Ammonia production takes place worldwide, mostly in large-scale manufacturing plants that produce 183 million metric tonnes[1] of ammonia (2021) annually.[2][3] Leading producers are China (31.9%), Russia (8.7%), India (7.5%), and the United States (7.1%). 80% or more of
ammonia is used as
fertilizer. Ammonia is also used for the production of plastics, fibres, explosives, nitric acid (via the
Ostwald process), and intermediates for dyes and pharmaceuticals. The industry contributes 1% to 2% of global CO 2.[4] Between 18–20 Mt of the gas is transported globally each year.[5]
History
Dry distillation
Before the start of
World War I, most ammonia was obtained by the dry
distillation of nitrogenous vegetable and animal products; by the reduction of
nitrous acid and
nitrites with
hydrogen; and also by the decomposition of ammonium salts by alkaline hydroxides or by
quicklime, the salt most generally used being the chloride (
sal-ammoniac).
Adolph Frank and Nikodem Caro found that Nitrogen could be fixed by using the same
calcium carbide produced to make
acetylene to form calcium-cyanamide, which could then be divided with water to form ammonia.
The method was developed between 1895 and 1899.
While not strictly speaking a method of producing ammonia, nitrogen can be fixed by passing it (with oxygen) through an electric spark.
Nitrides
Heating metals such as magnesium in an atmosphere of pure nitrogen produces
the nitride, which when combined with water produce the metal hydroxide and ammonia.
The
Haber process,[7] also called the Haber–Bosch process, is the main industrial procedure for the production of ammonia.[8][9] The German chemists
Fritz Haber and
Carl Bosch developed it in the first decade of the 20th century. The process converts atmospheric
nitrogen (N2) to
ammonia (NH3) by a reaction with
hydrogen (H2) using an
iron metal catalyst under high temperatures and pressures. This reaction is slightly
exothermic (i.e. it releases energy), meaning that the
reaction is favoured at lower temperatures[10] and higher pressures.[11] It decreases
entropy, complicating the process. Hydrogen is produced via
steam reforming, followed by an iterative closed cycle to react hydrogen with nitrogen to produce ammonia.
The primary reaction is:
Before the development of the Haber process, it had been difficult to produce ammonia on an industrial scale,[12][13][14] because earlier methods, such as the
Birkeland–Eyde process and the
Frank–Caro process, were too inefficient.
Because ammonia production depends on a reliable supply of
energy, fossil fuels are often used, contributing to climate change when they are combusted and create
greenhouse gasses.[15] Ammonia production also introduces nitrogen into the Earth's nitrogen cycle, causing imbalances that contribute to environmental issues such as algae blooms.[16][17][18] Certain production methods prove to have less of an environmental impact, such as those powered by renewable or nuclear energy.[18]
Sustainable production
Sustainable production is possible by using non-polluting
methane pyrolysis or generating hydrogen by
water electrolysis with
renewable energy sources.[19]Thyssenkrupp Uhde Chlorine Engineers expanded its annual production capacity for alkaline water electrolysis to 1 gigawatt of electrolyzer capacity for this purpose.[20]
Wastewater is often high in ammonia. Because discharging ammonia-laden water into the environment damages marine life,
nitrification is often necessary to remove the ammonia.[24] This may become a potentially sustainable source of ammonia given its abundance.[25] Alternatively, ammonia from wastewater can be sent into an ammonia electrolyzer (ammonia
electrolysis) operating with renewable energy sources to produce hydrogen and clean water.[26] Ammonia electrolysis may require much less thermodynamic energy than water electrolysis (only 0.06 V in alkaline media).[27]
Another option for recovering ammonia from wastewater is to use the mechanics of the ammonia-water thermal absorption cycle.[28][29] Ammonia can thus be recovered either as a liquid or as ammonium hydroxide. The advantage of the former is that it is much easier to handle and transport, whereas the latter has commercial value at concentrations of 30 percent in solution.
Coal
Making ammonia from coal is mainly practised in China, where it is the main source.[6] Oxygen from the air separation module is fed to the gasifier to convert coal into synthesis gas (H2, CO, CO2) and CH4. Most gasifiers are based on fluidized beds that operate above atmospheric pressure and have the ability to utilize different coal feeds.
Production plants
The American Oil Co in the mid-1960s positioned a single-converter ammonia plant engineered by
M. W. Kellogg at Texas City, Texas, with a capacity of 544 m.t./day. It used a single-train design that received the “Kirkpatrick Chemical Engineering Achievement Award” in 1967. The plant used a four-case centrifugal compressor to compress the
syngas to a pressure of 152 bar Final compression to an operating pressure of 324 bar occurred in a reciprocating compressor. Centrifugal compressors for the synthesis loop and refrigeration services provided significant cost reductions.
Almost every plant built between 1964 and 1992 had large single-train designs with syngas manufacturing at 25–35 bar and ammonia synthesis at 150–200 bar. Braun Purifier process plants utilized a primary or tubular reformer with a low outlet temperature and high
methane leakage to reduce the size and cost of the reformer. Air was added to the secondary reformer to reduce the methane content of the primary reformer exit stream to 1–2%. Excess nitrogen and other impurities were erased downstream of the methanator. Because the syngas was essentially free of impurities, two axial-flow ammonia converters were used. In early 2000 Uhde developed a process that enabled plant capacities of 3300 mtpd and more. The key innovation was a single-flow synthesis loop at medium pressure in series with a conventional high-pressure synthesis loop.[30]
Small-scale onsite plants
In April 2017, Japanese company Tsubame BHB implemened a method of ammonia synthesis that could allow economic production at scales 1-2 orders of magnitude below than ordinary plants with utilizing electrochemical catalyst.[31][32]
Green ammonia
In 2024, the
BBC announced numerous companies were attempting to reduce the 2% of
global carbon emissions caused by the use/production of ammonia by producing the product in labs. The industry has become known as "green ammonia."[33]
Byproducts and shortages due to shutdowns
One of the main industrial byproducts of ammonia production is
CO2. In 2018, high oil prices resulted in an extended summer shutdown of European ammonia factories causing a commercial
CO2 shortage, thus limiting production of CO2-based products such as beer and soft drinks.[34] This situation repeated in September 2021 due to a 250-400% increase in the wholesale price of natural gas over the course of the year.[35][36]
^Habers process chemistry. India: Arihant publications. 2018. p. 264.
ISBN978-93-131-6303-9.
^Appl, M. (1982). "The Haber–Bosch Process and the Development of Chemical Engineering". A Century of Chemical Engineering. New York: Plenum Press. pp. 29–54.
ISBN978-0-306-40895-3.
^Clark 2013, "The forward reaction (the production of ammonia) is exothermic. According to Le Chatelier's Principle, this will be favoured at a lower temperature. The system will respond by moving the position of equilibrium to counteract this – in other words by producing more heat. To obtain as much ammonia as possible in the equilibrium mixture, as low a temperature as possible is needed".
^Clark 2013, "Notice that there are 4 molecules on the left-hand side of the equation, but only 2 on the right. According to Le Chatelier's Principle, by increasing the pressure the system will respond by favouring the reaction which produces fewer molecules. That will cause the pressure to fall again. To get as much ammonia as possible in the equilibrium mixture, as high a pressure as possible is needed. 200 atmospheres is a high pressure, but not amazingly high".
^Smil, Vaclav (2004). Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production (1st ed.). Cambridge, MA: MIT.
ISBN978-0-262-69313-4.
^Hager, Thomas (2008). The Alchemy of Air: A Jewish genius, a doomed tycoon, and the scientific discovery that fed the world but fueled the rise of Hitler (1st ed.). New York, New York: Harmony Books.
ISBN978-0-307-35178-4.
^Sittig, Marshall (1979). Fertilizer Industry: Processes, Pollution Control, and Energy Conservation. Park Ridge, New Jersey: Noyes Data Corp.
ISBN978-0-8155-0734-5.
^Huang, Jianyin; Kankanamge, Nadeeka Rathnayake; Chow, Christopher; Welsh, David T.; Li, Tianling; Teasdale, Peter R. (January 2018). "Removing ammonium from water and wastewater using cost-effective adsorbents: A review". Journal of Environmental Sciences. 63: 174–197.
doi:
10.1016/j.jes.2017.09.009.
PMID29406102.
^Shokati, Naser; Khanahmadzadeh, Salah (August 2018). "The effect of different combinations of ammonia-water Rankine and absorption refrigeration cycles on the exergoeconomic performance of the cogeneration cycle". Applied Thermal Engineering. 141: 1141–1160.
Bibcode:
2018AppTE.141.1141S.
doi:
10.1016/j.applthermaleng.2018.06.052.
S2CID115749773.