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Industrial Methods of Synthesis of Ethanol: Introduction, Structure of Ethanol, Industrial methods for synthesising Ethanol, Uses, Practice problems & FAQs

Industrial Methods of Synthesis of Ethanol: Introduction, Structure of Ethanol, Industrial methods for synthesising Ethanol, Uses, Practice problems & FAQs

We are all aware of how crucial hand sanitisers were during the COVID-19 pandemic.

Do you know what the sanitising substance is in these hand sanitisers?

It is mostly ethyl alcohol or sometimes propyl or isopropyl alcohol. The concentration of ethyl alcohol or ethanol varies from a minimum of 60% to a maximum of 95% v/v with water. The higher the concentration of alcohol, the more effective its action against bacteria, microorganisms and viruses.

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Ethanol is a very good sanitiser not only for hands but also for pathogen-contaminated laboratories, medical equipment, wounds etc.

Ethanol has antibacterial properties because it can slow or stop the growth of microorganisms (germs). The protein structure of the microorganisms is altered, which prevents them from performing their intended functions. A process known as denaturation occurs when the bonds holding the protein molecules together to maintain their unique shape are severed, which causes a protein to lose its shape. As a result, hand wipes and hand sanitisers both contain ethanol.

In addition to the use mentioned above, ethanol is used as a solvent to dissolve a variety of organic compounds that are insoluble in water. It is an ingredient in perfumes, detergents, inks, paints, and cosmetics.

We will get to know more about ethanol and how it is prepared industrially on this concept page.

Table of Contents:

  • Ethanol - Introduction
  • Structure of Ethanol
  • Industrial Methods of the Synthesis of Ethanol
  • Uses of Ethanol
  • Practice Problems
  • Frequently Asked Questions(FAQs)

Ethanol - Introduction

A molecular formula is a short form of the structural elements that make up any chemical compound.

We will go over some fundamental IUPAC nomenclature rules in order to determine the systematic naming of alcohols.

The prefix of the given compound, ethanol, is "eth," which, according to IUPAC, stands for the name of any compound with two carbon atoms in the main parent chain. So, ethanol contains two carbon atoms.

Alcohol is the primary functional group present in this statement, as is clear from the suffix since it is '-ol'. This demonstrates that a hydroxyl group (OH) has taken the place of one hydrogen atom.

As a tetravalent atom, carbon should fill the remaining valency with an atom of hydrogen. Therefore, a parent chain of two carbon atoms should contain six hydrogen atoms.

Hence the molecular formula of ethanol is C2H5OH or C2H6O.

Structure of Ethanol:

Ethanol has the chemical formula C2H6O, which has one oxygen atom, six hydrogen atoms and two carbon atoms. The structural formula for ethanol C2H5OH, provides a little more information by demonstrating that the 2-carbon chain ends in a hydroxyl group (-OH). Following is the ethanol's structure:

Industrial Methods of the Synthesis of Ethanol:

1. Fermentation of sugar(Saccharine) containing carbohydrates and molasses.

The fermentation method manufacture of ethanol involves two steps-

a). Enzymatic hydrolysis of carbohydrates and molasses in the presence of yeast and

b). Distillation of alcohol.

a). Enzymatic hydrolysis of carbohydrates.

This is the most preferred method of production in sugarcane-growing countries. Ethanol is manufactured by the fermentation of molasses.

After the removal of sugar from the sugarcane juice by crystallisation method, the filtrate is a dark-coloured viscous liquid called mother liquor. The mother liquor still contains about roughly 60% fermentable sugar and also referred to as molasses. Molasses from cane sugar contains mainly sucrose- a disaccharide carbohydrate.

Fermentation is a chemical process involving the effervescence of carbon dioxide and the release of heat, brought about by pathogens that can degrade organic compounds under oxygen-poor conditions (anaerobic). The pathogens feed on these organic materials by producing enzymes ( biological catalysts). As these reactions involve breaking down the molecule in the presence of water, fermentation is an enzymatic hydrolysis reaction.

Enzymatic hydrolysis of molasses involves many steps-

(i) Molasses dilution:

The enzymes show maximum activity only in dilute solutions and hence the first step involves the dilution of molasses to a 1:5 (molasses: water) volume ratio with water.

(ii) Ammonium sulphate fortification: The pathogens growth needs carbon and nitrogen inputs. While the molasses can satisfy their carbon need, the nitrogen requirement is fortified externally by the addition of nitrogen compounds like ammonium sulphate.

(iii) Sulphuric acid addition: A little amount of sulphuric acid is added to the fortified molasses solution. Acidification inhibits the growth of harmful and interfering other pathogens and allows the growth of only yeast (fungi).

(iv) The addition of Yeast

Yeasts is a eukaryotic (cells having membrane-covered organelles) microorganisms. They are classified into saccharomyces and non-saccharomyces groups.

Non-saccharomyces yeasts are useful in the fermentation of up to 4 to 5 % of ethanol production and at higher concentrations of ethanol, it becomes inactive. The saccharomyces strains are resistant to ethanol poisoning and are active to produce about 18 % concentrated ethanol solution.

Invertase enzyme produced by the yeast hydrolyses the sucrose in the molasses to a mixture of glucose and fructose.

Another enzyme, Zymase also produced by Yeast breaks down the glucose into ethanol and carbon dioxide.

After the addition of yeast, fermentation is a slow process and allowed to go for a few days, at around 300K. The final fermented liquor containing the alcohol is called ‘wash’ and is sent for distillation of alcohol.

b). Fractional distillation: Fractional distillation is now used to remove the alcohol from the fermented liquid, which contains 15 to 18 per cent alcohol and the remaining water. On distillation, an azeotropic mixture containing 95.5 per cent ethanol and 4.5 per cent water is obtained. It's known as the rectified spirit. Then, for about 5 to 6 hours, this mixture is heated under reflux over quicklime. After that, it is left to stand for 12 hours. 100 % pure alcohol is produced after distilling this mixture. It is called absolute alcohol.

2. Fermentation of starchy materials

Many kinds of cereal like rice, barley, wheat, rye and tapioca, potatoes are a rich source of starch. Starch also can be fermented to yield alcohol.

Starch is converted into glucose in a two-step process using two enzymes. The alpha-amylase enzyme helps in the breakdown of the long starchy mass into smaller pieces in the presence of water during a process called liquefaction. The glucoamylase enzyme converts the smaller pieces into glucose units and the process is called saccharification.

Germinated cereals called malt contain diastase enzymes. A diastase is a group of amylases. The enzyme converts the starch to maltose- a carbohydrate. Maltase enzyme converts maltose into glucose.

The glucose liquor is fermented with yeast to ethanol.

3. Fermentation of Cellulosic material

Biomasses like husks of rice, wheat, grass, and bagasse, after preliminary treatment can be fermented with ethanologenic bacteria like clostridium, and zymomonas to form ethanol.

4. From Ethylene:

Ethene being an unsaturated compound undergoes addition reactions. Ethylene takes one molecule of water under acidic conditions to form ethanol.

In order to hydrate ethylene, a mixture of ethylene and a substantial excess of steam (H2O) is passed over an acidic catalyst, such as a phosphoric acid catalyst, at high pressure (60 atm) and temperature (300o C).

Uses of Ethanol:

  • Among other things, ethanol is used as an antiseptic, a polar solvent in chemical synthesis, a neurotoxin, a disinfectant, a teratogen, and an Escherichia coli metabolite. It also has the ability to depress the central nervous system.
  • Ethanol is a type of fuel. Although it cannot be used entirely as fuel due to its water absorption properties, which can cause engine damage, it is an environmentally friendly fuel. If scientists can extract enough value from ethanol as a fuel, it could be a great alternative to traditional fuels that pollute the environment.
  • Alcoholic beverages use ethanol when properly diluted. Additionally, organic chemistry and chromatography both use ethanol as a reagent. It serves as a solvent in the industry as well.
  • It's used to make denatured alcohol, medications (rubbing compounds, lotions, tonics, and colognes), perfumery, and octane enhancers for gasoline.
  • The inhibitory effects of GABA at the GABA-A receptor are amplified by ethanol, a potent CNS depressant. Gamma-aminobutyric acid is known as GABA.
  • Production of dopamine and serotonin is increased by ethanol.
  • Myocardial infarction risk is decreased by moderate ethanol consumption.

Practice problems:

Q1. Which enzyme is employed in the fermentation process to hydrolyze starch into maltose and produce ethanol?

(A) Diastase
(B) Beta-Amylase
(C) Lipase
(D) Alpha-Amylase

Answer: (A)

Solution: Starch is broken down into maltose by diastase. An enzyme called lipase catalyses the hydrolysis of lipids. Amylase converts starch from complex carbohydrates.

Q2. As the length of the hydrocarbon chain in alcohol increases, solubility

(A) Decreases
(B) Increases
(C) Remains the same
(D) None of the above

Answer: (A)

Solution: Consider the following scenario involving 5-carbon alcohol molecules. When hydrocarbon chains are squeezed between water molecules, hydrogen bonds are broken. The alcohol molecules' -OH ends can form new hydrogen bonds with water molecules, but the hydrocarbon "tail" does not. As a result, many of the original hydrogen bonds that are broken are never replaced with new ones.

Van der Waals dispersion forces between the water and the hydrocarbon "tails" replace the original hydrogen bonds. These attractions are much weaker and unable to compensate for the broken hydrogen bonds. Even taking into account the increased disorder, the process becomes less feasible. This situation worsens as the length of the alcohol increases, and thus the solubility decreases.

Q3. When making ethanol, the pH of the molasses solution should be

(A) 1-2
(B) 4-5
(C) 7-9
(D) 2-3

Answer: (B)

Solution: For yeast to grow and produce invertase and zymase, the pH of the molasses solution needs to be between 4-5. The addition of sulfuric acid adjusts the pH.

Q4. As the length of the chain in alcohol increases, the boiling point of alcohol

(A) Decreases
(B) Increases
(C) Remains the same
(D) None of the above

Answer: (B)

Solution: Alcohols are subject to other intermolecular forces in addition to hydrogen bonds. Additionally, they encounter dipole-dipole interactions and van der Waals dispersion forces. All alcohols exhibit hydrogen bonding and dipole-dipole interactions in a similar manner, but as alcohols get bigger, dispersion forces get stronger. As the molecules lengthen and accumulate more electrons, these attractions become stronger. The size of the created temporary dipoles grows as a result. Because of this, as the number of carbon atoms in the chains rises, so do the boiling points. The boiling points increase because it requires more effort to overcome the forces of dispersion.

Frequently asked questions(FAQs)

Q1. Why is ethanol so intoxicating to humans?
Answer:
Ethanol is an intoxicating substance. When people consume ethanol, their liver cannot purify or filter it all at once. As a result, it travels to various parts of the body, including the brain. When ethanol enters the brain, it obstructs the gaps that exist between neurons. People become slower and slower as their neurons fail to function properly. Their words become slurred, and their bodies are unable to maintain proper motor neuron function. Furthermore, drinking alcohol activates the brain's reward centre, causing dopamine to be released. This tricks the brain into believing that ethanol is beneficial because it makes people happy. And people continue to consume ethanol.

Q2. Is ethanol soluble in water?
Answer:
Small alcohols are completely soluble in water; mixing the two produces a single solution in any proportion. The solubility, however, decreases as the alcohol's hydrocarbon chain lengthens. The decrease in solubility is noticeable at four carbon atoms and beyond; when the two are mixed, a two-layered substance may appear in a test tube.

Consider ethanol as an example of small alcohol. The main intermolecular attractions in both pure water and pure ethanol are hydrogen bonds. Hydrogen bonds between water molecules and hydrogen bonds between ethanol molecules must be broken in order to combine the two. Both of these processes require energy. However, when the molecules are combined, fresh hydrogen bonds are made between the molecules of water and ethanol.

The energy released when these new hydrogen bonds form approximates the energy required to break the original interactions. Furthermore, there is an increase in the system's disorder or entropy. This is another factor that influences whether or not chemical processes occur.

Q3. What is gasohol?
Answer:
Due to its complete combustion, ethanol is a clean fuel. It produces water and carbon dioxide with a clear, smokeless flame, so it does not greatly increase pollution.

2 C2H5OH + 6 O2  6 H2O+ 4 CO2

Gasohol, is a blended fuel containing, about 10%–20% of ethanol with gasoline or petrol.

Q4. What kind of solvent—polar protic or polar aprotic—is ethanol?
Answer:
Because of the presence of the -OH bond, ethanol falls under the category of polar protic solvent. A polar solvent contains a hydrogen atom that is linked to a more electronegative atom than hydrogens, such as oxygen or nitrogen. Hydrogen atoms are given to other polar molecules that contain oxygen or nitrogen atoms. Because these electronegative atoms have a single pair of electrons, they participate in sharing and, as a result, form a bond with the hydrogen atom.

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