The contact process

• The contact process is used to make Sulfuric acid (H2SO4)
• sulfur + oxygen ->  sulfur dioxide

  sulfur dioxide + oxygen ⇌  sulfur trioxide

  sulfur trioxide + water ->  sulfuric acid
• Conditions for contact process

  • Temperature
  • Oxidising sulfur dioxide to form sulfur trioxide is exothermic, therefore to increase the yield, the temperature should be reduced (equilibrium shifts right)
  • However, this would reduce the rate of reaction, therefore a compromise of 450C is used.
• Conditions for contact process

  • Pressure
  • 2SO2 + O2 ⇌ 2SO3
  • 2 moles of gas on the product side (2SO3) compared to 3 moles on the reactants die (2SO2 + O2), therefore to get a higher yield, pressure must be increased to shift the equilibrium to the right.
  • However, pressure is expensive, and so this process is usually carried out at, or just above, atmospheric pressure.
• Conditions for contact process

  • Catalyst
  • Vanadium pentoxide catalyst
  • Does not change position of equilibrium
  • Increases the rate of reaction
• When designing an industrial process

  • Cost of raw materials
  • Availability of raw materials
  • Energy costs
  • Rate of reaction
  • Position of equilibrium