Sulphuric Acid…

Prepared By:Marium Farooq

SOx refers to all sulphur oxides, the two major ones being sulphur dioxide (SO2) and sulphur trioxide (SO3).

Introduction

• Sulphur dioxide is a colourless gas with a pungent, irritating odour and taste. It can be obtained by the combustion of sulphur in air.

It is highly soluble in water forming weakly acidic sulphurous acid.

S (s) + O2 (g) SO2 (g)

SO2 (g) + H2O (l) H2SO3 (l)

Sulphur dioxide or sulphur (IV) oxide

Natural sources of sulphur dioxide include:

• volcanoes and hot springs.

• the oxidation of hydrogen sulphide (H2S), a toxic gas that smells like rotten eggs.

Man-made sources of sulphur dioxide include:

• coal combustion, ore refining, chemical manufacturing and other fossil fuel processing and burning.

Sources of Sulphur dioxide

• Sulphur dioxide is used in many industrial processes such as :

• In the Manufacture of sulphuric acid.

• As a food preservative.

• As a steriliser

• As a bleach in the manufacturing of wood pulp.

Uses of Sulphur dioxide

• When sulphur dioxide combines with the oxygen (O2) in the air some sulphur trioxide is slowly formed.

• Sulphur trioxide rapidly combines with water to produce sulphuric acid. This reaction is extremely violent.

Sulphur trioxide or sulphur (VI) oxide

2SO2 (g) + O2 (g) 2SO3 (g)

SO3 (g) + H2O (l) H2SO4 (l)

The Industrial Manufacture of Sulphuric Acid

The Contact process

Almost all sulfuric acid in the world today is made by the Contact Process, first patented in 1831 and so called because in a key step, the reactants are in contact with the catalyst, vanadium pentoxide V2O5

The Industrial Manufacture of Sulphuric Acid

The Contact process

  

This reaction is exothermic and the heat given out is used to   (a) maintain the temperature of the process   (b) generate electricity to run the plant.

Step 1     burning sulfur in air to form sulfur dioxide     

S  +  O2  →  SO2

Step 2  oxidising the sulfur dioxide to sulfur trioxide.  2SO2  +  O2  →  2SO3 (ΔH = −196 kJ·mol−1)

 

The reaction is slow and the V2O5 catalyst speeds up the rate of reaction, at a moderate temperature of about 450oC. Extra oxygen and a slight increase in pressure (2-3 atm) are used to ensure a high conversion. 

Step 3  The sulfur trioxide is dissolved in concentrated sulfuric acid to form another acid called oleum., H2S2O7 Oleum means 'oil-like‘

SO3  +  H2SO4  →  H2S2O7

 

Step 4  The Oleum is then diluted with water to the required strength of acid.

 H2S2O7  +  H2O  →  2H2SO4

 

why water is not used to dissolve the sulfur trioxide

directly to form sulfuric acid ??

because sulfur trioxide would react with the water vapour above the water forming a fine mist of sulfuric acid. This is a potential hazard and so absorptioninto concentrated sulfuric acid is preferred.

Sulphuric acid, H2SO4 is the largest volume industrial chemical produced in the world. The consumption of sulfuric acid is often used to monitor a country's degree of industrialisation.

Sulphuric Acid…

• It is a viscous, high density liquid, known in antiquity as oil of vitriol.

• It is sold as 98% (concentrated), 10% (dilute) or 29-32% in car batteries.

Uses Of Sulphuric Acid…

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