The Haber process
is not the only catalytic reaction involved in modern ammonia production,
and improved chemical engineering of all the steps has led to a
big reduction in the energy needed to produce ammonia.
Energy Cost of Ammonia Production
The feedstock
today in the UK is natural gas, air and steam. Several steps are
needed, using a range of different catalysts. The separate processes
are listed.
Purification of natural gas to remove
sulphur compounds
Reaction of methane and steam
CH4(g) + H2O(g)
CO(g) + 3H2(g)
and unreacted CH4
Oxygen from the air reacts with some
of the hydrogen
2H2(g) + O2(g)
2H2O(g)
The resulting steam and heat converts most of the remaining
methane
CH4(g) + H2O(g)
CO(g) + 3H2(g)
Removal of carbon monoxide by mixing
gases with steam
CO(g) + H2O(g)
CO2(g)
+H2(g)
Removal of CO2
by reaction with a base, followed by removal of last traces
of CO and CO2 by reaction with H2
to give methane and steam.
The gas mixture entering the ammonia
reactor is 74 % hydrogen, 25 % nitrogen, 1 % methane
N2(g)
+ 3H2(g)
2NH3(g)
A balanced equation for the overall process
is
7CH4 +
8N2 + 2O2 + 10H2O
7CO2 + 16NH3
The whole operation is integrated and continuous.
Other than ammonia the only outputs are waste heat, and carbon
dioxide. The carbon dioxide can be collected and sold.
Question
Why is this necessary?
Answer
Sulphur is a catalyst poison
Catalyst: cobalt and nickel oxides on alumina
support
Catalyst: nickel oxide on calcium aluminate
support
Catalyst: iron oxide
Catalyst: nickel
Catalyst: promoted iron
Catalyst: nickel
Question
If you were looking for a new catalyst
to do better than iron what metals would you consider?
CO(g) + 3H2(g)
