How does a factory turn nitrogen from air into ammonia?

Fertilizer production can begin with nitrogen from air, but nitrogen molecules resist chemical change because their bond is strong. The Haber–Bosch process reacts nitrogen with hydrogen to make ammonia. Useful production depends on balancing reaction speed and equilibrium, then separating product and returning unused reactants for another pass.

The reaction is reversible: N₂ + 3 H₂ ⇌ 2 NH₃. At equilibrium, forward and reverse reactions continue at equal rates. Four gas molecules on the reactant side become two on the product side. Compressing an equilibrium mixture at fixed temperature favors the side with fewer gas molecules, increasing the equilibrium share of ammonia rather than guaranteeing complete conversion.

Making ammonia releases heat. Lower temperature favors ammonia at equilibrium, but also slows the reactions, so waiting for a useful output can become impractical. Higher temperature accelerates reaction but leaves a less favorable equilibrium mixture. Industrial operating conditions are a compromise, not a single setting that maximizes every desirable property.

A catalyst supplies an alternative, faster reaction pathway. It speeds approach to equilibrium without changing the equilibrium position. Gas leaving the reactor therefore still contains nitrogen and hydrogen. Cooling separates ammonia as liquid while much of the unreacted gas is returned to the reactor. Removing product between passes and recycling reactants makes useful overall production possible without complete conversion on each pass.

Useful output comes from the connected plant, including purification, compression, heat exchange, separation and recycle. Hydrogen production also uses resources: many established routes use fossil feedstocks, while others use electricity and water. The diagram isolates the reaction-and-recovery loop without specifying operating conditions or environmental performance, showing why reactor conversion per pass is only part of the production story.