Haber process

The Haber process, also called the Haber–Bosch process, is the main industrial way we make ammonia. Ammonia is very important because it is used to make fertilizers that help plants grow. The process takes nitrogen from the air and hydrogen and mixes them together using a special helper called a catalyst, which is made from iron. This creates ammonia through a special chemical reaction.

This reaction gives off heat, but it is tricky because it needs a lot of pressure and high temperature to work well. The process was invented by two German chemists, Fritz Haber and Carl Bosch, in the early 1900s. They made it much better than older ways of making ammonia, like the Birkeland–Eyde and Frank–Caro processes.

The Haber process can be used together with another process called steam reforming to make ammonia using just water, natural gas, and air. Both Haber and Bosch were recognized for their work by winning the Nobel Prize in Chemistry: Haber in 1918 for creating the ammonia process, and Bosch in 1931 for his work on high-pressure chemistry.

History

Main article: History of the Haber process

In the 19th century, people needed more nitrates and ammonia for growing plants and making things. They got these from digging up special rocks and bird droppings from islands. But by the early 1900s, people thought these supplies would run out. Scientists looked for new ways to make ammonia from the air.

A scientist named Haber, with help from Robert Le Rossignol, made a special machine that could change air into ammonia. They showed it worked in 1909. A big company in Germany bought the idea and made it bigger so factories could use it. By 1913, they were making ammonia on a large scale. This was very important during World War I because it helped Germany make things they needed, even when other countries tried to stop them.

Process

Making ammonia needs a lot of energy. It uses about 1–2% of all the energy in the world, and it creates some pollution too. To make ammonia, we need hydrogen gas and nitrogen from the air. Hydrogen is usually made from natural gas, but it can also come from coal, water, or other sources.

Special materials called catalysts help turn hydrogen and nitrogen into ammonia. Scientists have found new catalysts that work better or need lower temperatures. The main way to make hydrogen right now is by using natural gas, but there are other ways being studied too.

Hydrogen production

The main source of hydrogen is natural gas. We heat and treat the gas to get hydrogen out of it. There are also ways to make hydrogen without using fuels that create pollution, like using water and electricity.

Ammonia production

Hydrogen and nitrogen are mixed together and passed over a catalyst to make ammonia. This process needs high pressure and temperature to work well. The gases are cooled after each step so ammonia can be separated out as a liquid. The leftover gases go back into the process to make more ammonia.

Catalysts

The Haber–Bosch process uses special materials called catalysts to help turn nitrogen from the air into ammonia. These catalysts are solid pieces that work with gases.

The most common catalyst is made from tiny pieces of iron. This iron is prepared very carefully to make it work well. It starts as a special kind of iron ore and is treated to create small, porous pieces that help the reaction happen faster. Other materials are added to help the iron stay effective.

Catalysts other than iron

Scientists have tried many different metals to use besides iron. Some, like ruthenium, work well but need special treatments to be useful. Ruthenium can work at lower pressures and temperatures, but it can also have problems, like turning carbon supports into methane gas.

Catalyst poisons

Certain impurities in the gases used can hurt the catalysts. Some of these impurities, like sulfur and chlorine, can stop the catalyst from working forever. Others, like water or carbon monoxide, temporarily slow it down. Even harmless gases can build up and make the reaction slower by taking up space.

Industrial production

Synthesis parameters

The Haber process makes ammonia from nitrogen and hydrogen gases. This happens through a special reaction that needs high pressure and temperature to work well. The basic reaction looks like this: nitrogen plus three hydrogen molecules can change into two ammonia molecules. This reaction gives off heat, but it needs high pressure to make more ammonia.

To make this reaction work, we use a special material called a catalyst, usually made from iron. The catalyst helps the reaction happen faster, but we still need high temperatures around 450 to 550 °C. The process also needs a lot of pressure, between 250 to 350 bar, to get the best results. The gases are mixed in a ratio of one part nitrogen to three parts hydrogen.

Large-scale implementation

Modern factories can make more than 3000 tons of ammonia every day using one production line. Before the reaction, the gases need to be very clean. Impurities like certain gases can stop the catalyst from working well.

To get the hydrogen needed, methane gas is mixed with water vapor. This makes carbon monoxide and hydrogen. Then, more methane is mixed with oxygen to make even more hydrogen. Finally, carbon monoxide is changed into carbon dioxide, which is removed so it doesn’t cause problems later.

The gases are then compressed to the right pressure and sent into a reactor where the ammonia is made. The ammonia is separated from the other gases and cleaned before it’s ready to use.

Mechanism

Elementary steps

The Haber process makes ammonia from nitrogen and hydrogen gas. It uses a special material called a catalyst to help the reaction happen. The process has several steps:

1. The gases move to the catalyst surface.
2. The gases stick to the catalyst.
3. The gases react on the catalyst.
4. The ammonia leaves the catalyst.

The slowest step is breaking apart the nitrogen molecule, which needs a lot of energy. This step decides how fast the whole process goes.

Energy diagram

The energy needed for the reaction can be shown in a diagram. Without a catalyst, breaking apart nitrogen would need too much energy. The catalyst helps by holding onto the nitrogen atoms, making the reaction possible at normal temperatures. Even with the catalyst, breaking apart nitrogen is still the slowest step because it needs a lot of energy to start.

Economic and environmental aspects

Further information: Ammonia production § Sustainable production

When it was first created, the Haber process was compared to another method called the cyanamide process. The cyanamide process used a lot of electricity and needed more work than the Haber process.

By 2018, the Haber process made 230 million tonnes of ammonia per year. This ammonia is mostly used as a fertilizer in three forms: as ammonia itself, as ammonium nitrate, and as urea. The process uses 3–5% of the world's natural gas, which is about 1–2% of all the energy we use worldwide. Together with better plant breeding and chemicals that protect plants, these fertilizers have helped farms grow more food on the same amount of land.

However, the process uses a lot of energy, which can harm the environment. It can cause problems like extra nitrates getting into water, creating areas in the ocean where sea creatures cannot live, and increasing a gas in the air that helps trap heat. The Haber process has added a lot of extra reactive nitrogen to the world, changing natural patterns. Because not all the nitrogen used by farms is taken up by plants, much of it runs off into the environment, disturbing natural habitats.

Almost half of the nitrogen in our bodies today comes from the Haber process. It has helped the world’s population grow from 1.6 billion in 1900 to 7.7 billion by 2018. New technology using reverse fuel cell methods could make ammonia without needing to separately create hydrogen first.

Using synthetic fertilizers means farmers sometimes do not use crop methods that naturally add nitrogen to the soil, like planting certain plants together.