How nitric acid is made
Nitric acid is made by burning ammonia on a screen of platinum wire, the way it has been since 1902.
- stations
- 5
- things upstream
- 4
- raw sources
- 3
- steps from the ground
- 2
The short version
Nitric acid is made from ammonia. Ammonia gas is mixed with air and burned over a fine mesh of platinum and rhodium, forming nitric oxide. The gas is cooled so it reacts further with oxygen, then it is absorbed in water to make dilute nitric acid, which is distilled to a higher strength.
-
Mix ammonia with air
Ammonia gas is vaporized and blended with filtered air in carefully controlled proportions. That blend is the fuel for the entire process.
-
Burn it over platinum gauze
The mixture flows through several layers of fine platinum and rhodium wire mesh and burns in a fraction of a second, giving nitric oxide and steam. The burn gives off plenty of heat, so once it has started it keeps itself going.
-
Cool and oxidize the gas
Heat exchangers cool the gas, recovering the heat as steam. As it cools, nitric oxide picks up more oxygen from the air and turns into brown nitrogen dioxide.
-
Absorb it in water
The brown gas rises through a column of plates while water trickles down. It dissolves into dilute nitric acid, and some of the gas that is left over turns back into nitric oxide and goes round again.
Goes in -
Concentrate by distilling
The weak acid is distilled to the strength a buyer needs. Most of it goes straight on to make fertilizer.
Worth repeating
- The platinum catalyst slowly degrades into a cauliflower-like texture in the furnace, and plants swap the gauze out regularly.
- Wilhelm Ostwald patented the method in 1902, but it became economical only after the Haber-Bosch process began supplying ammonia.
- Germany kept making nitric acid during the First World War, when the Allied blockade cut off imports of Chilean nitrate, because it could make ammonia from air.
Back to the ground
Follow every input upstream and nitric acid starts as these 3 raw sources.
Where it goes next
Nitric acid feeds 7 lines directly and reaches 179 things in total.
Further down the line
Keep walking
Sources
Cite this page: "How nitric acid is made." Assembly Line, 2026-11-03. https://assemblyline.org/make/nitric-acid