Haber-Bosch Process

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Overview

The Haber-Bosch process is the globally dominant production method for producing ammonia. It works by reacting nitrogen from the air with hydrogen under very high pressure (200 to 400 bar) and moderately high heat (400° to 650° C / 750° to 1200° F). An iron-based catalyst is used to allow the reaction to proceed at a lower temperature. Generally speaking, in catalytic chemical reactions, the catalyst itself is not consumed in the reaction and can be recycled and re-used many times. As ammonia forms, it is continuously removed, keeping the reaction in a constantly stable state for production. Typically, lower temperatures and higher pressures increase the overall yield of ammonia.

Source: Haber-Bosch Process Diagram, Science Notes, 2025.

How is the hydrogen produced?

The most common and cost-effective way to make hydrogen from syngas produced via the Steam Methane Reforming process. In this method, natural gas (mainly methane) reacts with steam at high pressure (3-25 bar) in the presence of a catalyst. The product of this reaction is syngas, which is made up of hydrogen, carbon monoxide (CO), and a small amount of carbon dioxide (CO₂). Next, during a process called the “water-gas shift reaction”, CO reacts with more steam to create additional hydrogen and CO₂. Finally, the CO₂ and any other impurities are removed, leaving nearly pure hydrogen.

Steam Methane Reforming Reaction:

CH₄ + H₂O (+ heat) → CO + 3H₂

How is the nitrogen produced?

Nitrogen is produced through air separation using a process called Fractional Distillation of Liquid Air. First, air is filtered to remove water vapor, and then it is cooled with turbines and refrigeration systems so that gases begin to liquify at different temperatures. CO₂ and other gases condense first, at about −79 °C ( −110 °F). As cooling reaches about −200 °C, the air becomes a cold liquid and is sent to a distillation column that is warmer at the bottom and colder at the top. Oxygen liquifies at −183 °C and flows out from the bottom, while nitrogen, with a lower boiling point of −196 °C, reverts to gas and is collected from the top of the vessel.

Source: Fractional Distillation of Air