Emerging Voices: Ammonia: A Century After Haber-Bosch

Halfway into his 2022 book How the World Really Works, scientist and policy analyst Vaclav Smil attempts a bold task: to definitively list the four material pillars of modern civilization (1). These pillars are cement, steel, plastics, and ammonia. He considers other important materials like silicon, lumber, and stone, but, in the end, he emphasizes these four above others for the uniquely important roles they play in every aspect of modern life. Without them, the world would be a profoundly less habitable, comfortable, advanced, and organized place.

As chemical engineers, we are intimately familiar with how integral ammonia is to the modern world, but to the average person, it might seem out of place on this list. Most people are in physical contact with steel, cement, or plastic for the majority of their waking hours, but ammonia’s impact is easily overlooked. Although ammonia has many uses in refrigerants, sanitation, alternative energy, and as a feedstock, between 75% and 90% of produced ammonia is used in synthetic fertilizers, without which it would be impossible to feed modern populations (2). Synthetic-­ammonia-based fertilizers restore vital nitrogen to soil that is often stripped of nutrients through modern farming practices. “Only an impossibly complete recycling of all wastes voided by grazing animals could, together with near-perfect recycling of all other sources of organic nitrogen, provide the amount of nitrogen annually applied to crops in ammonia-­based fertilizers,” says Smil (1).

Since its first commercial operation in 1913, the Haber-Bosch process has been the primary means of synthesizing ammonia. In this process, atmospheric nitrogen (N₂) is converted to ammonia (NH₃) by a reaction with hydrogen (H₂) at high temperatures and pressures over an iron-based catalyst. This highly exothermic reaction requires plenty of energy, and ammonia production accounts for between 1% and 2% of all global carbon emissions (2). Therefore, decreasing ammonia’s carbon intensity has been a goal of chemical engineers for many decades. Today, synthetic ammonia remains the backbone of the world’s food supply, and many breakthroughs have already helped reduce its carbon intensity.

Decarbonizing Haber-Bosch. Engineers have taken many routes to decrease ammonia’s carbon intensity. Some of these technologies have been featured in CEP, including August 2019’s “Renewable Hydrogen for Sustainable Ammonia Production,” which...