The Contact Process &

Making Sulphuric acidH2SO

4

Sulphuric Acid

H2SO4

• commercially important raw material

Sulphuric Acid

H2SO4

• commercially important raw material

Sulphuric Acid

H2SO4

• commercially important raw material

• more sulphuric acid made than any other compound

Sulphuric Acid

H2SO4

• commercially important raw material

• more sulphuric acid made than any other compound

• fertilisers, paints and pigments, detergents, car batteries, laboratory acid

Sulphuric Acid

H2SO4

• manufacturemanufacture

• propertiesproperties

• usesuses

Sulphuric Acid

H2SO4

• manufacturemanufacture

• propertiesproperties

• usesuses

H2O Air Sulphur

Sulphuric Acid

H2SO4

• manufacturemanufacture

H2O Air Sulphur

Step 1: Formation of SO2

either S + O2 SO2

or 2ZnS + 3O2 2SO2 + 2ZnO

Sulphuric Acid

H2SO4

• manufacturemanufacture

H2O Air Sulphur

Step 2: Formation of SO3 the Contact Process

2SO2 + O2 2SO3 ΔH = -197 kJ

mol – 1

exothermic

Sulphuric Acid

H2SO4

• manufacturemanufacture

H2O Air Sulphur

Step 3: Formation of Oleum

SO3 + conc H2SO4 H2S2O7

[the direct combination of SO3 with water is too exothermic and forms a fine mist of acid]

Sulphuric Acid

H2SO4

• manufacturemanufacture

H2O Air Sulphur

Step 4: Dilution of Oleum

H2O + H2S2O7 2H2SO4

the oleum is diluted to give the desired concentration of sulphuric acid

Sulphuric Acid

H2SO4

• manufacturemanufacture

H2O Air Sulphur

Step 2: Formation of SO3 the Contact Process

2SO2 + O2 2SO3

exothermicLet’s look at this equilibrium more closely….

Sulphuric Acid

Step 2: Formation of SO3 the Contact Process

Factors:• CatalystCatalyst

• TemperatureTemperature

• PressurePressure

2SO2 + O2 2SO3

exothermic

Sulphuric Acid

Step 2: Formation of SO3 the Contact Process

2SO2 + O2 2SO3

exothermic

Factors:• Catalyst Catalyst VV22OO55

• TemperatureTemperature

• PressurePressure

Sulphuric Acid

Step 2: Formation of SO3 the Contact Process

2SO2 + O2 2SO3

exothermic

Factors:• Catalyst Catalyst VV22OO55

• Temperature Temperature 450450ooCC

• PressurePressure

Sulphuric Acid

Step 2: Formation of SO3 the Contact Process

2SO2 + O2 2SO3

exothermic

Factors:• Catalyst Catalyst VV22OO55

• Temperature Temperature 450450ooCC

• Pressure Pressure 1-2 atmospheres1-2 atmospheres

***These are compromise conditions***

Sulphuric Acid

Step 2: Formation of SO3 the Contact Process

2SO2 + O2 2SO3

exothermic

Factors:• Catalyst Catalyst VV22OO55

***These are compromise conditions***

• The catalyst works best as the temperature increases• Provides an alternative path with a lower Eact

• Speeds up time taken to achieve equilibrium• Several catalyst beds used to achieve high yield

Sulphuric Acid

Step 2: Formation of SO3 the Contact Process

2SO2 + O2 2SO3

exothermic

Factors:• Temperature Temperature 450450ooCC

***These are compromise conditions***

• The yield of SO3 increases as T is decreasedHowever •Catalyst does not work if T is too low• Rate of attainment of equilibrium is slow if T is too low

Sulphuric Acid

Step 2: Formation of SO3 the Contact Process

2SO2 + O2 2SO3

exothermic

Factors:• Pressure Pressure 1-2 atmospheres1-2 atmospheres

***These are compromise conditions***

• The yield of SO3 increases as P is increased• High pressure is costly £££

Sulphuric Acid

H2SO4

• manufacturemanufacture

• propertiesproperties

• usesuses

Sulphuric Acid

H2SO4

• manufacturemanufacture

• propertiesproperties

• usesuses

Dehydrating agent

Viscous liquid

Sulphuric Acid

H2SO4

• manufacturemanufacture

• propertiesproperties

• usesuses

Dehydrating agent

Viscous liquidViscous liquid

Conc H2SO4 will dehydrate hydrated copper sulphateand carbohydrates (e.g. sugar)