Contact Process | Chemistry for Grade 11 (IGCSE) PDF Download

The Contact Process

• Sulfuric acid is produced using the Contact process.
• Concentrated sulfuric acid finds applications in car batteries, the production of fertilizers, soaps, and detergents.
• The initial step involves generating sulfur dioxide, achieved through burning sulfur to oxidize it or by roasting sulfide ores.
  S + O₂ → SO₂
• The pivotal step in the Contact process entails oxidizing sulfur dioxide into sulfur trioxide with the aid of a vanadium(V) oxide catalyst, V₂O₅.
  2SO₂ + O₂ ⇄ 2SO₃
• The oxygen required for this stage is sourced from the air.
• The key conditions for this main production stage are:
  • A temperature of 450°C
  • A pressure of 2 atm (200 kPa)
• Once sulfur trioxide is created, it progresses through additional processes to yield sulfuric acid.

Explaining the Conditions in the Contact Process

Similar to the Haber process, the pressure and temperature parameters are crucial in the Contact process.

The main stage of the Contact process is represented by an equation:
2SO₂ + O₂  ⇄  2SO₃

Temperature: 450°C

• Since the forward reaction is exothermic, raising the temperature causes the equilibrium to shift towards the left, favoring the formation of reactants.
• Consequently, elevating the temperature reduces the yield of sulfur trioxide.
• Determining the optimal temperature involves balancing the benefits of a faster reaction rate at higher temperatures with the drawback of lower equilibrium yield.

Pressure: 2 atm

• When pressure increases, the equilibrium in the Contact Process shifts towards the right, favoring the formation of a smaller number of gaseous molecules.
• At high pressures, the position of equilibrium heavily favors the production of sulfur trioxide, with the mixture containing approximately 96% sulfur trioxide.
• Reasons for Operating at Slightly Above Atmospheric Pressure
  • High pressures in the process can pose serious safety risks and require expensive equipment to handle.
  • The increase in pressure leads to the liquefaction of sulfur dioxide, which is undesirable.