Preparation of Sulphuric Acid by Contact process

Sulphuric acid - Contact Process

We will first start by addressing the question of what is sulphuric acid. Well, sulphuric acid is basically an oxidizing agent, a strong mineral acid, and a dehydrating agent. Sulphuric acid has the chemical formula H2SO4.

The acid is a colorless liquid. It is soluble in water and generally releases heat on contact. Further, the acid is corrosive in nature to metals and tissues. It will even char wood and most other organic matter on contact, but chances of objects catching fire are null. The acid has a density of 15 lb/gal. Exposure to the acid can result in adverse health effects from inhalation. It depends on the rate of exposure and concentration.

Sulfuric Acid Structure - Contact Process

Sulfuric Acid 3D ball Structure

That being said, the acid is usually manufactured using a method known as the contact process. Earlier, in this process, a chemical element known as platinum was first used as a catalyst. Later, an inorganic compound known as vanadium oxide replaced platinum due to cost constraints.

In any case, today we will be looking at contact process in detail.

Contact process for manufacturing of sulphuric acid:

Steps involved in the manufacturing of sulphuric acid are as stated below:

  1. Preparation of sulphur dioxide.
  2. Conversion of sulphur dioxide into sulfur trioxide.
  3. Conversion of sulfur trioxide formed into concentrated H2SO4.

Sulphuric acid - Contact Process

Step 1: Preparation of sulphur dioxide:

SO2 is prepared by burning sulphur in the presence of excess air so that the product combines with oxygen which is helpful for the next stage.

S(s) + O2 (g) → SO2(g)

Step 2: Preparation of sulphur trioxide:

Sulphur trioxide is formed when sulphur dioxide reacts with oxygen in a ratio of 1:1 at a temperature of 400°C – 450°C and a pressure of 1-2 atm in the presence of N2O5 as a catalyst. This reaction is reversible in nature.

2SO2(g) + O2(g) ⇌ 2SO3(g)

Step 3: Preparation of concentrated sulphuric acid:

The sulphur trioxide formed is first made to react with concentrated sulphuric acid. Sulphur trioxide cannot be dissolved in water directly as it leads to the formation of fog. The product obtained after this reaction is known as oleum. The oleum obtained is then dissolved in water to obtain concentrated sulphuric acid.

H2SO4 + SO3(g) → H2S2O7(l)

H2S2O7(l) + H2O(l) → 2H2SO4

Uses of sulphuric acid

In Industries:

  • Up to 50 percent of this liquid manufactured is used in the production of phosphoric acid which is in turn used to make phosphate fertilizers.
  • It is used in the manufacturing of metals such as copper, zinc etc.
  • 5 percent of the produced acid is used in the making of fibers.

In Domestic Environments:

  • Used in acidic drain cleaners.
  • Due to its strong dehydrating property, it can be used to remove tissue paper.

As a Catalyst:

  • Used as a catalyst in the manufacturing process of nylon.
  • Used in the Manheim process in the manufacturing of HCl.
  • Used in petroleum refining.

For a detailed discussion on preparation and uses of sulphuric acid, download Byju’s – the learning app.

Practise This Question

Which process is used to separate a soluble solid from a solution?