Answer to Question #87793 in Inorganic Chemistry for Rahul bisht

Question

Describe the priciple of manfacture of sulphuric acid by contact process. What are the limitations of this process and how are these overcome?

Answer 1

Describe the priciple of manfacture of sulphuric acid by contact process. What are the limitations of this process and how are these overcome? 

Answer:

The Contact Process is a process involving the catalytic oxidation of sulfur dioxide, SO₂, to sulfur trioxide, SO₃.

1. Solid sulfur, S(s), is burned in air to form sulfur dioxide gas, SO₂

S(s) + O₂(g) → SO₂(g)

1. The gases are mixed with more air then cleaned by electrostatic precipitation to remove any particulate matter
2. The mixture of sulfur dioxide and air is heated to 450^oC and subjected to a pressure of 101.3 - 202.6 kPa (1 -2 atmospheres) in the presence of a vanadium catalyst (vanadium (V) oxide) to produce sulfur trioxide, SO₃(g), with a yield of 98%.

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.

1. Sulfur trioxide, SO₃(g) is dissolved in 98% (18 M) sulfuric acid, H₂SO₄, to produce disulfuric acid or pyrosulfuric acid, also known as fuming sulfuric acid or oleum, H₂S₂O₇.

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.

1. Water is added to the disulfuric acid, H₂S₂O₇, to produce sulfuric acid, H₂SO₄

H₂S₂O₇(l) + H₂O(l) → 2H₂SO₄(l)