Recently, we posted articles about the Hydrogen molecule and it’s potential. Now, at Proton Ventures, we are specialized in ammonia, which is a molecule composed of hydrogen and nitrogen. Now, we would like to look at the other component of the ammonia molecule, Nitrogen.
Let’s start with a few facts regarding nitrogen:
- Nitrogen is all around us.
- Nitrogen is an essential components of all life forms, without which life as we know it would not exist.
- Nitrogen sits the base of our food system
- Lack of nitrogen has been the biggest limiting factor to population growth for centuries
- Nitrogen is directly responsible for 4% of human-induced greenhouse gas emissions.
- Nitrogen is a major pollutant to ecosystems and to human health.
All the facts listed above, although some are contradictory, are all true facts about nitrogen and nitrogen compounds, which is also why I find it so interesting. The key to understand here is that nitrogen exists in many different forms in nature. By the end of this article, you will understand why all of the earlier statements are true and why nitrogen is so interesting and critical.
Let’s start with the first point, is it true that nitrogen is all around us?
In the air around us, 78% is nitrogen, in the form of a molecule called di-nitrogen, or N2 for its molecular formula. Dinitrogen is 2 atoms of nitrogen attached together by a triple chemical bond. In this form, nitrogen is totally inert and therefore it barely reacts with anything. That is why it is all around us but it barely impacts us. The low reactivity is due to its triple bond that is extremely hard to break. It takes 974kJ/mol of energy to break this this bond. To put it into perspective, it takes the equivalent of a day of electricity consumption by a typical 4-people Dutch household to provide enough energy to theoretically break all the nitrogen triple bonds present in a cubic meter of air, if there were no losses.
Due to its low reactivity, pure nitrogen is often used as an inerting gas in many industrial processes. That way, any reaction between the process piping and any atmospheric components are avoided. An example of these is purging critical piping with pure dinitrogen before loading/unloading operations..
Ok but if nitrogen has such a low reactivity, how can it be at the base of life?
Luckily, nitrogen exists in nature in other forms than di-nitrogen (N2). For instance, all proteins that compose our muscles are so-called amino-acids, which have a nitrogen atom in their chemical formula. Nitrogen is also deeply embedded in our DNA, as nitrogenous bases compose all the 4 building blocks of DNA. So without Nitrogen, no DNA and no proteins, hard for life, isn’t it?
But where does the nitrogen in our proteins and our DNA come from?
It comes from the atmosphere.
Wait what? Didn’t we just say that di-nitrogen is inert?
Yes, but luckily there are natural mechanisms to make di-nitrogen react. These mechanisms are mostly the following 2 mechanisms:
- Enzymatic reactions: Some bacteria contain an enzyme called nitrogenase, that has evolved the ability to break the nitrogen triple bond and produce ammonium, or NH4+. Legumes such as lentils, peanuts, beans, chickpeas, alpha-alpha are notorious for hosting nitrogenases within their roots, making them a very precious source of nitrogen for other life forms. Once produced, ammonium can easily be converted to proteins and DNA.
- Lighting: When lighting travels through the atmosphere, it carries so much energy that it breaks many di-nitrogen molecules in its path, which routinely recombine with oxygen to form nitrous oxides (NO, NO2 and N2O), so-called NOx. These nitrous oxides can then form nitrates (NO3–) that can be used by life-forms to form proteins and DNA.
In the following graph, we can see the flows of nitrogen between the atmosphere and other reservoirs.
We can see from this picture that almost 60MT of Nitrogen per year are fixed by enzymes in the soil and 5MT/y are fixed by lighting.±
So if there are natural ways to fix nitrogen, why has lack of nitrogen limited human population growth for centuries?
Natural ecosystems have evolved to live with nitrogen provided by the enzymes and by lighting and to efficiently recycle nitrogen in soils. However, with the development of agriculture, traditional agricultural practices have been depleting nitrogen in the soil without recycling it back to the soil, which caused agricultural yields to drop. The figure beside from Yara shows the impact on plant growth from the deficiency of nitrogen in the soil (plant on the right side).
Our ancestors had already learned thousands of years ago that recycling agricultural wastes and manures to the fields was boosting agricultural production. In fact, what they were doing was simply recycling back the nitrogen to allow plants to grow. But with increased populations, these primitive fertilizing practices were not sufficient anymore, and humanity discovered other fossil sources of nitrogen, such as Peruvian Guano (basically bird poop), in the second part of the 19th century. However, these were still finite resources and could only provide limited amounts of nitrogen to humanity.
Come 1898, when a landmark speech by Sir Albert Crookes in front of the British Royal Society outlined that if humanity did not find a way to fix atmospheric nitrogen by itself, it would face wide-scale starvation by 1930. That speech sparked major research in synthetic nitrogen fixation.
4 years later, in 1902, 2 Norwegian researchers, Kristian Birkeland and Samuel Eyde, developed the Birkeland-Eyde process, in which they managed to reproduce the effect of lighting in a laboratory to produce nitrates (NO3-) in a reactor, which was the first successful process invented to fix atmospheric nitrogen. However, the energy efficiency of this process was very low, making the fixed nitrogen very expensive. To put it into perspective, it took about a month of electricity consumption by a typical 4 persons Dutch household to break all the di-nitrogen molecules in one cubic meter of air using the Birkeland-Eyde process.
A few years later, in 1909, Fritz Haber proved experimentally that by reacting pure nitrogen and pure hydrogen at high pressure and high temperature on an Osmium-based catalyst, he could produce ammonia (NH3) in a lab with a significantly more energy efficient process. A few years after that, Carl Bosch improved upon Fritz Haber’s design and changed the catalyst to an Iron-based catalyst, to patent the Haber-Bosch process in 1913. The Haber-Bosch process was so energy efficient that it became economically viable to fix nitrogen for fertilizing agricultural fields.
Finally, humanity to managed liberate itself from the limitation of low nitrogen content in soils!!
The Haber-Bosch process is still the process used today to fix atmospheric nitrogen. As shown on the graph beside, it is estimated that without the invention of the Haber-Bosch process, half of the current human population would not be able to be fed.
I hope that you are now convinced that nitrogen really sits at the base of our food systems and that it has almost single-handedly solved hunger worldwide.
Ok now that nitrogen has helped humanity to solve hunger, why is nitrogen also responsible of 4% of human induced greenhouse gas emissions?
The main process to fix atmospheric nitrogen currently, the Haber-Bosch process, requires input of pure hydrogen, as mentioned earlier. During Fritz Haber and Carl Bosch time, the main process to produce hydrogen was coal gasification, which emitted about 25 ton CO2 per ton hydrogen. During the 20th century, most hydrogen production switched to a cleaner process, namely steam methane reforming, which emits 9 ton CO2 per ton hydrogen. That’s an improvement from previously, but still not a very clean process. In fact, hydrogen production as input to ammonia production is currently responsible for 1,5% of the global greenhouse gas emissions.
Furthermore, ammonia by itself is not a very convenient fertilizer and is rarely applied directly as a fertilizer. Most of the time, ammonia is first converted to other nitrogen-based fertilizers like urea (CO(NH2)2 ) or ammonium nitrate NH4NO3). Here, a new problem appears with the production of ammonium nitrate through the Oswald process. This process has an unfortunate by-product, which is nitrous oxide (N2O), otherwise called “laughing gas”. Nitrous oxide has a global warming potential of 298, meaning that every kilogram of nitrous oxide emitted has the same global warming effect than 298 kilograms of CO2. Here we can see that even very small emission streams of nitrous oxide can have major implications for the fight against climate change. That is why most ammonium nitrate plants in the western world are retrofitted with a so-called “de-NOx” system, which uses ammonia to neutralize nitrous oxide.
The nitrous oxide is not only a problem in ammonium nitrate production, but also on farmlands. Indeed, when nitrogen fertilizers are applied in excess on an area with a deficiency of oxygen, nitrous oxide gets formed and emitted to the atmosphere. This process is a major contributor to agriculture-related greenhouse gas emissions, accounting for almost 2% of global greenhouse gas emissions.
Combining the 3 emission streams outlined above, (1) ammonia production, (2) nitrous oxide emissions in fertilizer production and (3) nitrous oxide emissions on the farm, these emission streams together account for about 4% of the global greenhouse gas emissions, and are therefore a major front in the fight against climate.
Luckily, solutions exist for all 3 emission streams.
- To address the emissions related to hydrogen production, hydrogen could be produced through water electrolysis, thereby removing carbon from the ammonia value chain entirely. That would be so-called “green hydrogen”. Alternatively, existing steam methane could be retrofitted with state-of-the-art carbon capture and storage (CCS) systems, that could capture up to 80% of the life-cycle carbon emissions.
- Regarding the emissions of ammonium nitrate production, all the ammonium nitrate plants should be retrofitted with de-NOx systems, as mentioned earlier.
- To address nitrous oxide emissions on farmland, digital solutions do exist to apply the right fertilizer in the right amount and at the right time to maximize plant uptake and avoid nitrogen leaking. More generally, responsible application of fertilizer is increasingly common practice in the western world, and we can see from the chart beside that fertilizer use per capita has already peaked worldwide since the 1980s and is reducing in the western world..
Now, we mentioned at the introduction of the article that on top of contributing to the greenhouse effect, nitrogen can also be dangerous for ecosystems and human health? Why is that?
Let’s come back to over-fertilization. When ammonium nitrate is applied on farmlands, it breaks down into ammonium (NH4+) and nitrates (NO3-). Nitrates are very soluble to water, meaning that when applied in excess, nitrates will not fix onto the soil but instead leak away in water. In highly fertilized areas, nitrate leaching is routinely well above 50% of total nitrogen applied. When large amounts of nitrate leak into rivers and lakes, it causes algal blooms due to over-fertilization of natural ecosystems. Some of these algal blooms can release toxic substances that are lethal to other species, including humans in large quantities.
Furthermore, when these algae die out, they decompose in lakes and consume the oxygen disolved in water. That create anoxic water conditions, in which all other life forms are wiped out. This chain of natural processes is called “eutrophication” and is responsible for the destruction of large swaths of river, lake and coastal ecosystems. One large-scale example of eutrophied environment is the Baltic sea. Once a very rich and thriving marine ecosystem, the Baltic sea has been transformed into a dead zone in the 1980s due to over-fertilisation and has not recovered since. The Netherlands also has eutrophied areas in the Ijsselmeer, part of the so-called “stickstoff problem”, that has been widely publicized in the media.
Beyond eutrophication, over-fertilisation also causes volatilisation of nitrogen monoxide (NO) and nitrogen dioxide (NO2), which are grouped under the term NOx and are responsible for acidic rains.
Nitrous oxides (NOx) are also dangerous for humans living in cities. Indeed, combustion engines in cars as well as power plants emit quite a lot of these NOx. In a typical combustion processes, very hot areas are created, in which a very small amounts of nitrogen triple bonds get broken down and recombine with oxygen to produce the aforementionned NOx. These nitrogen oxides can cause irritations for the respiratory systems and can even be carcinogenic in case of regular exposure. In cities with large car traffic, NOx concentrations reach levels that are dangerous to human health in the long term. This problem also has multiple solutions. Chief among all is the transition to electric cars, that will make our cities a lot healthier as electric cars do not have NOx emissions during use. For the current car fleet, selective catalytic reduction (SCR) is often installed using AdBlue to abate the NOx emissions. Regarding power plants, De-NOx solutions using ammonia exist to abate the NOx emissions and a lot of modern power plants have those systems in place.
Now that we have clarified all the challenges, controversies and opportunities related nitrogen, what are the main nitrogen compounds and what is their economic importance?
The basis of the current nitrogen economy is ammonia (NH3), which is the molecule from which all other nitrogen compounds are being produced. Ammonia is the molecule produced by the Haber-Bosch process, introduced earlier. Worldwide, around 190 million ton of ammonia are produced annually, making ammonia the second most produced chemical in the world, only behind sulfuric acid. It is expected that ammonia would be the world most produced chemical by 2030 and estimates suggest that global ammonia production will reach 500-1100 million tons annually by 2050.
Ammonia is currently used directly as a coolant in most industrial refrigeration systems for example or to bind NOx in De-NOx system, thereby abating these harmful emissions. Ammonia is also sometimes mixed with water to make aqueous ammonia, making the cleaning product that most people are familiar with. Most ammonia (about 98%) is however transformed into other nitrogen compounds to fuel the nitrogen economy. Chief among them is urea, for which 65% of global ammonia production is converted to.
Urea is the world’s most utilized fertilizer because it has a high nitrogen content, it is solid and safe to transport at ambient conditions. The only challenge with urea is that it releases carbon dioxide once applied to the fields, meaning it contributes to climate change and is likely to be phased out as a fertilizer in the coming decades. Urea is also a precursor to melamine (C3H6N6), which is a building blocks for hard plastics used in home furniture for example. Urea is also the main component of Ad Blue, which abates NOx emissions of cars in cities.
Beyond urea, a lot of ammonia (25%) is converted to ammonium nitrate ( NH4NO3). Ammonium nitrate is a fertilizer that has the advantage of breaking down into ammonium (NH4+) and nitrate (NO3-) when applied in the fields. Ammonium is taken up quickly by plants whereas nitrates have a longer absorption, making one application of ammonium nitrate long-lasting on the fields. The ammonium nitrate used for fertilizer is mostly high density amonium nitrate.
Ammonim nitrate is famous as an explosive substance, meaning that it needs to be treated with the highest safety standards. The high-profile accidents of Beiruth in 2020 or Toulouse in 2001 have both been caused by ammonium nitrate. These explosive characteristics can be amplified by prilling the substance to low densities to produce explosives such as TNT, nitroglycerine or dynamite, for the mining sector.
It is also possible to combine ammonium nitrate and urea, in a solution called Urea-Ammonium Nitrate, commonly known as UAN. UAN is a liquid high-end fertilizer in many parts of the world, combining the properties of both molecules. Other valuable nitrogen compounds include ammonium sulfate, calcium ammonium nitrate, ammonium phosphate, NPK, which are all considered high-end fertilizers, providing multiple nutrients to plants. In the industrial sector, there are thousands of nitrogen compounds based on ammonia used for use cases as diverse as glues (urea formaldehyde), amino-acids (acetonitrile), plastics (caprolactam), etc..
In the future, it is expected that ammonia use will surge due to new sectors that will use it for decarbonization. The shipping sector, which is currently responsible for 3% of the global CO2 emissions, will likely use ammonia to replace fuel oil. Ammonia can partially decarbonize coal and gas power plants by being co-fired alongside the main fuel. That reduces the consumption of the carbonated fuel and is a short-term quick-fix for these plants. Finally and maybe most importantly, ammonia can be used as a hydrogen carrier to transport renewable energy across the world, thereby not only unlocking the nitrogen economy, but also the clean hydrogen economy. From steel production to heavy mobility through cement production, glass production or petroleum refining, the clean hydrogen economy can substitute up to 20% of the global greenhouse gas emissions.
This shows that nitrogen and nitrogen compounds play a very important role in large parts of the global economy, starting with food production, going through mining the metals necessary to power the digital and energy transition, the shipping sector, electricity production, all hydrogen use-cases and a lot more.
As we can see since the start of this article, Nitrogen is a major cause of climate change and ecosystem destruction, but with the right combination of technologies and the right processes, nitrogen and ammonia provide very important solutions to the challenges facing humanity in the 21st century.
This is where Proton Ventures comes into the picture.
Proton Ventures is an engineering company specialized on ammonia. We support our clients from the base of the nitrogen economy (ammonia production) and it’s application across the various nitrogen compounds. We use our technical knowledge to support the companies that are leveraging nitrogen and ammonia to build a decarbonized and emission-free future.
For instance, we help project developers with designing future green ammonia production plants, including the choice of technologies, the supplier selection, the management of intermittency, the plant sizing and phasing, the safety process definition, the material selection, process optimization, etc., which makes these plants safe and competitive.
Furthermore, ammonia needs to reach the end-consumer, meaning an increasing number of ammonia storage terminals will be needed to unlock the nitrogen economy. Proton Ventures has designed and built multiple ammonia storage facilities, and therefore helps it’s clients daily to ensure safe, emissions-free and energy efficient terminal designs.
Finally, nitric acid, ammonium nitrate, Caprolactam, UAN and all other nitrogen compounds will also increasingly have to be produced with clean processes, for which Proton Ventures is always ready to provide it’s experts to advise, design and make projects happen.
If you need support with technical knowledge regarding ammonia or any of the nitrogen compound, don’t hesitate to reach out to Proton Ventures.