Pure ammonia—often called anhydrous ammonia—serves as a cornerstone in agriculture, industry, and research. Unlike household ammonia, which is a dilute aqueous solution, anhydrous ammonia is a dense, high‑purity compound produced on a commercial scale from natural gas, air, and steam. The following steps outline the established, large‑scale process that delivers liquid ammonia at industrial quality.
Natural gas is first passed through a hydrogen‑rich stream that reacts with sulfur compounds to form hydrogen sulfide (H₂S). The H₂S is then scrubbed with zinc oxide beds, converting it to zinc sulfide (ZnS) and water. The resulting gas stream is now largely methane (CH₄) with minimal sulfur contamination.
The purified methane is heated to approximately 1,500 °F (≈820 °C) in the presence of steam and a ferric oxide catalyst. This steam reforming reaction produces a mixture of carbon monoxide (CO), hydrogen (H₂), and a small amount of water vapor:
CH₄ + H₂O → CO + 3 H₂
Subsequent water–gas shift reactions convert the CO to carbon dioxide (CO₂) and additional H₂:
CO + H₂O → CO₂ + H₂
CO₂ and any residual CO are removed using absorbents such as ethanolamine solutions. The purified stream is then treated with excess hydrogen to drive the equilibrium toward methane and water, yielding a high‑purity H₂ gas stream.
Exactly one mole of nitrogen (N₂) is introduced for every three moles of hydrogen, and the mixture is subjected to a ferric oxide catalyst under high pressure (typically 150–300 bar). The catalytic reaction proceeds as:
3 H₂ + N₂ → 2 NH₃
The freshly formed ammonia gas is cooled to –30 °F (≈–34 °C) while maintaining pressure, condensing it into a dense liquid. This liquid is then stored in insulated, pressure‑rated tanks for distribution.
Throughout the process, rigorous safety protocols are essential due to the handling of high‑temperature gases, high‑pressure vessels, and flammable hydrogen. Environmental controls, such as sulfur capture and CO₂ sequestration, are also integral to sustainable ammonia production.
