industrial chemistry:- Ethanol

uses of ethanol

• synthesis of acetaldehyde and ethylene

• used as a solvent

• important reactor for ether synthesis

• important gasoline additive (ethanol blending: current target in india is 10%)

• carbon source for single cell protein

worldwide production stats

• Synthetic production in 1998: 2.6*106 tonnes per year

• By fermentation of agricultural products (sugarcane molasses and corn starch) in 1997: 24.1*106 tonnes per year.

production by synthetic methods

1. by indirect hydration, addition of H₂SO₄ and subsequent saponification of sulfuric acid ester

2. by direct catalytic hydration

indirect hydration

synthesis of ethanol requires conc H₂SO₄ (94-98% purity) for that purpose submerged burners are used to evaporate water form commercially available dil. H₂SO₄

Disadvantage: -

1. corrosion problems

2. concentrating H₂SO₄ is an expensive process

3. submerged burner produces SO₂ as a side product

catalytic direct hydration

addition of water is carried out in gas phase and acid catalyst used is H₃PO₄

/SiO₂

the synthesized ethanol is isolated from dilute aqueous solution

1. H₂O azeotrope distillation

2. H₂O removal by adding entraining agent like benzene: - increases volatility of water

disadvantages

1. C₂H₄ conversion is low (abt 4%)

2. high purity ethene required

3. continuous loss of H₃PO₄

4. high energy consumption

production of ethanol from sugarcane

1. procuring the grain or the plant

2. converting this to sugar

3. fermentation

4. distillation

industrial scale production of ethanol

fermentation of molasses

• molasses is the mother liquor left after crystallization of sugarcane juice

• dark colored viscous fluid

• contains abt 60% fermentable sugar

process of industrial scale production of ethanol

1. dilution of molasses: molasses is first diluted with water in 1:5 molasses: water ratio by volume

2. ammonium sulphate: if nitrogen content of the molasses is less, it is fortified with ammonium sulphate to provide adequate supply of nitrogen to yeast

3. addition of sulfuric acid: fortified solution of molasses is then acidified with small quantity of sulfuric acid. addition of acid favors growth of yeast but unfavors growth of useless bacteria

4. Fermentation The resulting solution is received in a large tank and yeast is added to it at 35°C and kept for 2

   to 3 days. During this period, enzymes sucrose and zymase which are present in yeast, convert sugar into ethyl alcohol

5. Fractional distillation: Alcohol obtained by fermentation is called wash which is about 15-18% pure. by using fractional distillation, it is converted to 92% pure alcohol, known as rectified spirit or commercial alcohol.