Describe the priciple of manfacture of sulphuric acid by contact process. What are the limitations of this process and how are these overcome?
The Contact Process is a process involving the catalytic oxidation of sulfur dioxide, SO2, to sulfur trioxide, SO3.
S(s) + O2(g) → SO2(g)
2SO2(g) + O2(g) → 2SO3(g)
Any unreacted gases from the above reaction are recylced back into the above reaction
The activation energy of the oxidation reaction of sulfur oxide with oxygen to sulfur oxide is very high. Therefore, in the absence of a catalyst, the oxidation reaction does not proceed even at high temperatures. The use of a catalyst reduces the activation energy of the reaction and increases the rate of oxidation.
This stage is considered to be limiting in the process of production of sulfuric acid, since its implementation is not possible without the use of expensive catalysts that lose their usefulness due to oxidation and are an unstoppable resource.
SO3(g) + H2SO4 → H2S2O7
This is done because when water is added directly to sulfur trioxide to produce sulfuric acid
SO3(g) + H2O(l) → H2SO4(l)
the reaction is slow and tends to form a mist in which the particles refuse to coalesce.
H2S2O7(l) + H2O(l) → 2H2SO4(l)