The Haber Process: Commercial Uses & Chemistry

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

The Haber Process makes getting nitrogen from the atmosphere a possibility. This lesson will describe the Haber Process before discussing some of the challenges ammonia manufacturers must overcome when using the Haber Process.

Getting Nitrogen from the Air

Nitrogen is a popular element as far as humans are concerned. We use nitrogen in explosives, fertilizers, and cleaners. It's part of making plastics, as well as used as a refrigerant and in oil wells.

Fortunately for us humans, there's plenty of nitrogen. In fact, about 78% of the air around you is made up of nitrogen. The problem though is how to get nitrogen in the air into nitrogen we can use.

Good news! During World War I, German chemist Fritz Haber developed a way to convert nitrogen from the air into ammonia (which is nitrogen attached to some hydrogen atoms). Later, Carl Bosch, another German chemist, improved the technique in order to preform the task on a larger scale.

The Haber Process is named after Fritz Haber
ftizhaber

This process is called the Haber Process, or sometimes the Haber-Bosch Process after the two scientists. This discovery was a pretty big deal and both men were awarded the Noble Prize in 1918.

Haber Process Explained

Before we look at the Haber Process, let's check out the reaction that takes place.

reaction5 caption=

Here, nitrogen and hydrogen gas react with one another under high pressure and temperature to form ammonia. The double arrow shows that this is a reversible reaction, meaning the ammonia be separated back into hydrogen gas and nitrogen gas.

And now, the steps to the Haber Process:

  1. Nitrogen from the air is combined with hydrogen. The hydrogen is often obtained through a reaction with natural gas and steam. Sometimes it is obtained from cracking, or when a larger molecule is broken down into smaller molecules.
  2. The hydrogen and nitrogen gases are sent to the compressor where they are subjected to 200 atmospheres (or 200 times the pressure you're used to right now)
  3. The pressurized gases are then sent to the converter, which heats the gases to around 450 degrees C. The converter contains iron, which is a catalyst, meaning it aides in the reaction but it isn't used up in the reaction. More specifically, the nitrogen and hydrogen react on the iron's surface. Approximately 15% of the hydrogen and nitrogen become ammonia at this point.
  4. The next stop is the cooling tank where ammonia, hydrogen, and nitrogen are cooled, causing the ammonia to turn into a liquid. This ammonia is collected.
  5. The hydrogen and nitrogen then go back into the converter where more ammonia is produced. It's cooled again and the ammonia is collected. This is repeated several times until most of the hydrogen and nitrogen have been transformed into ammonia.

The steps in the Haber Process
haberprocess13

Dynamic Equilibrium

Remember when some of the ammonia turned back into nitrogen and hydrogen gas? Let's delve into that a little more with dynamic equilibrium, or when a reversible reaction reaches a point where the ratio of reactants (or nitrogen and hydrogen gas) to products (or ammonia) does not change. This means that the ratio of reactants to products remains the same.

Why is this important? Well, if you're making ammonia, but some of it changes back into hydrogen and nitrogen gas, it isn't cost-effective.

There is a principle in chemistry referred to as Le Chatelier's Principle, which says you can shift the equilibrium. In other words, by changing things like pressure or temperature, the ammonia manufacturers can shift the equilibrium to the right so when the dynamic equilibrium is reached, more ammonia is produced than would be if those changes were not made.

Make sense? Well, although it seems like a good solution, sometimes what seems easy in chemistry doesn't translate well to the industrial world.

Pressure & Temperature Trade-offs

Let's begin with pressure. If we increase the pressure, the equilibrium will shift to the right, which means we get more ammonia. The problem? Building a facility that can create and withstand high pressures is expensive. You have to have special pipes and tanks, not to mention all of the energy required to generate the immense pressure.

A trade-off is using 200 atmospheres. While more pressure would shift the equilibrium even more, 200 atmospheres is more doable from the standpoint of cost. The 200 atmospheres produces the optimal amount of ammonia when the cost of building and maintaining the facility is considered.

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