December 03, 2021

Better than hydrogen: Does NH3 beat the miracle cure of defossilization?

Climate-neutral transport, chemicals, heating and basic industries: hydrogen is supposed to be a promise, a hope that despite the energy turnaround not everything has to change and that we can continue to use the existing infrastructures. If we want to produce emission-free crude steel, polymers and building materials in the future, there is hardly any way around the lightest of all gases. But how H2 capable is industry?


The gas is an "old acquaintance" for the process industry, and gas storage facilities and pipelines are proven concepts. Still, it is not quite that simple, unfortunately, because hydrogen, of all things, doesn't make it easy for us in the seemingly parade disciplines of transport and storability: the molecule diffuses through or into materials and tries leaks and embrittlement. Moreover, while the mass-specific energy density ("heating value") of hydrogen is a whopping 33.3 kWh/kg, it only has volume-specific energy density at three Wh/l.


Power-to-gas advocates have high hopes for alternative storage solutions, such as metal hydride storage in which gas is dissolved under pressure in metals or alloys. However, gas uptake and release is slow, and large amounts of metal are needed to store small amounts of gas. This leaves liquid organic hydrogen carriers or LOHCs (liquid organic hydrogen carriers), which are organic compounds that can absorb and release hydrogen, but in practice the temperatures required limit the usability of hydrocarbons.


Ammonia from electrolysis hydrogen: electricity storage of the future?


Ammonia (NH3) is one of the oldest "bulk chemicals" and is produced worldwide in the order of hundreds of millions of tons for the production of fertilizers. In the Haber-Bosch process, nitrogen and hydrogen react on an iron catalyst, with the necessary H2 usually obtained by steam reforming from natural gas or coal. First ammonia projects pick up speed.


That could easily be changed, if the H2 molecules were obtained by electrolysis rather than from fossil hydrocarbons, ammonia could become "green." Such projects could defossilize fertilizer production and provide an alternative storage pathway for renewable energy: Ammonia can be burned in modified gas and steam turbines or internal combustion engines and could become an alternative to fuel oil and natural gas for gas-fired power plants or marine propulsion.

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