The contact process is the industrial method used for producing large amounts of sulphuric acid.

The first stage is to convert sulphur to sulphur dioxide by reacting it with oxygen:

S + O2 → SO2

Then, more oxygen is added to turn it to sulphur trioxide:

2SO2 + O2 ⇌ 2SO3

In order to receive to maximum reaction rate with this reversible reaction, certain conditions are required:

  • 450°C
  • 1-2 atm
  • Vanadium Penta-oxide (V2O5) catalyst. (Platinum would be more effective, but it is very expensive)

The sulphur trioxide is then reacted with sulphuric acid to produce oleum:

SO3 + H2SO4 → H2S2O7

The oleum is then reacted with water to produce concentrated sulphuric acid:

H2S2O7 + H2O → 2H2SO4

(The sulphur trioxide is not directly added to water because the reaction would be too violent)


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