How ammonia is made
Ammonia plants make fertilizer out of air and natural gas, and that feeds about half the people alive.
- stations
- 6
- things upstream
- 3
- raw sources
- 3
- step from the ground
- 1
The short version
Ammonia is made by combining nitrogen from the air with hydrogen from natural gas over an iron catalyst at high pressure and heat. Only a fraction of the gas reacts on each pass. The ammonia is chilled into a liquid and drained off, and the unreacted gas is sent around the loop again.
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Make hydrogen from gas
Natural gas is cleaned and reacted with steam over a nickel catalyst, which strips out hydrogen and leaves carbon dioxide as a byproduct. Plants in some regions use coal for this step instead.
Goes in -
Take nitrogen from air
Air is added in a second reactor where its oxygen is burned away, which leaves nitrogen mixed into the hydrogen stream. Air is about 78% nitrogen, but that nitrogen is so stable that it takes a catalyst and high pressure to make it react.
Goes in -
Scrub out the carbon dioxide
Carbon dioxide and traces of other gases are washed out of the mixture, because they would poison the catalyst. The carbon dioxide is often sold to urea and beverage plants.
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Compress the gas mix
Multistage compressors squeeze the clean hydrogen and nitrogen to a very high pressure. The compressors are among the biggest machines in the plant.
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Pass it over the iron catalyst
The hot, pressurized gas flows through beds of iron catalyst. Only about 15% of it turns into ammonia on each pass.
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Chill out the liquid
Refrigeration condenses the ammonia into a liquid that is drained off and stored. The gas that did not react goes back to the compressor, and after many laps nearly all of it ends up as ammonia.
Worth repeating
- Making ammonia uses roughly 1 to 2% of the world's energy and causes about 3% of global carbon dioxide emissions.
- The first industrial ammonia plant opened in 1913 at Oppau in Germany, after Fritz Haber's lab success and Carl Bosch's scale-up at BASF.
- The iron catalyst still used today was found by BASF researcher Alwin Mittasch, who tested it as a cheaper alternative to rarer metals.
Back to the ground
Follow every input upstream and ammonia starts as these 3 raw sources.
Open the whole family tree
Where it goes next
Ammonia feeds 17 lines directly and reaches 346 things in total.
Further down the line
Keep walking
Sources
Cite this page: "How ammonia is made." Assembly Line, 2026-11-03. https://assemblyline.org/make/ammonia