Chemistry:Syngas

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Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide[1] 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.[2][3][4] 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 (in Germany alone, half a million cars were built or rebuilt to run on wood gas).[5]

Production

Syngas is produced by steam reforming or partial oxidation of natural gas or liquid hydrocarbons, or coal gasification.[6]

C + H
2O → CO + H
2[1]
CO + H
2O → CO
2 + H
2[1]
C + CO
2 → 2CO[1]

Steam reforming of methane is an endothermic reaction requiring 206 kJ/mol of energy:

CH
4 + H
2O → CO + 3 H
2

In principle, but rarely in practice, biomass and related hydrocarbon feedstocks could be used to generate biogas and biochar in waste-to-energy gasification facilities.[7] The gas generated (mostly methane and carbon dioxide) is sometimes described as syngas but its composition differs from syngas. Generation of conventional syngas (mostly H2 and CO) from waste biomass has been explored.[8][9]

Composition, pathway for formation, and thermochemistry

The chemical composition of syngas varies based on the raw materials and the processes. Syngas produced by coal gasification generally is a mixture of 30 to 60% carbon monoxide, 25 to 30% hydrogen, 5 to 15% carbon dioxide, and 0 to 5% methane. It also contains lesser amount of other gases.[10] Syngas has less than half the energy density of natural gas.[11]

The first reaction, between incandescent coke and steam, is strongly endothermic, producing carbon monoxide (CO) and hydrogen H2 (water gas in older terminology). When the coke bed has cooled to a temperature at which the endothermic reaction can no longer proceed, the steam is then replaced by a blast of air.

The second and third reactions then take place, producing an exothermic reaction—forming initially carbon dioxide and raising the temperature of the coke bed—followed by the second endothermic reaction, in which the latter is converted to carbon monoxide. The overall reaction is exothermic, forming "producer gas" (older terminology). Steam can then be re-injected, then air etc., to give an endless series of cycles until the coke is finally consumed. Producer gas has a much lower energy value, relative to water gas, due primarily to dilution with atmospheric nitrogen. Pure oxygen can be substituted for air to avoid the dilution effect, producing gas of much higher calorific value.

In order to produce more hydrogen from this mixture, more steam is added and the water gas shift reaction is carried out[12]:

CO + H
2O → CO
2 + H
2

The hydrogen can be separated from the CO
2 by pressure swing adsorption (PSA), amine scrubbing, and membrane reactors. A variety of alternative technologies have been investigated, but none are of commercial value.[13] Some variations focus on new stoichiometries such as carbon dioxide plus methane[14][15] or partial hydrogenation of carbon dioxide. Other research focuses on novel energy sources to drive the processes including electrolysis, solar energy, microwaves, and electric arcs.[16][17][18][19][20][21]

Electricity generated from renewable sources is also used to process carbon dioxide and water into syngas through high-temperature electrolysis. This is an attempt to maintain carbon neutrality in the generation process. Audi, in partnership with company named Sunfire, opened a pilot plant in November 2014 to generate e-diesel using this process.[22]

Syngas that is not methanized typically has a lower heating value of 120 BTU/scf.[23] Untreated syngas can be run in hybrid turbines that allow for greater efficiency because of their lower operating temperatures, and extended part lifetime.[23]

Uses

Syngas is used as a source of hydrogen as well as a fuel[13] (see fuel cell). It is also used to directly reduce iron ore to sponge iron.[24] Chemical uses include the production of methanol which is a precursor to acetic acid and many acetates; liquid fuels and lubricants via the Fischer–Tropsch process and previously the Mobil methanol to gasoline process; ammonia via the Haber process, which converts atmospheric nitrogen (N2) into ammonia which is used as a fertilizer; and oxo alcohols via an intermediate aldehyde.[citation needed]

Environmental impact

The environmental impact of syngas production depends on energy inputs, feedstocks, and processing methods used in production.[25] Studies evaluating syngas environmental impacts include assessments of biogas based reforming systems. This examines how feedstock choice and process conditions influence emissions and overall system efficiency.[26] Production methods that rely on fossil fuel based energy sources are generally associated with higher emissions. Comparing these with biomass or renewable electricity shows a higher emission number when compared.[25] Reported outcomes depend on a number of factors such as land use, supply chain inputs, and system boundaries applied in analysis.[25]

Lifecycle assessments of syngas production have also examined additional environmental indicators including energy demand, resource use and air pollutant emissions.[27] Some studies highlight that upstream activities such as feedstock extraction and transportation can contribute to overall environmental burden.[27] As a result the comparative sustainability of different syngas production systems often depend on tech configuration, regional energy mixes and system efficiency.[28] These findings suggest that environmental performance can vary across all syngas systems but must be evaluated within specific production pathways.

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 Speight, James G. (2002). Chemical and process design handbook. McGraw-Hill handbooks. New York, NY: McGraw-Hill. p. 566. ISBN 978-0-07-137433-0. 
  2. ↑ "Syngas Cogeneration / Combined Heat & Power". http://www.clarke-energy.com/gas-type/synthesis-gas-syngas/. 
  3. ↑ Mick, Jason (3 March 2010). "Why Let it go to Waste? Enerkem Leaps Ahead With Trash-to-Gas Plans". http://www.dailytech.com/Why+Let+it+go+to+Waste++Enerkem+Leaps+Ahead+With+TrashtoGas+Plans/article17817.htm. 
  4. ↑ Boehman, André L.; Le Corre, Olivier (15 May 2008). "Combustion of Syngas in Internal Combustion Engines". Combustion Science and Technology 180 (6): 1193–1206. doi:10.1080/00102200801963417. Bibcode: 2008CST...180.1193B. 
  5. ↑ "Wood gas vehicles: firewood in the fuel tank". 18 January 2010. https://www.lowtechmagazine.com/2010/01/wood-gas-cars.html. 
  6. ↑ Beychok, Milton R. (1974). "Coal gasification and the Phenosolvan process". Am. Chem. Soc., Div. Fuel Chem., Prepr.; (United States) 19 (5). http://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/19_5_ATLANTIC%20CITY_09-74_0085.pdf. 
  7. ↑ "Sewage treatment plant smells success in synthetic gas trial - ARENAWIRE" (in en-AU). 11 September 2019. https://arena.gov.au/blog/logan-gasification-sewage-treatment-plant/. 
  8. ↑ Zhang, Lu (2018). "Clean synthesis gas production from municipal solid waste via catalytic gasification and reforming technology". Catalysis Today 318: 39–45. doi:10.1016/j.cattod.2018.02.050. ISSN 0920-5861. 
  9. ↑ Sasidhar, Nallapaneni (November 2023). "Carbon Neutral Fuels and Chemicals from Standalone Biomass Refineries". Indian Journal of Environment Engineering 3 (2): 1–8. doi:10.54105/ijee.B1845.113223. ISSN 2582-9289. https://www.ijee.latticescipub.com/wp-content/uploads/papers/v3i2/B1845113223.pdf. Retrieved 29 December 2023. 
  10. ↑ "Syngas composition". National Energy Technology Laboratory, U.S. Department of Energy. http://www.netl.doe.gov/research/coal/energy-systems/gasification/gasifipedia/syngas-composition. 
  11. ↑ Beychok, M R (1975). Process and environmental technology for producing SNG and liquid fuels. Environmental Protection Agency. OCLC 4435004117. 
  12. ↑ Afarideh, Mohammad; Esfanjani, Pouya; Sarlak, Faramarz R; Valipour, Mohammad Sadegh (2025). "A review on solar methane reforming systems for hydrogen production". International Journal of Hydrogen Energy 141: 330–347. doi:10.1016/j.ijhydene.2024.08.078. Bibcode: 2025IJHE..141..330A. 
  13. ↑ 13.0 13.1 Hiller, Heinz; Reimert, Rainer; Stönner, Hans-Martin (2011). "Gas Production, 1. Introduction". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a12_169.pub3. ISBN 978-3-527-30673-2. 
  14. ↑ "dieBrennstoffzelle.de - Kvaerner-Verfahren". http://www.diebrennstoffzelle.de/wasserstoff/herstellung/kvaerner.shtml. 
  15. ↑ Kühl, Olaf, "Method and apparatus for producing h2-rich synthesis gas", EU patent 3160899B1, issued 12 December 2018
  16. ↑ "Sunshine to Petrol". Sandia National Laboratories. http://energy.sandia.gov/wp/wp-content/gallery/uploads/S2P_SAND2009-5796P.pdf. 
  17. ↑ "Integrated Solar Thermochemical Reaction System". U.S. Department of Energy. http://www1.eere.energy.gov/solar/sunshot/csp_sunshotrnd_pnnl.html. 
  18. ↑ Matthew L. Wald (April 10, 2013). "New Solar Process Gets More Out of Natural Gas". The New York Times. https://www.nytimes.com/2013/04/11/business/energy-environment/new-solar-process-gets-more-out-of-natural-gas.html. 
  19. ↑ Frances White. "A solar booster shot for natural gas power plants". Pacific Northwest National Laboratory. http://www.pnnl.gov/news/release.aspx?id=981. 
  20. ↑ Foit, Severin R.; Vinke, Izaak C.; de Haart, Lambertus G. J.; Eichel, Rüdiger-A. (8 May 2017). "Power-to-Syngas: An Enabling Technology for the Transition of the Energy System?". Angewandte Chemie International Edition 56 (20): 5402–5411. doi:10.1002/anie.201607552. PMID 27714905. 
  21. ↑ Dammann, Wilbur A., "Method and means of generating gas from water for use as a fuel", US patent 5159900A, issued 3 November 1992
  22. ↑ "Audi in new e-fuels project: synthetic diesel from water, air-captured CO2 and green electricity; "Blue Crude"". Green Car Congress.. 14 November 2014. http://www.greencarcongress.com/2014/11/20141114-audibluecrude.html. 
  23. ↑ 23.0 23.1 Oluyede, Emmanuel O.; Phillips, Jeffrey N. (May 2007). "Volume 3: Turbo Expo 2007". Proceedings of the ASME Turbo Expo 2007: Power for Land, Sea, and Air. Volume 3: Turbo Expo 2007. Montreal, Canada: ASME. pp. 175–182. doi:10.1115/GT2007-27385. ISBN 978-0-7918-4792-3. 
  24. ↑ Chatterjee, Amit (2012). Sponge iron production by direct reduction of iron oxide. PHI Learning. ISBN 978-81-203-4659-8. OCLC 1075942093. 
  25. ↑ 25.0 25.1 25.2 Cao, Guoqiang; Handler, Robert M.; Luyben, William L.; Xiao, Yue; Chen, Chien-Hua; Baltrusaitis, Jonas (2022-08-01). "CO2 conversion to syngas via electrification of endothermal reactors: Process design and environmental impact analysis". Energy Conversion and Management 265. doi:10.1016/j.enconman.2022.115763. ISSN 0196-8904. https://www.sciencedirect.com/science/article/pii/S0196890422005593. 
  26. ↑ "Biogas to Syngas through the Combined Steam/Dry Reforming Process: An Environmental Impact Assessment". doi:10.1021/acs.energyfuels.0c04066. https://pubs.acs.org/doi/10.1021/acs.energyfuels.0c04066. 
  27. ↑ 27.0 27.1 Arvidsson, Maria; Morandin, Matteo; Harvey, Simon (2015-07-15). "Biomass gasification-based syngas production for a conventional oxo synthesis plant—greenhouse gas emission balances and economic evaluation". Journal of Cleaner Production 99: 192–205. doi:10.1016/j.jclepro.2015.03.005. ISSN 0959-6526. https://www.sciencedirect.com/science/article/pii/S095965261500222X. 
  28. ↑ Indrawan, Natarianto; Thapa, Sunil; Bhoi, Prakashbhai R.; Huhnke, Raymond L.; Kumar, Ajay (2017-09-15). "Engine power generation and emission performance of syngas generated from low-density biomass". Energy Conversion and Management 148: 593–603. doi:10.1016/j.enconman.2017.05.066. ISSN 0196-8904. https://www.sciencedirect.com/science/article/pii/S0196890417305228. 



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