Invention: Ammonia storage to reduce NOx
A team of Danish researchers developed a method for storing ammonia in solid form by binding it with a compacted metallic salt. Their innovation opens up possibilities for the energy-rich chemical to be used as a safe hydrogen source for fuel cells and hydrogen-powered cars. More importantly, it can be employed as part of systems that remove as much as 99% of the mono-nitrogen oxides from diesel engine exhaust.
Ammonia is like an unco-operative superhero. It has potential to do good - if it weren't so temperamental. Release a steady trickle of ammonia gas into the exhaust system of a diesel engine, and potentially harmful mono-nitrogen oxides (NO and NO2 - collectively known as NOx) are reduced to harmless water vapour and nitrogen. But storing the noxious and caustic chemical is bulky (as a gas), expensive (as a liquid) or both (freezing it to a solid).
Compact, convenient storage for ammonia appeared unlikely until a team of Danish scientists led by Johannessen and Quaade put their heads together and developed an entirely new way to tackle the problem. They discovered how to get certain metal salts, such as strontium chloride, to absorb ammonia like a sponge. In fact, through their process a 100-gram cube of this solid can fit into the palm of one's hand yet contain up to 50 grams of solid ammonia - the equivalent of 60 litres of ammonia gas.
Johannessen, Quaade and co-researchers, who include Claus Hviid Christensen, Jens Kehlet Nørskov and Rasmus Zink Sørensen, have built a business around fighting pollution. Their solid-form ammonia product, marketed under the name AdAmmine, has a number of potential applications. It could be used as a storage device for hydrogen, for instance. That hydrogen, once removed, could then act as a propellant in either an internal combustion engine or in an electric fuel cell. At the moment, however, AdAmmine is most commonly used to neutralise NOx emissions from diesel engines, reducing them by as much as 99% - far beyond what competing technologies can offer.
The team's invention stands to disrupt the status quo. Current urea-based exhaust-scrubbers only start putting out cleaner emissions at temperatures upwards of 200°C. That is not a problem when driving longer distances because engines have time to heat up, but in short-distance city driving, such temperatures are rarely reached. Systems that use AdAmmine begin neutralising NOx pollutants in one-fifth of the time, and if the technology becomes an industry standard for exhaust scrubbing, it has the potential to make the air in and around cities cleaner and safer to breathe.
The advantage of having fewer pollutants in the air is hard to appraise financially. A French Senate committee report estimates that the total effects of all air pollution (not just cars) cost the country some EUR 100 billion annually, citing reduced health as the major expense. It is fair to say that reducing diesel-engine-related smog through technologies such as AdAmmine would have a positive effect on pollution-related costs because transportation makes up about 44% of all NOx pollution.
Assessing the impact of AdAmmine on the automotive market is easier. Already, Amminex has had four successful investment rounds and is reported to have EUR 5.1 million in equity. Its roughly EUR 4.3 million in annual revenue is reinvested, so Amminex is not yet turning a profit, but the company is planning big. It wants to offer an alternative that would replace current AdBlue diesel-scrubbing systems, whose numbers are expected to triple in Europe by 2025.
Tue Johannessen with part of the invention
Tue Johannessen and Ulrich Quaade
Tue Johannessen and Ulrich Quaade with a block of AdAmmine, the compact ammonia storage system
A block of ammonia-binding AdAmmine
Cartridges containing AdAmmine for vehicles
Tue Johannessen and Ulrich Quaade
How it works
The Danish team not only developed the exhaust scrubber systems that can be manufactured as standard features or add-ons to diesel vehicles, they also developed the production process for creating the small metal-salt cubes that store ammonia.
To create these cubes, liquid ammonia is applied to strontium chloride, or another metal salt, at a controlled pressure and temperature to optimise absorption efficiency. As ammonia is absorbed into the lattice of the salt crystal grains, they expand and create a fine powder. The patented Amminex process compresses this powder into a compact cube, which holds many more times the amount of ammonia, by volume, than the powder.
The team found that despite being compacted, when heated the metal ammine salt still releases ammonia at a controllable rate. The first "freed" ammonia molecules on the outer areas of the cube create a network of channels and holes for ammonia from deeper inside the cube to follow.
Tue Johannessen was born on 14 November 1971. He received his PhD in chemical engineering in 1998 from the Technical University of Denmark (DTU), where he went on to work as an associate professor. His colleague, Ulrich Quaade, was also an associate professor at DTU when they spun off a collective research project with Christensen and Nørskov and founded Amminex. Quaade was born on 27 May 1969. He received his PhD in physics from the University of Southern Denmark in 1995. Claus Hviid Christensen, born 31 December 1968, earned a master's degree in chemistry from the University of Copenhagen. Jens Kehlet Nørskov, born 21 September 1952, has a PhD in theoretical physics from the University of Aarhus, Denmark.
Did you know?
Johannessen, Quaade and their co-researchers pay tribute to ammonia in both their product and company names. Ammines (or metal ammine complexes) are compounds comprising a metal and ammonia. Besides acting as a storage vehicle for ammonia, ammines are used for a wide range of applications, from chemotherapy drugs (Cisplatin) to paper treatment. The 2012 European Inventor Award finalists Farouk Tedjar and Jean-Claude Foudraz even put the binding power of ammonia and metals to use in their method for recycling the valuable metals that lithium ion and other batteries contain.