Making Ammonia - the Harber Process

Making ammonia - The Haber process

During the last century, the populations of Europe and America rose very rapidly. More food and more
crops were needed to feed more and more people. So farmers began to use nitrogen compounds as
fertilisers. The main source of nitrogen compounds for fertilisers was sodium nitrate from Chile. By
1900 supplies of this were running out. Another supply of nitrogen had to be found or many people
would starve. The obvious source of nitrogen was the air (about 78% of the air is nitrogen).
Unfortunately, nitrogen is not very reactive. This made it difficult to convert it into ammonium salts and nitrates for use as fertilisers. A German chemist called Fritz Haber solved the problem.

In 1904, Haber began studying the reaction between nitrogen and hydrogen. By 1908 he had found the
conditions needed to make ammonia (NH3). Eventually, the Haber process became the most important
method of manufacturing ammonia.

The raw materials for the Haber process are Natural gas, air and water. In the first stage, Natural gas
(which is mostly methane) is reacted with steam to produce carbon dioxide and hydrogen. To speed up
the reaction, a catalyst is used. A high temperature and a high pressure also speeds up the reaction.
In the second stage, some of the hydrogen from the first stage is burnt in air. The oxygen in the air reacts with the hydrogen to make steam. The reason for this second stage is to remove the oxygen from the air to leave nitrogen behind. It also makes a lot of the heat needed in the Haber process.
In the third stage, hydrogen from the first stage is mixed with nitrogen from the second stage. The two
gases are put under high temperature and high pressure. Usually 400°C and 150–300 atmospheres of
pressure are used. Iron is also added as a catalyst. Some of the gases are converted to ammonia. The
ammonia is cooled to turn it into a liquid. The liquid ammonia is then run off from the gases. The
unconverted gases...