent, it is also employed in the production of a variety of pharmaceuticals, including cough syrups, tonics, and iodine tincture.
- Any percentage of ethanol is suitably soluble in water.
- Additionally, the use of even a small amount of pure ethanol is fatal.
- Consumption of alcohol for a lengthy period generates harmful health effects.
Manufacture of Ethanol
- Ethanol can be manufactured using either chemical synthesis or fermentation.
- Prior to circa 1930, fermentation was the primary method of alcohol production.
- In 1939, for instance, 75% of the ethanol produced in the United States was via fermentation, whereas in 1968, over 90% was created by synthesis using catalytic ethylene hydration.
- Due to the rising cost of crude oil, the source of ethylene used in alcohol synthesis, the global focus has shifted to fermentation-based alcohol production.
Microbial production of Ethanol
- Currently, microbial synthesis of ethanol from organic feedstocks and plant compounds like molasses is used for ethanol production.
- Initially, alcohol was made through fermentation, but for many years, it was manufactured chemically using the catalytic hydration of ethylene.
- In the modern period, microbial fermentation has been utilised to produce ethanol for chemical and fuel applications.
- Today, sugar beets, potatoes, cassava, com, and sugar cane are utilised to make ethanol.
- In industrial ethanol production, both yeasts (Saccharomyces cerevisiae, S. uvarum S. carlsbergensis, Candida brassicae, C. utilis, Kluyveromyces fragilis, and K. lactis) and bacteria (Zymomonas mobilis) have been utilised.
- Saccharomyces cerevisiae is used in the commercial manufacture of alcohol. On the other hand, S. uvarum has also been utilised extensively. Since Candida utilis ferments pentoses, it is utilised for the fermentation of waste sulphite liquor.
- Recent experiments with Schizosaccharomyces have produced encouraging results. When milk whey is used, the K. fragilis strain is recommended for ethanol synthesis. Fusarium, Bacillus, and Pachysolen tannophilus (yeast) can also convert pentose carbohydrates into ethanol.
- Notable is that yeast is inhibited by ethanol at high concentrations. Consequently, the concentration of ethanol reduces the development rate of yeast, which impacts ethanol biosynthesis.
- The bacteria Zymomonas mobilis has greater osmotic tolerance to higher sugar concentrations than yeast. It has a reasonably high ethanol tolerance and a more specific growth rate.
1. Preparation of Medium
- Three types of substrates are utilised in the manufacturing of ethanol: (a) starch-containing substrates, (b) sugarcane juice, molasses, or sugar beet juice, and (c) waste products from wood or wood processing. The production of ethanol from whey is not economically viable.
- Because yeast does not contain amylases, starch must be hydrolyzed prior to its usage. To obtain reducing sugars, it is combined with celluloses of microbial origin following hydrolysis. About one kilogramme of starch required one litre of amylases and three and a half litres of glucoamylases. The following steps are required to convert starch to ethanol.
- Alternatively, if molasses is utilised for ethanol production, bagasse can also be fermented into ethanol.
- Several other nonconventional sources of energy, including aquatic plant biomass and wood following cellulose hydrolysis, produce ethanol.
- Sulphite waste-liquor, a byproduct of paper manufacturing, contains both hexose and pentose sugars. The former can be easily transformed by microorganisms.
- Ethanol is created through a continuous fermentation process. Therefore, massive fermenters are utilised for the continuous production of ethanol. The procedure differs from country to country. India, Brazil, Germany, and Denmark each have their own ethanol producing technologies.
- The fermentation conditions are nearly identical (pH 5, 35°C), but the cultures and culture conditions vary. The fermentation process typically lasts several days, but production begins within 12 hours.
- After fermentation is complete, the cells are separated to obtain yeast cell biomass, which is used as animal feed single cell protein (SCP). To recover ethanol, the culture medium or supernatant is treated.
- Batch fermentation is also used to create ethanol, as there is no discernible difference between batch and continuous fermentation.
- As indicated previously, Saccharomyces cerevisiae begins making ethanol at a rate of 10% (v/v) with 10-20g cells dry weight/lit within 12 hours. The reduction in fermentation time is achieved through the continual recycling of cells during fermentation.
- Up to 95% of ethanol can be recovered by multiple distillations. To achieve 100 percent, an azeotropic mixture comprising 5 percent water must be created.
- After distillation, 5% of the water is removed from an azeotropic mixture of ethanol, water, and benzene.
- In this process, benzene-water-ethanol and an ethanol-benzene azeotropic combination are separated in order to obtain absolute alcohol.
General procedure for production of ethanol from Sugarcane
Regardless of whether ethanol is produced in mass quantities or in a backyard, the basic steps are the same.
- Acquiring the crop or plant.
- This is converted to sugar.
On industrial scale, ethanol is created through the fermentation of molasses. Molasses is the mother liquor remaining after sugarcane juice crystallisation. It is a dark tinted viscous liquid. Molasses comprises around 60% fermentable sugar.
1. Dilution of molasses
- Molasses is first diluted with water in 1:5 (molasses: water) ratio by volume Addition of
2. Ammonium sulphate
- Molasses is supplemented with ammonium sulphate if its nitrogen level is insufficient to supply yeast with sufficient nitrogen.
3. Addition of sulphuric acid
- The fortified molasses solution is next acidified with a little amount of sulfuric acid.
- The addition of acid promotes the growth of yeast but discourages the growth of insignificant bacteria.
- The resultant solution is added to a big tank at a temperature of 35°C and stored for two to three days.
- During this time, yeast-present enzymes sucrose and zymase transform sugar into ethyl alcohol.
- C12H22O11 + H2O → C6H12O6 + C6H12O6
- C6H12O6 → C2H5OH + 2CO2
5. Fractional distillation
The alcohol produced by fermentation is known as “wash” and is around 15 to 18 percent pure. Using fractional distillation, it is turned into rectified spirit or commercial alcohol, which contains 92% pure alcohol. The steps involved in producing ethanol from various feedstocks are as follows. I) Feed formulation 2) fermentation 3) distillation 4) dehydration followed by 5) denaturation.
i. Feed preparation
- The first stage in ethanol production is preparing the feedstock for fermentation. Cereal grains such as corn, rye, rice, barley, soybeans, and wheat, as well as plants such as sugar cane, are the primary sources of fermentation feedstocks.
- Some farmers utilise starch-rich vegetables, such as potatoes. There are a variety of procedures used to prepare the feedstock for fermentation.
- All of the methods ultimately result in a liquid solution containing fermentable carbohydrates.
- These solutions are clarified and cooked at a high temperature for 20 to 30 minutes in order to eliminate bacterial levels that could compromise the process’s effectiveness.
- After undergoing this procedure, the liquid mixture is extracted and fermented.
- If sugar cane is utilised as a raw material, the resulting liquid is known as sugarcane juice or molasses.
ii. Fermentation of sugars
- Yeast cells are added to the previously-obtained liquid mixture in order to initiate the fermentation process.
- Yeast enzyme Zymase transforms simple carbohydrates into ethanol and carbon dioxide.
- During fermentation, the yeast’s enzymatic process produces primarily ethanol, carbon dioxide, and heat.
- In reality, the fermentation reaction is quite complex, and the end product is comparable to beer or wine.
- The impure yeast culture generates variable amounts of other compounds, such as glycerin, methanol, and different organic acids. Following fermentation, the liquid is distilled to separate the alcohol from the water.
- The concentration of ethanol produced by fermentation ranges from a few percent to around 14 percent, with the remainder being water and other components.
- The boiling point of ethanol (78.4 degrees Celsius) is slightly lower than that of water (100 degrees Celsius).
- Due to the small variation in their boiling points, these substances cannot be entirely separated during distillation.
- In its place, an azeotropic mixture (consisting of 96% ethanol and 4% water) is produced.
- Azeotrope alcohol mixtures cannot be further concentrated during distillation. Using distillation, Rectified Spirit (RS, 94%v/v ethanol) is produced.
iv. Dehydration of Alcohol
- 96% of ethanol forms an azeotrope with water, allowing distillation to produce pure alcohol (vlv).
- By dehydrating rectified spirit, ethanol or absolute alcohol can be made. a) Azeotropic distillation and b) Molecular Sieve Technology are commercially available techniques for dehydration of rectified spirit.
Uses of Ethanol
- Use as a chemical feedstock: Due to its high reactivity, ethanol is used as an intermediate in numerous chemical processes in the chemical industry. Thus, it is a crucial chemical feedstock.
- Solvent use: Ethanol is commonly employed in the industrial sector as a solvent for colours, oils, waxes, explosives, cosmetics, etc.
- General utility: Alcohol is used as a disinfectant in hospitals, for cleaning and lighting in the home, and is second only to water as a solvent in laboratories.
- Fuel: Up to 10% ethanol is blended with petrol or gasoline to create gasohol, a fuel used in automobiles.
How do living beings get affected by alcohol?
- When a high quantity of ethanol is drunk, metabolic activities are slowed down. It depresses the central nervous system as well.
- This ultimately results in decreased coordination, sleepiness, etc. Similar to ethanol, consuming a small amount of methanol can result in death.
- In the liver, methanol oxidises into methanal.
- Rapidly reacting with the cells of the human body, methanal causes the coagulation of protoplasm, similar to how eggs are coagulated.
- To avoid the industrial misuse of ethanol, a deadly chemical, such as methanol, is added to make it unfit for consumption.
- The process of adding methanol to ethanol to render it undrinkable is known as denaturing.