Is ammonia the fuel of the future?

A century ago, the world faced a looming food crisis. A booming population was pushing farmers to grow crops faster than nitrogen-fixing bacteria in the soil could keep up, and the South American deposits of guano and natural nitrates they applied as fertilizer were dwindling.

In what may still be the biggest global problem solved by chemistry, Fritz Haber and Carl Bosch developed a process to react hydrogen and atmospheric nitrogen under pressure to make ammonia, which farmers adopted in place of natural fertilizers. The Haber-Bosch process is still responsible for nearly all the world’s ammonia, as well as derivatives like urea and ammonium nitrate.

Today’s crisis is climate change. This time, ammonia could come to the rescue by capturing, storing, and shipping hydrogen for use in emission-free fuel cells and turbines. Efforts are also underway to combust ammonia directly in power plants and ship engines.

Chemical companies smell an opportunity. Several firms are developing green ammonia, a route to ammonia in which hydrogen derived from water electrolysis powered by alternative energy replaces hydrocarbon-based hydrogen, making ammonia production virtually carbon dioxide-free. They are also investing in carbon capture and storage to minimize the carbon impact of making conventional ammonia, creating what the industry refers to as blue ammonia.

Tony Will, CEO of the world’s largest ammonia producer, CF Industries, sees a fundamental shift in the industry’s prospects. “Up to this point, we have made a business by selling the nitrogen value of the molecule,” he says. “What’s really exciting about this is now there is an opportunity and a market that values the hydrogen portion of the molecule.”

But establishing an ammonia fuel industry won’t be easy. By most estimates, green ammonia will cost two to four times as much to make as conventional ammonia. And some of the technologies needed to harness the molecule, such as ammonia-burning engines, are still experimental. Governments and the marketplace will have to decide if green ammonia is worth the effort.

Nature has given ammonia attributes that seem to make it a perfect commodity for a future hydrogen economy.

A report compiled last August by Haldor Topsoe, an ammonia production technology firm, and other companies noted a number of those qualities. Ammonia has a higher energy density, at 12.7 MJ/L than even liquid hydrogen, at 8.5 MJ/L. Liquid hydrogen has to be stored at cryogenic conditions of –253 °C, whereas ammonia can be stored at a much less energy-intensive –33 °C. And ammonia, though hazardous to handle, is much less flammable than hydrogen.

Furthermore, thanks to a century of ammonia used in agriculture, a vast ammonia infrastructure already exists. Worldwide, some 180 million metric tons (t) of ammonia is produced annually, and 120 ports are equipped with ammonia terminals.

But pivoting all that infrastructure toward environmentally friendly fuels will take time. Until last year, most proposed green ammonia projects were small, tens of thousands of metric tons rather than the half-million metric tons per year, or more, than a conventional ammonia plant puts out.

Several are government-supported projects in Australia. For example, the Norwegian fertilizer maker Yara intends to install electrolyzers to make 3,500 t per year of green ammonia at its plant in Pilbara, and the ammonium nitrate explosives makers Dyno Nobel and Queensland Nitrates are studying 9,000 and 20,000 t of green ammonia output, respectively. Pilot programs are also underway in New Zealand and Chile.

Several much larger projects were announced last year. By far the most ambitious one is in Saudi Arabia. The?$5 billion projects?is a partnership between the US company Air Products and Chemicals, the local firm ACWA Power, and NEOM, a developer building a carbon-free city in Saudi Arabia.

Slated for completion in 2025, the installation will sit on the Red Sea coast. Solar cells will harness the sun during the day, while turbines will capture nighttime winds to generate 4 GW of electricity for water electrolysis plants. The hydrogen will be fed into a traditional Haber-Bosch plant to produce 1.2 million t per year of ammonia—a large amount even by conventional standards.

Air Products will spend an additional $2 billion to set up a novel distribution scheme. It will ship the ammonia around the world to specialized plants installed at depots for buses and trucks fueled by hydrogen cells. These units will dissociate the ammonia to recover the hydrogen, enough for up to 15,000 trucks and buses in all.

When Air Products CEO Seifi Ghasemi unveiled the project last summer, he told analysts that he sees it as a feasibility study for an entirely new industry. “We are proud to be part of this undertaking because it is the first and largest and the most innovative project to make mankind’s dream of carbon-free energy a reality,” he said.

Other firms followed suit with big projects.?In October, Yara said it was considering installing electrolyzers at its ammonia plant in Sluiskil, the Netherlands, to generate enough hydrogen for 75,000 t of ammonia. The plant would run on 100 MW of power from a new offshore wind farm.