Condition required for better production sulphuric acid.
The above reaction is exothermic and proceeding with decrease in volume as 3 molecule on
reactant is producing only two molecules of product. Sulphur dioxide is oxidized to
Sulphur trioxide and it may decomposed back to Sulphur dioxide. According to Le-Chatelier
the following condition should be maintained :
1. Excess use of air or oxygen and Sulphur dioxide :
Air or oxygen should be used in excess amount along with Sulphur dioxide for greater
production of Sulphur trioxide.
2. Temperature
The reaction is exothermic. According to Le-chatelier principle low temperature is needed
to carry the reaction in forward direction. But if the temperature is very low then
the the rate of reaction will be slow and will not be productively advance. So, premature
of 400-450 C is maintained to proceed in forward direction and
without hampering the reaction.
3. Pressure :
The reaction is reversible and proceeding with decrease in volume. According to Le-chatelier priciple
high pressure is needed for this type of reaction but if the pressure is high then
the acid proof walls on the industry may burst due thigh pressure. Thus pressure of
2-3 is maintained.
4. Use of Catalyst
Looking at temperature and pressure the reaction may be slow so catalyst is used in the
reaction. Catalyst like divanadium pentaokide(V2O5) or platinum asbestos is used.
Platinum albestos is not used because is not cheap and is easily poisoned by arsenic
impurities mostly present in so2. Instead divanadium pentaoxide is used as it is cheap and doesn't poison.
5. Purity of Gases
All the gases used in the reaction should be in completely dry and pure state as any impurities present in the reacting gases act as catalytic poision and reduce the efficiency of catalyst.
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