Researchers have developed a method to produce ammonia starting only with air and water. Not only is it more energy efficient than the century-old Haber-Bosch process that’s currently in use, but it’s also greener.
The ability to mass produce Ammonia—made up of three parts hydrogen and one part nitrogen (or NH3)—has had a momentous impact on society. Without the ready availability of this chemical, it is estimated that as many as a third of us won't be alive. This is because its main use is in fertilizer production, which has helped improve crop yields and sustain a large population.
Developed in 1909, the Haber-Bosch process—often cited as the most important invention of the 20th century—involves heating nitrogen and hydrogen gas at very high temperature and pressure in presence of an iron catalyst. The presence of the catalyst, which doesn't take part in the reaction but lowers its energy threshold, is vital. Haber-Bosch was used to produce about 140 million tons of ammonia in 2012, but it consumes nearly two percent of the world's energy supply.
One of the reasons the current production method is inefficient is because it needs hydrogen gas, which is obtained by processing natural gas. The byproduct of the process is also carbon dioxide, which creates other problems. Stuart Licht and his colleagues at George Washington University thought they could do better if they could find a way of using water as a source of hydrogen.
Previous attempts at using water (made up of two parts hydrogen and one part oxygen) with air (which consists of 78 percent nitrogen) to form ammonia have been less successful. Licht's solution was to bubble wet air through a mixture of tiny particles of iron oxide and molten chemicals (sodium and potassium hydroxide) that is zapped with electricity.
Any chemical reaction involves the exchange of electrons among atoms. In this case, the externally supplied electrons are necessary to help split water into hydrogen and oxygen, then combine the hydrogen with nitrogen. "When electricity is applied, the iron oxide captures electrons to permit water and air to directly react to form ammonia," Licht said.
Licht's method claims to use only two-thirds of the energy of the Haber-Bosch process. Along with the elimination of the need to produce hydrogen from natural gas, the overall carbon emissions are reduced quite significantly. The whole process also takes place at milder conditions (Haber-Bosch needs 450°C and 200-times atmospheric pressure).
These are not all that make Licht's method attractive. Some of the energy involved can be supplied by another technology Licht has developed called solar thermal electrochemical production, or STEP. STEP is able to use most of the spectrum of incoming solar energy, making it relatively efficient.
It is one thing to show off the success of chemical production in labs and quite another to replicate it on an industrial scale. Licht admits that there is room for improvement, but he is confident that it could work. David Fermin, professor of electrochemistry at the University of Bristol, added a caveat to Licht’s confidence: "Before going for full scale up, a better understanding of the mechanism in this complex multi-electron transfer reaction will be required."
But even with Licht's method, Fermin points out that we are far away from being able to replicate nature's efficiency at converting nitrogen from the air to useful chemicals. "What is truly remarkable is that nature does it incredibly efficiently at low-temperature," Fermin said, in reference to bacteria that are able to fix nitrogen in the soil.
And yet, if something more efficient can replace the Haber-Bosch process, it would lower the energy input of the production of one of the world's most important chemicals and lead to a notable reduction in global CO2 emissions.
This article originally appeared at The Conversation.