3.1 UN Sustainable Development Goals in practice: zero hunger

One of the most important industrial chemicals is ammonia (represented by the chemical formula, NH₃).

Ammonia is prepared, on a massive scale using the Haber–Bosch process.

The chemistry at the heart of the Haber-Bosch process is the reaction of two gases, nitrogen and hydrogen, which may be represented by the following chemical equation.

But why is this reaction so important in the context of the SDG 2? Video 3 in the activity below provides some answers.

Activity 1 The Haber–Bosch process

Timing: Allow about 10 minutes

Watch the video and then answer the question that follows.

Download this video clip.Video player: Video 3

Show transcript | Hide transcript

Transcript: Video 3 The Haber–Bosch process

DAVID COLE-HAMILTON

And here I have on the slide the Haber–Bosch process. Now, the Haber–Bosch process takes nitrogen from the air, reacts it with hydrogen and converts it into ammonia, and ammonia is used as a fertiliser.

Now, this is the most important chemical reaction in the world. It’s done on an enormous scale, 175 million tonnes a year. But a really interesting and remarkable thing is that 80% of the nitrogen in our bodies, in our proteins, in our amino acids, comes through this process. It’s not natural nitrogen coming from outside. It’s nitrogen coming from the Haber–Bosch process through plants when it’s put on as a fertiliser, and then, eventually, we eat the plants, or we eat animals that have eaten the plants.

With this process and other agricultural chemicals, which have to be extremely selective so they only do the job you want them to do, they have to be extremely active so we only use a small amount of them, they have to be non-toxic so they don’t poison anybody, half the world is kept alive.

If we didn’t have agricultural chemicals, we would not be able to support the 8 billion people in the world. We would only be able to support about 4 billion. So it’s an amazingly important reaction, really important.

But there are some disadvantages. It uses 1.8% of all the energy used in the world. That’s huge. It’s equivalent to the energy used by 144 million people in a year.

And the reason for this is partly because of the way the hydrogen is made. At the moment, you take methane, natural gas, it goes through a process called steam reforming, which produces hydrogen and carbon monoxide. The carbon monoxide is then treated in something called the water–gas shift process, and that produces more hydrogen and carbon dioxide.

So all of that carbon in the methane is converted to carbon dioxide, which is thrown away. And that is 5% of all the methane used in the world is used in this one process. It’s amazing. And all of the carbon from that methane is thrown away. And 1.8% of all the carbon dioxide that we generate is produced in this process.

Now, this is terrible. If we could stop that carbon dioxide being emitted into the atmosphere, we would really be able to tackle some parts of global warming. So one challenge is, can we change the process by which we make the hydrogen? And in principle, it’s very easy.

If we can do water electrolysis so you take water, you pass electricity through it, and I’m going to talk about this in a bit more detail later on, you produce hydrogen and oxygen, no carbon involved. And that would completely get rid of this problem of using the methane, the large amounts of methane, and producing the large amounts of carbon dioxide.

Another aspect is the chemistry. Because this is entropically unfavored, it means that you have to run it at low temperature. You put a catalyst in, and the catalyst system is shown there. That catalyst was developed by Alwin Mittasch.

And he worked extremely hard for the Bosch company. And I think he looked at 20,000 different combinations to produce this catalyst. And that’s the catalyst that’s still used.

But it’s not fast enough. So they have to run at high temperature. And when they run at high temperature, they have a low equilibrium position. So they have to recycle everything all the time. So it’s an enormously inefficient reaction.

So another area where people could perhaps improve this is by changing the catalyst or even by doing some special heating of the catalyst, which only heats the catalyst and doesn’t heat the flowing stream. And then you can hope to get a higher position for the equilibrium at lower temperature.

Now, this is being tried in some places, and it could make an enormous difference. And so there’s an enormous amount of work to do in this process. What I’m going to do in this lecture is I’m going to give you opportunities, which I think chemists have, to help in these kinds of reactions. So my first opportunity is to develop and commercialise low-temperature, low-energy routes, low-carbon routes to fertilisers.

There is another problem with ammonia, and that is the way it’s supplied. It’s supplied in large quantities to fields, and it flows off into streams and rivers and causes eutrophication. Eutrophication is the development of green algae, which you can see in this river here. And eutrophication stops the oxygen going into the water. And so plant life and fish in the water cannot survive. So it’s really very, very bad.

Ammonia also causes air pollution. It creates nitric oxide, which causes smog. And it also can cause ozone depletion.

So there are very important things to do here. Can you apply the ammonia only to the plants that need it, not in a blanket way all over the field? I show you here a drone which is spraying individual plants. And you can actually have a drone which will look at the plants and say, those all look healthy, that one doesn’t look very well, we’ll put some ammonia onto that.

Now, that probably isn’t the way it’s going to be done. But that’s the kind of thing we need to think about. And here we need to collaborate with other people. We need to collaborate with agriculturalists to make this work. And that’s why I’ve put here a sustainable development goal, 17 partnerships for the goals. And here’s another opportunity to work with these people to get ammonia application specific to individual plants.

End transcript: Video 3 The Haber–Bosch process

Download

Video 3 The Haber–Bosch process

Interactive feature not available in single page view (see it in standard view).

Professor Cole-Hamilton refers to the Haber-Bosch process as the ‘most important chemical reaction in the world’. How does he justify this statement?

Answer

Ammonia is essential for production of agricultural fertilisers essential for feeding the world’s population. Fertilisers are used to make plant protein, which we either eat directly, or via animals - in fact 80% of the nitrogen in our bodies originates from industrially produced ammonia.

As discussed in Video 3, a chemical balancing act is required when selecting the ideal conditions for this reaction. So, let’s summarise the challenges faced by chemists.

Challenges faced by chemists

As a general rule chemical reactions go faster as the temperature is raised. High temperatures do indeed increase reaction rate, but they also favour the reverse reaction which sees ammonia being converted back into nitrogen and hydrogen.

So, as discussed in Video 3, on balance, a moderate temperature with the addition of a catalyst and operating at high pressures is the preferred option.

But that’s not all.

You also learned the production of ammonia is incredibly energy intensive, the main reason for this lies with one of the raw materials – hydrogen,

The other feedstock, nitrogen, isn’t a problem, there’s plenty of it available in the air, but as described in Video 2 hydrogen has to be prepared by a chemical reaction on a vast scale which is hugely costly in terms of its energy requirement.