New reactor could reduce carbon dioxide emission from ammonia production by half, Joule
Ammonia (NH3) is a very important chemical product. The global production of ammonia is about 200 million tons a year and more than 80% of ammonia are used to make fertilizers. However, the ammonia production process belches out more than 450 million tons of carbon dioxide per year, more than any other industrial chemical reaction. Now, a new type of ceramic reactor designed by Vasileios Kyriakou from the Dutch Institute for Fundamental Energy Research in Eindhoven and his colleagues from Greece could potentially cut the CO2 emission by half.
Traditionally, ammonia is produced via a three-step process. In the first step, steam and methane mix over a solid nickel catalyst at high pressure (100 atm) and high temperatures (up to 1000°C). The catalyst speeds up the chemical reactions that break down the steam and methane and generate molecular hydrogen and carbon monoxide. A second reactor then converts CO, a poison, and steam to more benign CO2 and H2. The final step is the famous iron catalyzed reaction that makes ammonia from hydrogen and nitrogen under high pressure and temperature. (The process is called the Haber-Bosch process and the discovery of its mechanism won the Nobel Prize in 2007.) During the process, huge amount of energy is required to pressurize the reaction tank to the required pressure and heating up the mixture to the desired temperature. Furthermore, the hydrogen produced in the first step would accumulate and decrease the activity of the nickel catalyst, generating more energy lost.
To solve the problem, Vasileios Kyriakou and his colleagues 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, which is the only gas phase product of this reaction, 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. This process of siphoning away the ions shifts the reaction equilibrium and allows the catalyst inside the cylinder to work at a faster rate. The new design could lower the reaction temperature to 600°C and remove the CO conversion step in the Haber-Bosch process. 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.