If you have been around the ammonia refrigeration industry for a while you know ammonia is clear (colorless) unless it has been contaminated with impurities. However, over the last several years
ammonia is more often being referred to with a color, which is not referring to the ammonia, but the process used to manufacture it. The following is a brief overview of some of the methods of
producing ammonia, which is now an area of intense research and investment:

GRAY AMMONIA SOMETIMES CALLED BROWN AMMONIA

In 1905 German scientist, Fritz Haber published his book on the thermodynamics of technical gas reactions, in which he recorded the production of small amounts of ammonia from N2 (taken from the air) and hydrogen at a temperature of 1000° C with the help of iron as a catalyst. In about 1908 this process was acquired by Badische Anilin- und Sodafabrik (BASF) who tasked and funded their chemist and engineer, Carl Bosch with developing this process on a large industrial scale. This task involved the construction of a production facility and apparatus which would stand up to working at high gas pressure and high reaction temperatures. Bosch’s machine, unveiled in 1914 was able to produce almost 200 pounds of ammonia per hour which is not much but was the beginning of what was to be a very large industry.

Fritz Haber was awarded the Nobel Prize in 1919 for his research that unlocked the ammonia production process. Then in 1931, Carl Bosch and Frederick Bergius were awarded the Nobel Prize for their contributions to the invention and development of chemical high-pressure methods.

The Haber-Bosch process is the most economical for the fixation of nitrogen and with modifications continues in use as one of the basic processes of the chemical industry in the world. The majority of ammonia produced (80% or more) is used as a carrier of nitrogen and is used worldwide as a fertilizer to increase crop

production to sustain and grow the population. The development of the HaberBosch process was critical to the growth of our society since more crops could be grown feeding more and more people.

In this Haber-Bosch process, fossil fuels, typically natural gas, which is CH4, are used (coal is also used.) Both are used to obtain hydrogen in a process of steam methane reforming (SMR) and to power the reaction. It is estimated that for every NH3 molecule generated there is released one molecule of CO2 as a co-product. It has also been stated that there are approximately 2 tons of
CO2 produced for every 1 ton of NH3 produced with some people estimating a ratio closer to 3:1. The Haber-Bosch process is fossil-fuel intense and due to the large amount of CO2 produced
(around 1.8% of global carbon dioxide emissions) in the process this is being called “Gray or Brown Ammonia”.

In addition, due to the widespread use of ammonia as a fertilizer as well as for many other products, it is piped and shipped pretty much all over the world. However, fossil fuels are used for the transport of ammonia which adds to ammonia’s overall carbon footprint. The exact carbon footprint for the production of ammonia depends on the fuel used and the efficiency of the facility, so you could easily identify many shades of grey or brown. Your choice.

GREEN AMMONIA

Green ammonia production is where the process of making ammonia is accomplished using 100% renewable energy sources and is carbon-free. The HaberBosch process is still used to produce ammonia, but water electrolysis which requires a considerable amount of energy is used to generate hydrogen and oxygen, using a sustainable carbon-free method to produce the electricity in the
process. The sustainable and carbon-free power sources might be solar, wind, hydroelectric, or possibly nuclear.

There is considerable interest in “Green Ammonia” for several reasons, besides being zero-carbon. One, as an energy source, ammonia has approximately nine times the energy of lithium-ion batteries. Two, it is 1.8 times more energy-dense than liquid hydrogen. Three, ammonia is much easier to transport and store than liquid hydrogen using existing technology and infrastructure.

Green ammonia is now one of the main fuels being considered by the maritime sector to enable the shipping industry to meet new CO2 reduction targets proposed by 2030 and 2050. For cargo ships, ammonia would be used as fuel for their engines and in fuel cells. Also, because ammonia has a high density of hydrogen, and is easy to transport it can be shipped to a point
of intended use and then “cracked” to
produce pure hydrogen that can be used as a fuel source.

BLUE AMMONIA

Blue ammonia is made from nitrogen again taken from the air and hydrogen again derived from natural gas feedstocks just as with “Grey Ammonia”. After almost 100 years the production process has improved in efficiency but is still CO2 intense. However, the reason this process is identified as “Blue Ammonia” is because of what happens to the carbon dioxide by-product from
hydrogen production.

One method to reduce CO2 is to capture and store it underground or use it in some other process. The storage of CO2 is challenging due to the resources required and the space or location for storage. The other suggested method is to plant trees to offset the CO2 that is released, which seems like a fair idea since due to forest fires over the last many years a lot of trees need to
be replaced. In this case, someone has to estimate the number of trees to be planted to hopefully more than offset the CO2 being released. That has to be a lot of trees!

Depending on the fuel used, the share of CO2 captured, and the upstream methane emissions from natural gas exploitation, this “blue ammonia” process may range from pale to dark, or from, say, sky blue to navy blue. Still blue but potentially many different shades.

BLUE-GREEN AMMONIA OR SOMETIMES REFERRED TO AS “TURQUOISE AMMONIA”

As the name implies, this process is a combination of fossil fuel and carbon-free production. There is still, depending on the process, CO2 released that must be used in another process or captured and stored.

In this process, methane is used as a feedstock, but the process is driven by heat produced with sustainable and carbon-free electricity rather than through the combustion of fossil fuels.
This methane pyrolysis produces hydrogen and carbon as outputs, however, unlike steam methane reforming (SMR), the carbon is in solid form rather than a gas. As a result, there is no requirement for carbon capture and storage and the carbon can even be used in other applications. Where the electricity driving the pyrolysis is renewable, the process is
zero-carbon, or even carbon negative if the feedstock is biomethane rather than fossil methane (natural gas).

Fossil fuels are used for the transport of ammonia which adds to ammonia’s overall carbon footprint. The exact carbon footprint for the production of ammonia depends on the fuel used and the efficiency of the facility, so you could easily identify many shades of grey or brown. Your choice.

Methane pyrolysis greatly reduces the requirement for electricity estimated at 10-20 kWh per kg of hydrogen, versus 60 kWh for electrolysis. The production of “Turquoise Ammonia” may be a good alternative to “Grey” or “Blue” ammonia production processes, especially as the process improves resulting in very little or no carbon released.

LESSON LEARNED:

There is a tremendous amount of interest and investment going into how to produce ammonia with a much lower or zero carbon footprint. Whatever the color of the ammonia production process is called, for the industrial refrigeration industry we still will get the anhydrous ammonia we know and love which is one of the best refrigerants available.