Industrial Catalysis

Ammonia synthesis

There are three main stages in the manufacture of ammonia. The Haber process is the third stage and uses a catalyst.

Summary of conditions and catalyst for the Haber process

world annual production 140 million tonnes

gas mixture

75% hydrogen, 25% nitrogen

pressure

150 atmospheres

temperature

650 - 720 K

catalyst

iron

conversion up to 98% (15% per pass)
   
Major uses of ammonia

 

The three main stages in ammonia synthesis

a)

conversion of methane and steam to hydrogen and carbon monoxide

 

This process is called steam reforming and we will look at it in detail in the next section.

b)

removal of the carbon monoxide and the production of a mixture of hydrogen and nitrogen

 

This is called the shift reaction.

c)

synthesis of ammonia in the Haber process

 

N2 + 3H2

2NH3

DH = -92 kJmol-1

 

 

 

 

More on the Haber process

Catalyst: iron, with potassium hydroxide as a promoter in a series of beds, with cooling between beds.

Ammonia removal: ammonia is condensed out of the gas stream by refrigeration and unchanged reactant is replenished and re-circulated.

Conversion: about 15% ammonia is produced per pass, but by re-circulating the gases yields of up to 98% are achieved.