CHAPTER 5. THE CHEMICAL INDUSTRY 5.4
(a) HABER PROCESS
The production of ammonia
from nitrogen and hydrogen
(b) OSTWALD PROCESS
Production of nitric acid
from ammonia and oxygen
(c) NITROPHOSPHATEPROCESS
Acidification of phosphate rock
with nitric acid to produce phosphoric
acid and calcium nitrate
Figure 5.9: Flow diagramshowing steps in the production of nitrogen fertilisers
a hydrocarbon such as methane reacts with waterto form carbon monoxide
and hydrogen accordingto the following equation:
CH 4 + H 2 O→ CO + 3H 2
Nitrogen and hydrogenare then used in the Haber process. The equation
for the Haber process is:
N 2 (g) + 3H 2 (g)→ 2NH 3 (g)
(The reaction takes place in the presence of an iron (Fe) catalyst under con-
ditions of 200 atmospheres (atm) and 450 − 500 C)
FACT
The Haber process de-
veloped in the early 20th
century, before the start
of World War 1. Be-
fore this, other sources
of nitrogen for fertilisers
had included saltpeter
(NaNO 3 ) from Chile and
guano. Guano is the
droppings of seabirds,
bats and seals. By the
20th century, a number
of methods had been de-
veloped to ’fix’ atmo-
spheric nitrogen. One
of these was the Haber
process, and it advanced
through the work of
two German men, Fritz
Haber and Karl Bosch.
They worked out what
the best conditions were
in order to get a high
yield of ammonia, and
found these to be high
temperature and high
pressure. During World
War 1, the ammonia that
was produced through
the Haber process was
used to make explosives.
(b) The Ostwald Process
The Ostwald process isused to produce nitric acid from ammonia. Nitric
acid can then be usedin reactions that produce fertilisers. Ammoniais
converted to nitric acidin two stages. First, it is oxidised by heating with
oxygen in the presence of a platinum catalyst to form nitric oxide and water.
This step is strongly exothermic, making it a useful heat source.
4NH 3 (g) + 5O 2 (g)→ 4NO(g) + 6H 2 O(g)
Stage two, which combines two reaction steps, iscarried out in the presence
of water. Initially nitric oxide is oxidised again toyield nitrogen dioxide:
2NO(g) + O 2 (g)→ 2NO 2 (g)
This gas is then absorbed by the water to produce nitric acid. Nitric oxide
is also a product of thisreaction. The nitric oxide (NO) is recycled, andthe
acid is concentrated to the required strength.
3NO 2 (g) + H 2 O(l)→ 2HNO 3 (aq) + NO(g)
(c) The Nitrophosphate Process
The nitrophosphate process involves acidifyingphosphate rock with nitric
acid to produce a mixture of phosphoric acid and calcium nitrate:
Ca 3 (PO 4 ) 2 + 6HNO 3 + 12H 2 O→ 2H 3 PO 4 + 3Ca(NO 3 ) 2 + 12H 2 O
When calcium nitrate and phosphoric acid react with ammonia, a com-
pound fertiliser is produced.
