3.12 describe the dehydration of ethanol to ethene, using aluminium oxide.

Dehydration of Ethanol

Ethanol can be dehydrated by passing ethanol vapour over hot aluminium oxide (catalyst):

C₂H_5­OH à C₂H₄ + H₂O

3.11 evaluate the factors relevant to the choice of method used in the manufacture of ethanol, for example the relative availability of sugar cane and crude oil

Fermentation vs Hydration of Ethene

	Fermentation	Hydration of Ethene
Raw Materials	Use renewable sources	Uses non-renewable crude oil
Type of process	Batch process	Continuous process
Rate of reaction	Very slow	Fast
Quality of Product	Produces a dilute solution of ethanol that needs processing for pure ethanol	Produces pure ethanol
Reaction conditions	Low temperatures required	High temps and pressures means increased cost

The method chosen depends on many factors:

• If you have a climate suited to growing sugar cane then fermentation's better but if crude oil is more widely available then hydration of ethene is better.
• If a dilute solution of ethanol is required for the production of wine or vinegar then fermentation is better
• If pure ethanol is required is required for a solvent then the hydration of ethene would be better.

3.10 describe the manufacture of ethanol by the fermentation of sugars, for example glucose, at a temperature of about 30°C

Production of Ethanol

Ethanol can be produced in two ways - fermentation or direct hydration of ethene.

Fermentation:

1. Dissolve sugar or starch in water and add yeast
2. Leave the mixture to ferment at 25-40°C for several days - anaerobically
3. Filter off the excess yeast to obtain a dilute solution of ethanol

When the ethanol content reaches around 15% then the yeast is killed.

If you need a more concentrated solution then this must be fractionally distilled.

NB - the enzymes in the sugar produce glucose and then convert it into ethanol.

Sugar / Starch à C₆H₁₂O₆

C₆H₁₂O_{6 ­}à 2C₂O₅OH + 2CO₂

3.9 describe the manufacture of ethanol by passing ethene and steam over a phosphoric acid catalyst at a temperature of about 300°C and a pressure of about 60–70 atm

Production of Ethanol

Ethanol can be produced in two ways - fermentation and direct hydration of ethene.

Hydration of Ethene:

1. A mixture of ethene and steam is passed over phosphoric acid catalyst at a temperature of 300°C and 60-70 atmospheres pressure. 

C₂H₄ + H₂O à C₂H₅OH

1. The ethanol is condensed as a liquid
2. The ethene required for this reaction is obtained from crude oil.