Describe the industrial manufacture of Sulphuric Acid by Contact Process with a balanced chemical equation. | web4study

Describe the industrial manufacture of Sulphuric Acid by Contact Process with a balanced chemical equation.


This method was developed in Germany in the early 19th century but came into operation from 1912. Nowadays sulphuric acid is mostly manufactured by the contact process.

In Pakisrm sulphuric acid is also manufactured by this process and hence contact method is described here.

In this method 502 is produced mainly by burning sulphur In dry air or iron pyrite in pyrite burners.

It is very important that in contact process 502 and air must be very pure, free from all sons of impurities which poison the catalyst; so the mixture of 502 and air is passed through special dust filters. The solid particles settle down in the dust chamber. Then S02 _is passed through the washing or scrubbing chamber. Here steam is injected from the top of the chamber. Solid particles from droplets with steam and settle down. The moist mixture of SO and the air is passed through the drying towers in which cone. HzS04 is sprayed from the top.

This washed, a dried and purified mixture of S02 and air is passed through contact tower i.e. Catalytic chamber. In this tower, SO2 is oxidized to 503 in the presence of catalyst vanadium pentaoxide (V2O5} or PL The catalyst arranged in contact tower in such a way that it exposes the maximum possible surface area, for the reacting gaseous mixture. Since Pt is very expensive, so it is replaced by finely divided, V205 which is less expensive and more resistant to impurities. The reaction occurs as:

Since the reaction is reversible and exothermic, the favourable conditions for obtaining the maximum yield of S03 are (a) low temperature (b) high pressure (c) excess of 0 2″

In actual practice the optimum. the temperature chosen in the presence of a catalyst is 450°C; whil~ the optimum pressure should be the 1.5-1.7 atmosphere.

The sulphur trioxide (503) produced in a contact tower is not directly dissolved in water; because it is less soluble in it. Therefore, S03 . is absorbed first in 97% cone. sulphuric acid producing a very thick liquid called Oleum i.e. Pyrosulphuric acid in the absorption tower.

Oleum is then diluted With appropriate amount of water to get sulphuric acid of desired concentration.

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