Which feature of a typical reactor in the Haber process allows very high maximum percentage yields to be achieved?
The Haber process is the way that most of the world’s ammonia is produced. It involves the reaction of nitrogen and hydrogen at around 450 degrees Celsius, 200 atmospheres, with an iron-based catalyst. Here’s the equation for the equilibrium. One nitrogen molecule reacts with three hydrogen molecules to produce two ammonia molecules. However, even in these extreme conditions, the equilibrium yield is still only about 30 percent. So, the question is which feature of a reactor in the Haber process allows for much higher percentage yields than this 30 percent?
At the start of the Haber process, nitrogen and hydrogen gases are put into a mixer. This mixture is channeled into the compressor, which takes it close to the pressure it needs to be for the reactor. Inside the reactor, the high pressure, high temperature, and the catalyst help to produce large quantities of ammonia. However, because our equilibrium yield is limited to 30 percent, we still have plenty of nitrogen and hydrogen.
So, this mixture of gases is channeled into a cooler. This removes ammonia from the gas mixture because it becomes a liquid. This liquid can then be separated. So, do we just vent the nitrogen and hydrogen gases and start with a whole new batch? Well, we haven’t figured out what step actually increases the practical yield we can achieve.
Instead of being vented and wasted, the reactants, the nitrogen and hydrogen, are recycled back into the reactor system. It is the recycling of the reactants back into the system that gives a practical yield of about 97 percent. So, a feature of the reactor system in the Haber process that allows high maximum percentage yields is the recycling of reactants.