sulphuric acid
source : SPM Chemistry form 4/form 5 Revision Notes
Manufacture of H2SO4 :
1) Lead chamber process :
principle:
SO2 is obtained by burning sulphur or iron pyrite (FeS2)
S + O2 —–> SO2
or
FeS2 (iron pyrite) + O2 —-> Fe2O3 + SO2
H2SO4 is obtained by the oxidation of SO2 in presence of NO catalyst.
SO2 + O2 + H2O ——-> H2SO4
Two mechanism has been subjected:
Berzelius mechanism :
2NO + O2 ——> 2NO2
NO2 + SO2 ——> SO3 + NO
SO3 + H2O —-> H2SO4
Navy and Lunge mechanism :
2NO + O2 —-> 2NO2
NO + NO2 + 2SO2 + O2 + H2O ——> 2(NO.HSO4) (Nitrosyl hydrogen sulphate)
2(NO.HSO4) + H2O —-> 2H2SO4 + NO +NO2
Process of manufacture of sulphuric acid :
source : sd senthil’s.Home page
1. Pyrite burner or sulphur burner:
It is a furnace in which sulphur or iron pyrite are burnt in presence of air to get SO2.
S+ O2 ——> SO2
or
4FeS2 + 11O2 —–> 2Fe2O3 + 8SO2
2. Dust chamber :
Mixture of impure SO2 and air obtained from pyrite burner is passed in dust chambers. Gaseous mixture comes in contact with steam then dust particles present in the mixture settle down in the bottom.
3. Nitre pot:
Mixture of SO2 and air obtained from dust chamber is passed in nitre pots. In this chamber oxide of nitrogen is obtained by heating NaNO3 and concentrated H2SO4.
NaNO3 + H2SO4 (concentrated) ——-> NaHSO4 + HNO3
4 HNO3 —–> 2H2O + NO2 + O2
4 HNO3 ——> 2H2O + 4NO + 3O2
Now oxide of nitrogen are prepared by passing ammonia and air over heated Platinum catalyst at 8000 C.
4NH3 + 5O2 —-> 4NO + 6H2O (at 800 0 C & Pt catalyst)
2NO + O2 ——-> 2NO2
4. Glover tower :
This tower is 3o feet in height and 8 feet in diameter. It is made of acid resistant bricks. It is packed with stone pieces . H2SO4 obtained from lead chamber and nitrosyl hydrogen sulphate obtained from Gay lussac tower dropped in glover tower. Mixture of SO2 , air and oxides of nitrogen obtained from nitre pots are passed in glover tower. Following reactions takes places:
a) Gaseous mixture is cooled to 50-80 0C
b) Some SO2 is oxidized to H2SO4
NO2 + SO2 + H2O ——-> H2SO4 + NO
c) Nitrosyl hydrogen sulphate obtained from gay lussac tower is hydrolyzed to sulphuric acid (H2SO4)
2 (NO.HSO4) + H2O —–> 2H2SO4 + NO + NO2
d) Dilute Sulphuric acid obtained from lead chamber is concentrated
5. Lead Chamber:
Mixture of SO2, air and oxide of nitrogen left in glover tower is sent to lead chamber these are made up of lead. Sulphuric acid does not react with lead. Stream is passed from the top. In this chamber dilute H2SO4 is obtained.
NO2 + SO2 + H2O ——> H2SO4 + NO
NO + O2 + SO2 + H2O ——-> H2SO4 + NO
6. Gay-lussac’s tower:
Unreacted gases obtained from lead chamber are passed in gay-lussac tower.H2SO4 is spread from the top then nitrosyl hydrogen sulphate is obtained which is taken back in glover tower.
NO + NO2 + 2H2SO4 ——> 2(NO.HSO4) + H2O
Purification of chamber acid :
Chamber acid contains impurity of lead sulphate , As2O3 and oxide of nitrogen. On diluting chamber acid lead sulphate precipitates put and is filters off. H2S is passed in the filtrate then yellow precipitate of arsenic tri sulphate are obtained which are filtered out.
As2O3 + 3H2S ——-> As2S3 (yellow precipitate) + 3H2O
filtrate is heated with ammonium sulphate which removes oxide of nitrogen in the form of nitrogen.
(NH4)2SO4 + NO + NO2 ——-> N2 + H2SO4 +H2O
