How is sulphuric acid manufacture by contact process ?

Explanation

Manufacture of sulphuric acid by contact process involves the following steps.
i. Initially sulphur dioxide is produced by burning sulphur or iron pyrites in oxygen/air.
`S+O_(2)rarrSO_(2)`
`4FeS_(2)+11O_(2)rarr2Fe_(2)O_(3)+8SO_(2)`
ii. Sulphur dioxide formed is oxidised to sulphur trioxide by air in the presence of a catalyst such as `V_(2)O_(5)` or platinised asbestos.
iii. The sulphur trioxide is absorbed in concentration sulphuric acid and produces oleum `(H_(2)S_(2)O_(7))`. The oleum is converted into sulphuric acid by diluting it with water.
`SO_(3)+H_(2)SO_(4)rarr H_(2)S_(2)O_(2)overset(H_(2)O)rarr 2H_(2)SO_(4)`
To maximise the yield the plant is operated at 2 bar pressure and 720 K. The sulphuric acid obtained is this process is over `96%` pure.