The Manufacture of sulphuric acid

• Sulphuric acid is produced using the Contact process
• In Zimbabwe there is a sulphuric acid production plant at Zimphos in Harare
• Sulpher or iron pyrites (iron sulphide) is roasted to form sulphur dioxide
• The word equation for roasting iron pyrites is:
• \text{iron sulphide+oxygen}\rightarrow\text{iron oxide+sulpher dioxide}
• The word equation for roasting sulpher is:
• \text{sulphur+oxygen}\rightarrow\text{sulpher dioxide}
• The sulphur dioxide is then mixed with excess air and then passed to a converter
• In the converter the mixture is converted into sulphuric acid by the Contact Process
• The sulphur dioxide is first converted into sulphur trioxide
• The reaction is reversible and exothermic
• \text{sulpher dioxide+oxygen}\xrightleftharpoons[catalyst]{450\degree C}\text{sulpher trioxide+heat}

The Contact Process

• Better yields are obtained at low temperatures
• However the reaction would be slow at low temperatures thus a catalyst is used
• Vanadium oxide is used as a catalyst
• A yield of 95% is obtained at 450°C and 1 atm pressure
• The sulpher trioxide is cooled and then absorbed into concerntrated sulphuric acid to oleum
• The gas is not dissolved in water as this would merely produce a sulphuric acid  mist due to the heat of the reaction
• The word equation for mixing sulphur trioxide and concerntrated sulphuric acid is:
• \text{sulphur trioxide+sulphur trioxide}\rightarrow\text{ oleum}
• The oleum is then mixed with either water or dilute sulphuric acid to form concentrated sulphuric acid
• \text{oleum+water}\rightarrow\text{concentrated sulphuric acid}

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