Production of Ethanol

• Ethanol can be produced from 2 different ways

  • Hydration 
  • Fermentation
• Hydration

  • Ethene is reacted with steam 
  • This is done using a temperature of 300°C , pressure of 70 atmospheres and a phosphoric acid catalyst to speed up the rate of reaction
  • This produces ethanol

  
• How can the yield of ethanol from Hydration be increased?

  • The hydration reaction is reversible
  • So any unreacted ethene and steam are passed back through the phosphoric acid catalyst  
  • This increases the yield of ethanol

  
• Advantages of Hydration

  • The atom economy for the hydration reaction is 100% 
  • The hydration of ethene is an addition reaction - all the reactant atoms end up in the desired product 
  • Hydration produces a high yield of ethanol 
• Disadvantages of Hydration

  • The reaction requires a high temperature 
  • This means the reaction requires a lot of energy 
  • The ethene for this reaction comes from crude oil , which is non-renewable
• Fermentation

  • Start with a sugar solution such as glucose and mix it with yeast 
  • The temperature should be around 30°C and the reaction should take place in anaerobic conditions (without oxygen)
  • The yeast will convert the sugar solution into an aqueous solution of ethanol 
  • Carbon dioxide gas is also produced

  
• Why do we need to purify the product of Fermentation?

  • The product of fermentation is an aqueous solution of ethanol (ethanol dissolved in water) 
  • The ethanol needs to be purified by distillation 
  • This requires a lot of energy

  
• Advantages of Fermentation

  • Low temperature means that the reaction does not require a lot of energy 
  • The sugar from this reaction comes from plants and is therefore renewable
• Disadvantages of Fermentation

  • Low atom economy - only about half of the atoms in the reactants end up in the desired product 
  • The ethanol needs to be purified by distillation and this requires a lot of energy