Page 265 - Chemistry ICSE Class X

Study of Compounds–Sulphuric Acid 251
Manufacture of Sulphuric Acid

Two processes employed for the manufacture of sulphuric acid are
/ŶĚŝĂ ƉƌŽĚƵĐĞƐ ĂďŽƵƚ ϭϱϬ ŵŝůůŝŽŶ
ƒ Lead chamber process ƚŽŶŶĞƐ ŽĨ ƐƵůƉŚƵƌŝĐ ĂĐŝĚ ĂŶŶƵĂůůLJ͘
ƒ Contact process
Nowadays, the Contact process is widely used for the manufacture of
sulphuric acid.

How is sulphuric acid manufactured by Contact process
In Contact process, sulphur dioxide is oxidised to sulphur trioxide by air in
the presence of catalyst vanadium pentoxide. Sulphur trioxide so produced
is absorbed in conc. H SO to produce oleum (H S O ). Oleum is then
4
7
2
2 2
reacted with a calculated amount of water to form H SO of the desired
2
4
concentration.
The chemistry involved in the contact process is described below.
ƒ Production of SO . SO is obtained by burning sulphur or iron pyrites. John Roebuck
2
2
burn
S(s) + O (g) o SO (g) ;ϭϳϭϴ Ͳ ϭϳϵϰͿ
2
2
sulphur from air sulphur dioxide ,Ğ ĚĞǀĞůŽƉĞĚ >ĞĂĚ ŚĂŵďĞƌ
WƌŽĐĞƐƐ ĨŽƌ ůĂƌŐĞ ƐĐĂůĞ ƉƌŽĚƵĐƟŽŶ ŽĨ
burn
4FeS (s) + 11O (g) o Fe O (s) + 8SO (g) ƐƵůƉŚƵƌŝĐ ĂĐŝĚ͘
2
2
3
2
2
iron pyrites from air sulphur
dioxide &ĂǀŽƵƌĂďůĞ ĐŽŶĚŝƟŽŶƐ ĨŽƌ ƚŚĞ
ŽdžŝĚĂƟŽŶ ŽĨ ^K ƚŽ ^K ŝŶ ƚŚĞ
2
3
ƒ Catalytic oxidation of SO to SO . Sulphur dioxide is oxidised by air ŽŶƚĂĐƚ ƉƌŽĐĞƐƐ ĂƌĞ͕
2
3
in the presence of vanadium pentoxide (V O ) catalyst to give sulphur ͻഩ >Žǁ ƚĞŵƉĞƌĂƚƵƌĞ͘ KƉƟŵƵŵ
5
2
trioxide. ƚĞŵƉĞƌĂƚƵƌĞ ŝƐ ϰϱϬΣ ;с ϳϮϯ <Ϳ
2 atm, 723 K
2SO (g) + O (g) o 2SO (g) ͻഩ ,ŝŐŚ ƉƌĞƐƐƵƌĞ͘ ^ŝŶĐĞ ŚŝŐŚ ƉƌĞƐƐƵƌĞ
3
2
2
2
5
sulphur dioxide (in excess) V O catalyst sulphur trioxide ƚŽǁĞƌƐ ĂƌĞ ŶŽƚ ĞĂƐLJ ƚŽ ďƵŝůƚ͕
ŚĞŶĐĞ Ă ƉƌĞƐƐƵƌĞ ŽĨ ĂďŽƵƚ Ϯ Ăƚŵ ŝƐ
ƒ Conversion of sulphur trioxide to oleum. Sulphur trioxide is ĐŽŶƐŝĚĞƌĞĚ ŽƉƟŵƵŵ͘
dissolved in concentrated sulphuric acid to produce oleum or fuming ͻ džĐĞƐƐ ŽĨ ŽdžLJŐĞŶ͘ dŽ ƐŚŝŌ ƚŚĞ
sulphuric acid. ƌĞĂĐƟŽŶŝŶƚŚĞ ĨŽƌǁĂƌĚĚŝƌĞĐƟŽŶ͕
ĞdžĐĞƐƐ ŽĨ ŽdžLJŐĞŶ ŝƐ ŶĞĞĚĞĚ ƚŽ
SO (g) + H SO (l) o H S O (l) ĐŽŶǀĞƌƚ ĂůŵŽƐƚ ƚŚĞ ǁŚŽůĞ ŽĨ ^K
7
2
4
3
2 2
sulphur trioxide conc. oleum ƚŽ ^K ͘ 2
3
ƒ Conversion of oleum to sulphuric acid. Oleum is diluted with ͻ ƐƵŝƚĂďůĞ ĐĂƚĂůLJƐƚ͘ WůĂƟŶƵŵ ŝƐ Ă
a calculated amount of water to get sulphuric acid of the desired ŐŽŽĚ ĐĂƚĂůLJƐƚ͕ ďƵƚ ĚƵĞ ƚŽ ŝƚƐ ŚŝŐŚ
concentration. ĐŽƐƚ ĂŶĚ ƚĞŶĚĞŶĐLJ ƚŽ ŐĞƚ ƉŽŝƐŽŶĞĚ
ĞĂƐŝůLJ͕ ǀĂŶĂĚŝƵŵ ƉĞŶƚŽdžŝĚĞ
H S O (l) + H O(l) o 2H SO (aq) (V O ͿŝƐƵƐĞĚĂƐĂĐĂƚĂůLJƐƚ ĨŽƌƚŚĞ
2 2
4
2
2
7
2 ϱ
oleum water sulphuric acid ŽdžŝĚĂƟŽŶ ŽĨ ^K ƚŽ ^K ͘
2
3
(calculated amount)
The contact process plant is shown in Fig. 11.1.
Fig. 11.1 The Contact process for the manufacture of sulphuric acid