Alcohols
Describe the manufacture of ethanol by fermentation and by catalytic
addition of steam to ethene
● Fermentation:
- The fermentation of glucose
- conditions: temperature of about 30˚C, anaerobic conditions (no oxygen) and using the enzymes in yeast
- equation: glucose → ethanol + carbon dioxide
Alcohols – Preparation of ethanol
Fermentation :
This procedure uses yeast and aqueous solution of sucrose. The products are ethanol and carbon dioxide, which leaves of the solution, leaving behind a weak aqueous solution of ethanol.
C6H12O6(aq) → 2 CH6CH2OH(aq) + 2CO2(g)
This solution of ethanol in water can be more concentrated by fractional distillation,
● Steam:
- Reacting ethene with steam
- conditions: phosphoric acid catalyst, temperature of about 300˚C and a
pressure of about 60-70 atm - equation: ethene + steam → ethanol
Hydration of ethene :
The fermentation of sucrose is slow and does not produce enough ethanol. That’s why we need a different process.
Ethene is mixed with steam and passed over a catalyst consisting of solid silicon dioxide coated with phosphoric(V) acid. The temperature used is 300°C and the pressure is about 60 to 70 atmospheres.
CH2=CH2(g) + H2O(g) → CH3CH3(g
(Extended only) Outline the advantages and disadvantages of
these two methods of manufacturing ethanol
● Fermentation
o Advantages
▪ Renewable raw materials
▪ Warm, normal pressure (inexpensive)
▪ Little energy needed
o Disadvantages
▪ Batch process (stop-start)
▪ A lot of workers needed
▪ Slow
▪ Impure – needs treatment
● Steam
o Advantages
▪ Continuous process (runs all the time)
▪ Few workers needed
▪ Fast
▪ Pure
o Disadvantages
▪ Non-renewable raw materials
▪ High temperature and pressure (expensive)
▪ A lot of energy needed
Describe the properties of ethanol in terms of burning
● Burning in air or oxygen (complete combustion)
o CH3CH2OH + 3O2==> 2CO2 + 3H2O
o Can be used as a fuel in this way (this reaction produces heat energy)
o Burns in a good supply of oxygen
Name the uses of ethanol as…
● A solvent
● A fuel