Fertilisers Get Ready to Reduce CO2 Emissions by 50 % for Ammonia Production
A newly introduced reactor has the capability to combine all three separate reactors used in the current process for producing ammonia into one. The fresh innovation can also reduce carbon dioxide emissions by half which makes it a ‘must have’ in today’s times.
About 90 per cent of ammonia produced is used in fertilisers, to help sustain food production for billions of people around the world. But how is ammonia produced? The physical chemist Fritz Haber from Germany had introduced the cost-efficient Haber-Bosch process or synthetic ammonia process to directly synthesize ammonia from hydrogen and nitrogen. He even won a Noble Prize for Chemistry in 1918 for his achievement and this idea was later developed into a large-scale process by Carl Bosch, an industrial chemist. Bosch made use of a catalyst and high-pressure methods to accomplish this objective.
CO2 emissions in Haber-Bosch process
This unique process’ reaction which runs at temperatures around 500 °C and at pressures up to about 20 MPa, sucks up about 1 % of the world’s total energy production. It belched up to about 451 million tonnes of CO2 in 2010, according to the Institute for Industrial Productivity. That total accounts for roughly 1 % of global annual CO2 emissions, more than any other industrial chemical-making reaction.
New reactor process
Now, a new innovative approach has come to the fore by which carbon dioxide emissions could be cut in halve! Yes, you read that right. The traditional Haber-Bosch process makes use of three separate reactors to produce hydrogen from methane and then pools that hydrogen with nitrogen to create ammonia. In the new approach, all the three reactors have been combined into one which enables to reduce the energy and CO2 footprint.
An article by the American Association for the Advancement of Science in its Science Magazine explains this new process in detail; it states that the first piece of the standard three-step method to making ammonia is known as steam methane reforming. In it, steam and methane mix over a solid nickel catalyst at high pressure and temperatures up to 1000°C. The catalyst speeds chemical interactions that break down the steam and methane and generate molecular hydrogen (H2) and carbon monoxide (CO). A second reactor then converts CO, a poison, and steam to more benign CO2 and H2. Finally, the third reactor transforms the hydrogen and nitrogen to ammonia. But the H2 created in the first reactor slows the work of the nickel catalyst.
To keep the catalyst working at a higher rate, Vasileios Kyriakou, a chemical engineer at the Dutch Institute for Fundamental Energy Research in Eindhoven, and colleagues from Greece sought a reactor design that removes hydrogen atoms as soon as they are stripped off methane molecules. They created a thin tube of ceramic, within which steam and methane mingle as usual. A nickel catalyst on the inner surface of the tube produces positively charged hydrogen ions, electrons, and CO2. The CO2 flows out of the tube as exhaust, and an applied electric voltage pushes the negatively charged electrons through a wire to a second catalyst coating the tube’s outer surface.
This collection of negative charges, in turn, pulls the positively charged hydrogen ions through the wall of the ceramic membrane to the tube’s outer surface. That siphoning away of the ions allows the catalyst inside the cylinder to work at a faster rate. It also allows the reaction to occur at about 600°C, a temperature that produces only CO2 as a byproduct instead of CO that must be processed further.
Meanwhile, on the tube’s outer surface, the second catalyst—which contains vanadium, nitrogen, and iron—causes the hydrogen ions, the electrons, and nitrogen molecules piped in separately to form ammonia, all at atmospheric pressure. The reduced energy needed to drive the reaction let the team create ammonia with just half the CO2 of conventional steam methane reforming.
Discussions are currently being held to explore the possibility of scaling up the new technique and if successful it could also reduce the global price of fertilisers.