Ammonia production

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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]

Contents

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).

Block flow diagram of the ammonia synthesis process AmmoniaSynthesisDiagram.png
Block flow diagram of the ammonia synthesis process

Frank–Caro process

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.

[6]

Birkeland–Eyde process

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 nitride, which when combined with water produce metal hydroxide and ammonia.

Haber-Bosch process

This section is an excerpt from Haber process.[ edit ]
Fritz Haber, 1918 Fritz Haber.png
Fritz Haber, 1918

The Haber process, [7] also called the Haber–Bosch process, is the main industrial procedure for the production of ammonia. [8] [9] It converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2) using a finely divided iron metal catalyst:

This reaction is slightly favorable in terms of enthalpy, but is disfavored in terms of entropy because four equivalents of reactant gases are converted into two equivalents of product gas. As a result, high pressures and moderately high temperatures are needed to drive the reaction forward.

The German chemists Fritz Haber and Carl Bosch developed the process in the first decade of the 20th century, and its improved efficiency over existing methods such as the Birkeland-Eyde and Frank-Caro processes was a major advancement in the industrial production of ammonia. [10] [11] [12] The Haber process can be combined with steam reforming to produce ammonia with just three chemical inputs: water, natural gas, and atmospheric nitrogen. Both Haber and Bosch were eventually awarded the Nobel Prize in Chemistry: Haber in 1918 for ammonia synthesis specifically, and Bosch in 1931 for related contributions to high-pressure chemistry.

Environmental Impacts

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. [13] Ammonia production also introduces nitrogen into the Earth's nitrogen cycle, causing imbalances that contribute to environmental issues such as algae blooms. [14] [15] [16] Certain production methods prove to have less of an environmental impact, such as those powered by renewable or nuclear energy. [16]

Sustainable production

Illustrating inputs and outputs of methane pyrolysis, a process to produce hydrogen. Methane Pyrolysis-1.png
Illustrating inputs and outputs of methane pyrolysis, a process to produce hydrogen.

Sustainable production is possible by using non-polluting methane pyrolysis or generating hydrogen by water electrolysis with renewable energy sources. [17] Thyssenkrupp Uhde Chlorine Engineers expanded its annual production capacity for alkaline water electrolysis to 1 gigawatt of electrolyzer capacity for this purpose. [18]

Illustrating inputs and outputs of simple electrolysis of water, for production of hydrogen. Hydrogen production via Electrolysis.png
Illustrating inputs and outputs of simple electrolysis of water, for production of hydrogen.

In a hydrogen economy some hydrogen production could be diverted to feedstock use. For example, in 2002, Iceland produced 2,000 tons of hydrogen gas by electrolysis, using excess power from its hydroelectric plants, primarily for fertilizer. [19] The Vemork hydroelectric plant in Norway used its surplus electricity output to generate renewable nitric acid from 1911 to 1971, [20] requiring 15 mWh/ton of nitric acid. The same reaction is carried out by lightning, providing a natural source of soluble nitrates. [21] Natural gas remains the lowest cost method.

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. [22] This may become a potentially sustainable source of ammonia given its abundance. [23] Alternatively, ammonia from wastewater can be sent into an ammonia electrolyzer (ammonia electrolysis) operating with renewable energy sources to produce hydrogen and clean water. [24] Ammonia electrolysis may require much less thermodynamic energy than water electrolysis (only 0.06 V in alkaline media). [25]

Another option for recovering ammonia from wastewater is to use the mechanics of the ammonia-water thermal absorption cycle. [26] [27] 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

The Process to make ammonia from coal Ammoniafromcoal.png
The Process to make ammonia from 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. [28]

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. [29] [30]

Green ammonia

In 2024, the BBC announced numerous companies were attempting to reduce the 2% of global carbon dioxide emissions caused by the use/production of ammonia by producing the product in labs. The industry has become known as "green ammonia." [31]

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. [32] 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. [33] [34]

See also

Related Research Articles

<span class="mw-page-title-main">Ammonia</span> Chemical compound

Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the formula NH3. A stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pungent smell. Biologically, it is a common nitrogenous waste, and it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to fertilisers. Around 70% of ammonia produced industrially is used to make fertilisers in various forms and composition, such as urea and diammonium phosphate. Ammonia in pure form is also applied directly into the soil.

<span class="mw-page-title-main">Haber process</span> Industrial process for ammonia production

The Haber process, also called the Haber–Bosch process, is the main industrial procedure for the production of ammonia. It converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2) using a finely divided iron metal catalyst:

Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principally used for producing ammonia or methanol. Syngas is combustible and can be used as a fuel. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII.

<span class="mw-page-title-main">Gasification</span> Form of energy conversion

Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.

<span class="mw-page-title-main">Alternative fuel</span> Fuels from sources other than fossil fuels

Alternative fuels, also known as non-conventional and advanced fuels, are fuels derived from sources other than petroleum. Alternative fuels include gaseous fossil fuels like propane, natural gas, methane, and ammonia; biofuels like biodiesel, bioalcohol, and refuse-derived fuel; and other renewable fuels like hydrogen and electricity.

<span class="mw-page-title-main">Sabatier reaction</span> Methanation process of carbon dioxide with hydrogen

The Sabatier reaction or Sabatier process produces methane and water from a reaction of hydrogen with carbon dioxide at elevated temperatures and pressures in the presence of a nickel catalyst. It was discovered by the French chemists Paul Sabatier and Jean-Baptiste Senderens in 1897. Optionally, ruthenium on alumina makes a more efficient catalyst. It is described by the following exothermic reaction:

<span class="mw-page-title-main">Methanol economy</span> Economic theory

The methanol economy is a suggested future economy in which methanol and dimethyl ether replace fossil fuels as a means of energy storage, ground transportation fuel, and raw material for synthetic hydrocarbons and their products. It offers an alternative to the proposed hydrogen economy or ethanol economy, although these concepts are not exclusive. Methanol can be produced from a variety of sources including fossil fuels as well as agricultural products and municipal waste, wood and varied biomass. It can also be made from chemical recycling of carbon dioxide.

Coal liquefaction is a process of converting coal into liquid hydrocarbons: liquid fuels and petrochemicals. This process is often known as "Coal to X" or "Carbon to X", where X can be many different hydrocarbon-based products. However, the most common process chain is "Coal to Liquid Fuels" (CTL).

<span class="mw-page-title-main">Gas to liquids</span> Conversion of natural gas to liquid petroleum products

Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies exist: (i) direct partial combustion of methane to methanol and (ii) Fischer–Tropsch-like processes that convert carbon monoxide and hydrogen into hydrocarbons. Strategy ii is followed by diverse methods to convert the hydrogen-carbon monoxide mixtures to liquids. Direct partial combustion has been demonstrated in nature but not replicated commercially. Technologies reliant on partial combustion have been commercialized mainly in regions where natural gas is inexpensive.

<span class="mw-page-title-main">Industrial gas</span> Gaseous materials produced for use in industry

Industrial gases are the gaseous materials that are manufactured for use in industry. The principal gases provided are nitrogen, oxygen, carbon dioxide, argon, hydrogen, helium and acetylene, although many other gases and mixtures are also available in gas cylinders. The industry producing these gases is also known as industrial gas, which is seen as also encompassing the supply of equipment and technology to produce and use the gases. Their production is a part of the wider chemical Industry.

Water gas is a kind of fuel gas, a mixture of carbon monoxide and hydrogen. It is produced by "alternately hot blowing a fuel layer [coke] with air and gasifying it with steam". The caloric yield of the fuel produced by this method is about 10% of the yield from a modern syngas plant. The coke needed to produce water gas also costs significantly more than the precursors for syngas, making water gas technology an even less attractive business proposition.

Hydrogen gas is produced by several industrial methods. Nearly all of the world's current supply of hydrogen is created from fossil fuels. Most hydrogen is gray hydrogen made through steam methane reforming. In this process, hydrogen is produced from a chemical reaction between steam and methane, the main component of natural gas. Producing one tonne of hydrogen through this process emits 6.6–9.3 tonnes of carbon dioxide. When carbon capture and storage is used to remove a large fraction of these emissions, the product is known as blue hydrogen.

Methanation is the conversion of carbon monoxide and carbon dioxide (COx) to methane (CH4) through hydrogenation. The methanation reactions of COx were first discovered by Sabatier and Senderens in 1902.

Carbon-neutral fuel is fuel which produces no net-greenhouse gas emissions or carbon footprint. In practice, this usually means fuels that are made using carbon dioxide (CO2) as a feedstock. Proposed carbon-neutral fuels can broadly be grouped into synthetic fuels, which are made by chemically hydrogenating carbon dioxide, and biofuels, which are produced using natural CO2-consuming processes like photosynthesis.

Power-to-gas is a technology that uses electric power to produce a gaseous fuel. When using surplus power from wind generation, the concept is sometimes called windgas.

Lower-temperature fuel cell types such as the proton exchange membrane fuel cell, phosphoric acid fuel cell, and alkaline fuel cell require pure hydrogen as fuel, typically produced from external reforming of natural gas. However, fuels cells operating at high temperature such as the solid oxide fuel cell (SOFC) are not poisoned by carbon monoxide and carbon dioxide, and in fact can accept hydrogen, carbon monoxide, carbon dioxide, steam, and methane mixtures as fuel directly, because of their internal shift and reforming capabilities. This opens up the possibility of efficient fuel cell-based power cycles consuming solid fuels such as coal and biomass, the gasification of which results in syngas containing mostly hydrogen, carbon monoxide and methane which can be cleaned and fed directly to the SOFCs without the added cost and complexity of methane reforming, water gas shifting and hydrogen separation operations which would otherwise be needed to isolate pure hydrogen as fuel. A power cycle based on gasification of solid fuel and SOFCs is called an Integrated Gasification Fuel Cell (IGFC) cycle; the IGFC power plant is analogous to an integrated gasification combined cycle power plant, but with the gas turbine power generation unit replaced with a fuel cell power generation unit. By taking advantage of intrinsically high energy efficiency of SOFCs and process integration, exceptionally high power plant efficiencies are possible. Furthermore, SOFCs in the IGFC cycle can be operated so as to isolate a carbon dioxide-rich anodic exhaust stream, allowing efficient carbon capture to address greenhouse gas emissions concerns of coal-based power generation.

E-diesel is a synthetic diesel fuel for use in automobiles. Currently, e-diesel is created at two sites: by an Audi research facility Germany in partnership with a company named Sunfire, and in Texas. The fuel is created from carbon dioxide, water, and electricity with a process powered by renewable energy sources to create a liquid energy carrier called blue crude which is then refined to generate e-diesel. E-diesel is considered to be a carbon-neutral fuel as it does not extract new carbon and the energy sources to drive the process are from carbon-neutral sources.

<span class="mw-page-title-main">Power-to-X</span> Storing surplus electricity production in chemical form

Power-to-X are electricity conversion, energy storage, and reconversion pathways from surplus renewable energy. Power-to-X conversion technologies allow for the decoupling of power from the electricity sector for use in other sectors, possibly using power that has been provided by additional investments in generation. The term is widely used in Germany and may have originated there.

Liquid Nitrogen Wash is a process mainly used for the production of ammonia synthesis gas within fertilizer production plants. It is usually the last purification step in the ammonia production process sequence upstream of the actual ammonia production.

<span class="mw-page-title-main">Reversible solid oxide cell</span>

A reversible solid oxide cell (rSOC) is a solid-state electrochemical device that is operated alternatively as a solid oxide fuel cell (SOFC) and a solid oxide electrolysis cell (SOEC). Similarly to SOFCs, rSOCs are made of a dense electrolyte sandwiched between two porous electrodes. Their operating temperature ranges from 600°C to 900°C, hence they benefit from enhanced kinetics of the reactions and increased efficiency with respect to low-temperature electrochemical technologies.

References

  1. ↑ Congressional Research Service. (7 December 2022). "Ammonia’s Potential Role in a Low-Carbon Economy". CRP website Retrieved 24 September 2023.
  2. ↑ "Global ammonia annual production capacity".
  3. ↑ "Mitsubishi Heavy Industries BrandVoice: Scaling Ammonia Production for the World's Food Supply". Forbes .
  4. ↑ Koop, Fermin (2023-01-13). "Green ammonia (and fertilizer) may finally be in sight -- and it would be huge". ZME Science. Retrieved 2023-03-21.
  5. ↑ Congressional Research Service. (7 December 2022). "Ammonia’s Potential Role in a Low-Carbon Economy". CRP website Retrieved 24 September 2023.
  6. 1 2 "Introduction to Ammonia Production". www.aiche.org. 2016-09-08. Retrieved 2021-08-19.
  7. ↑ Habers process chemistry. India: Arihant publications. 2018. p. 264. ISBN   978-93-131-6303-9.
  8. ↑ 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. ISBN   978-0-306-40895-3.
  9. ↑ Appl, Max (2006). "Ammonia". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a02_143.pub2. ISBN   978-3527306732.
  10. ↑ Smil, Vaclav (2004). Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production (1st ed.). Cambridge, MA: MIT. ISBN   978-0-262-69313-4.
  11. ↑ 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. ISBN   978-0-307-35178-4.
  12. ↑ Sittig, Marshall (1979). Fertilizer Industry: Processes, Pollution Control, and Energy Conservation. Park Ridge, New Jersey: Noyes Data Corp. ISBN   978-0-8155-0734-5.
  13. ↑ Mayer, Patricia; Ramirez, Adrian; Pezzella, Giuseppe; Winter, Benedikt; Sarathy, S. Mani; Gascon, Jorge; Bardow, André (2023-08-18). "Blue and green ammonia production: A techno-economic and life cycle assessment perspective". iScience. 26 (8): 107389. Bibcode:2023iSci...26j7389M. doi:10.1016/j.isci.2023.107389. PMC   10404734 . PMID   37554439.
  14. ↑ Glibert, Patricia M; Maranger, Roxane; Sobota, Daniel J; Bouwman, Lex (2014-10-01). "The Haber Bosch–harmful algal bloom (HB–HAB) link". Environmental Research Letters. 9 (10): 105001. Bibcode:2014ERL.....9j5001G. doi:10.1088/1748-9326/9/10/105001. ISSN   1748-9326.
  15. ↑ Erisman, Jan Willem; Galloway, James N.; Seitzinger, Sybil; Bleeker, Albert; Dise, Nancy B.; Petrescu, A. M. Roxana; Leach, Allison M.; de Vries, Wim (2013-07-05). "Consequences of human modification of the global nitrogen cycle". Philosophical Transactions of the Royal Society B: Biological Sciences. 368 (1621): 20130116. doi:10.1098/rstb.2013.0116. ISSN   0962-8436. PMC   3682738 . PMID   23713116.
  16. 1 2 Li, Yifei; Zhang, Zongyue; Wang, Qingrui; Long, Xiangtao; Cao, Yuwei; Yang, Haiping; Yang, Qing (2023-11-01). "The nitrogen and carbon footprints of ammonia synthesis in China based on life cycle assessment". Journal of Environmental Management. 345: 118848. doi:10.1016/j.jenvman.2023.118848. ISSN   0301-4797. PMID   37660421.
  17. ↑ Lumbers, Brock (2022). "Mathematical modelling and simulation of the thermo-catalytic decomposition of methane for economically improved hydrogen production". International Journal of Hydrogen Energy. 47 (7): 4265–4283. doi:10.1016/j.ijhydene.2021.11.057. S2CID   244814932 . Retrieved 16 March 2022.
  18. ↑ "Water Electrolysis > Products > Home". Uhde Chlorine Engineers. Archived from the original on 2021-10-19. Retrieved 2021-12-08.
  19. ↑ "Iceland launches energy revolution". BBC News. 2001-12-24. Archived from the original on 7 April 2008. Retrieved 2008-03-23.
  20. ↑ Bradley, David (2004-02-06). "A Great Potential: The Great Lakes as a Regional Renewable Energy Source" (PDF). Archived from the original (PDF) on 29 October 2008. Retrieved 2008-10-04.
  21. ↑ Karl Fisher; William E. Newton (2002). G. J. Leigh (ed.). Nitrogen fixation at the millennium . Elsevier. pp.  2–3. ISBN   978-0-444-50965-9.
  22. ↑ "StackPath". www.waterworld.com. March 2010.
  23. ↑ 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. PMID   29406102.
  24. ↑ Muthuvel, Madhivanan; Botte, Gerardine G (2009). "Trends in Ammonia Electrolysis". Modern Aspects of Electrochemistry, No. 45. Vol. 45. pp. 207–245. doi:10.1007/978-1-4419-0655-7_4. ISBN   978-1-4419-0654-0.
  25. ↑ Gwak, Jieun; Choun, Myounghoon; Lee, Jaeyoung (February 2016). "Alkaline Ammonia Electrolysis on Electrodeposited Platinum for Controllable Hydrogen Production". ChemSusChem. 9 (4): 403–408. Bibcode:2016ChSCh...9..403G. doi:10.1002/cssc.201501046. PMID   26530809.
  26. ↑ Lin, P.; Wang, R.Z.; Xia, Z.Z.; Ma, Q. (June 2011). "Ammonia–water absorption cycle: a prospective way to transport low-grade heat energy over long distance". International Journal of Low-Carbon Technologies. 6 (2): 125–133. doi: 10.1093/ijlct/ctq053 .
  27. ↑ 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. S2CID   115749773.
  28. ↑ "Das Zweidruckverfahren von Uhde - Düngemittelanlagen". Industrial Solutions (in German). Retrieved 2021-12-08.
  29. ↑ "Ajinomoto Co., Inc., UMI, and Tokyo Institute of Technology Professors Establish New Company to implement the World's First On Site Production of Ammonia". Ajinomoto . 27 April 2017. Retrieved 22 November 2021.
  30. ↑ "Technology / Business Introduction". Tsubame BHB. 27 April 2017. Retrieved 22 November 2021.
  31. ↑ Baraniuk, Chris (27 February 2024). "Why firms are racing to produce green ammonia". BBC News.
  32. ↑ "This is exactly why we're running out of CO2 for beer and meat production". iNews. 2018-06-28.
  33. ↑ "Why is there a CO2 shortage and how will it hit food supplies?". BBC News. 2021-09-20. Retrieved 2021-09-21.
  34. ↑ "Gas crisis: No chance lights will go out, says government". BBC News. 2021-09-20. Retrieved 2021-09-21.

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