Jump to content

Coal tar

From Wikipedia, the free encyclopedia
(Redirected from Coal-tar)

Coal tar
Clinical data
Trade namesBalnetar, Cutar, others
Other namesliquor carbonis detergens (LCD)
liquor picis carbonis (LPC)[1]
AHFS/Drugs.comMultum Consumer Information
Routes of
administration		Topical
ATC code
Legal status
Legal status
  • US: OTC / Rx-only
Identifiers
CAS Number
ChemSpider
  • none
UNII
CompTox Dashboard (EPA)
ECHA InfoCard100.029.417 Edit this at Wikidata

Coal tar is a viscous dark liquid that is a by-product of deriving coke and coal gas from coal.[2][3] Coal tar has long been a source of useful chemicals as well as a general wood preservative. Although not common, it is used topically for relief from some skin conditions.[4][5]

History

[edit]

Coal tar has been produced since about 1665.[6] Much later, in the production of coke and illumination gases ("town gas"), it was an undesirable byproduct. Soon it was found to be a source of solvents.[7] Around 1850, it was discovered that it could be used as a source of many organic compounds. Its use as a precursor to dyes engendered an entire industry.[8] In 1854 Frederick Crace Calvert, "an eminent English chemist", made the extraordinary statement before the Society of Arts that "ere long, some valuable dyeing substances would be prepared from coal."[9] Coal tar was used for medical purposes as early as the 1800s.[10] Coal tar was a component of the first sealed roads. In its original development by Edgar Purnell Hooley, tarmac was tar covered with granite chips. Later the filler used was industrial slag.

Economics

[edit]

The value of the trade in coal tar is around US$20 billion per year (2023).[11] As of 2011, 30M tons of coal tar were obtained per year, half of which was processed as a source of chemicals.

Some British companies included:[12][13]

Production

[edit]

Coal tar is produced through thermal destruction (pyrolysis or carbonization) of coal, usually with the objective of obtaining coke, which is heavily used in the production of iron and steel. The composition of coal tar varies with the process and type of coal used – lignite, bituminous or anthracite. Most commonly, bituminous coal is used. The tar is further processed, generating fractions of various applications.[14] Coal tar is a black or dark brown liquid or a high-viscosity semi-solid.[15]

Uses

[edit]

Coal tars have the following major uses:

  • production of carbon-based electrodes for aluminium processing
  • source of valuable organic compounds, including naphthalene, phenanthrene, acenaphthene, pyrene, carbazole, quinoline, phenols
  • Wood preservatives
  • resins for paints and coatings.[7]

Chemical products

[edit]

Coal tar is a major source of organic compounds. This application complements the petrochemical industry, which mainly produces alkanes and alkenes. It is a source of polycyclic aromatic hydrocarbons:

Many of these chemicals are precursors to dyes (notably tartrazine/Yellow #5), and photographic materials.[18]

Specialty carbons

[edit]
  • As a source of carbon black.[19]
  • As a binder in manufacturing graphite; a considerable portion of the materials in "green blocks" is coke oven volatiles (COV). During the baking process of the green blocks as a part of commercial graphite production, most of the coal tar binders are vaporised and are generally burned in an incinerator to prevent release into the atmosphere, as COV and coal tar can be injurious to health.[20][21]
  • As a main component of the electrode paste used in electric arc furnaces. Coal tar pitch act as the binder for solid filler that can be either coke or calcined anthracite, forming electrode paste, also widely known as Söderberg electrode paste.[22]
  • As a feed stock for higher-value fractions, such as naphtha, creosote and pitch. In the coal gas era, companies distilled coal tar to separate these out, leading to the discovery of many industrial chemicals.

Construction and combustion

[edit]

Only half of the coal tar is used for chemical production. The remaining ca. 15M tons are used for bulk applications. For example coal tar is incorporated into some parking-lot sealcoat products used to protect the structural integrity of the underlying pavement.[23] Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch.[23] Research[24] shows that it is used throughout the United States of America, but several areas have banned its use in sealcoat products, including the District of Columbia; Austin, Texas; Dane County, Wisconsin; the state of Washington; and several municipalities in Minnesota and others.[25] From 2025, Canada has also banned its use in sealants.[26]

Coal tar is also used in roofing.

Some coal tar is used as fuel for heating or to fire boilers. Like most heavy oils, it must be heated before it will flow easily.[15]

Herbal medicine

[edit]

Topical treatments

[edit]

In rare herbal treatments, coal tar is used to provide relief from various skin disorders, such as dandruff, seborrheic dermatitis or psoriasis.[4][5][27] Coal tar is generally available as a generic medication over the counter for external use only as a shampoo, gel, cream or ointment.[4][5][27] User acceptance of coal tar for these treatments tends to be poor because it is extremely messy, stains skin and hair, and has a foul odor.[4][27]

Although coal tar topical products have been used to treat childhood psoriasis, this is an uncommon clinical practice, with risk of cancer development existing from long-term treatment.[28]

Adverse effects of using topical coal tar may include folliculitis, skin irritation, contact dermatitis, phototoxicity, and changes in skin pigmentation.[4][5][27]

Potential toxicity

[edit]

Use of coal tar on the skin increases the risk of skin cancer.[4][29] Coal tar derivatives are contraindicated for people with the inherited red cell blood disorder glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency), as they can cause oxidative stress leading to red blood cell disruption.[30]

Coal tar is a skin irritant.[4][17]

Cancer

[edit]

Many of constituents of coal tar are polycyclic aromatic hydrocarbons, which can be carcinogenic.[31][32][33]

The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens, indicating a direct cause of cancer.[34]

In response to public health concerns regarding the carcinogenicity of PAHs some municipalities, such as the city of Milwaukee, have banned the use of common coal tar-based road and driveway sealants, citing concerns of elevated PAH content in groundwater.[35]

The residue from the distillation of high-temperature coal tar, primarily a complex mixture of three or more membered condensed ring aromatic hydrocarbons, is a substance of very high concern by the European Chemicals Agency.[36]

Analgesic precursor

[edit]

Some phenolic coal tar derivatives have analgesic (pain-killer) properties. These included acetanilide, phenacetin, and paracetamol.[37][better source needed]

Regulation

[edit]

The U.S. Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit to 0.2 mg/m3 benzene-soluble fraction over an 8-hour workday. The U.S. National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 0.1 mg/m3 cyclohexane-extractable fraction over an 8-hour workday. At levels of 80 mg/m3, coal tar pitch volatiles are immediately dangerous to life and health.[38]

The use of coal tar in cosmetic products was forbidden in the European Union by a directive in 2009.[39]

See also

[edit]

References

[edit]
  1. ↑ Berenblum I (September 1948). "Liquor picis carbonis; a carcinogenic agent". British Medical Journal. 2 (4577): 601. doi:10.1136/bmj.2.4577.601. PMC 2091540. PMID 18882998.
  2. ↑ "ToxFAQs for Creosote". US Centers for Disease Control and Prevention. 8 July 2024. Retrieved 21 September 2025.
  3. ↑ Vallee Y (1998). Gas Phase Reactions in Organic Synthesis. CRC Press. p. 107. ISBN 978-90-5699-081-7.
  4. 1 2 3 4 5 6 7 "Coal tar (Monograph)". Drugs.com. 19 February 2026. Retrieved 5 September 2026.
  5. 1 2 3 4 "Coal tar (topical route)". Mayo Clinic. 1 February 2026. Retrieved 5 September 2026.
  6. ↑ Hornbostel C (1991). Construction Materials: Types, Uses and Applications. John Wiley & Sons. p. 864. ISBN 978-0-471-85145-5. Archived from the original on 18 September 2017.
  7. 1 2 Blümer GP, Collin G, Höke H (2011). "Tar and Pitch". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a26_091.pub2. ISBN 978-3-527-30673-2.
  8. ↑ "History The Early Years (1863–1881)". Bayer AG. Retrieved 4 February 2021.
  9. ↑ "Dyes from Coal Tar Products". Scientific American. 20 February 2024. Retrieved 9 July 2025.
  10. ↑ Sneader W (2005). Drug Discovery: A History. John Wiley & Sons. p. 356. ISBN 978-0-471-89979-2. Archived from the original on 18 September 2017.
  11. ↑ "Coal Tar Oil | OEC".
  12. ↑ Ronalds BF (2019). "Bonnington Chemical Works (1822-1878): Pioneer Coal Tar Company". International Journal for the History of Engineering & Technology. 89 (1–2): 73–91. doi:10.1080/17581206.2020.1787807. S2CID 221115202.
  13. ↑ Smith M. "GANSG – Coal Tar Distillers". Igg.org.uk. Archived from the original on 19 June 2013. Retrieved 8 March 2013.
  14. 1 2 Granda M, Blanco C, Alvarez P, Patrick JW, Menéndez R (2014). "Chemicals from Coal Coking". Chemical Reviews. 114 (3): 1608–1636. Bibcode:2014ChRv..114.1608G. doi:10.1021/cr400256y. hdl:10261/202957. PMID 24080106.
  15. 1 2 Speight JG (2015). "Coal gasification processes for synthetic liquid fuel production". In Luque R, Speight JG (eds.). Gasification for Synthetic Fuel Production. Woodhead Publishing Series in Energy. Woodhead. pp. 201–220 (212). doi:10.1016/B978-0-85709-802-3.00009-6. ISBN 978-0-85709-802-3.
  16. ↑ Betts WD (1997). "Tar and pitch". In John Wiley & Sons, Inc (ed.). Kirk-Othmer Encyclopedia of Chemical Technology (5th ed.). New York: John Wiley & Sons, Inc. doi:10.1002/0471238961. ISBN 978-0-471-23896-6.
  17. 1 2 3 Roberts L (2014). "Coal Tar". In Wexler P (ed.). Encyclopedia of Toxicology (Third ed.). Oxford: Academic Press. pp. 993–995. doi:10.1016/b978-0-12-386454-3.00012-9. ISBN 978-0-12-386455-0. Coal tar is classified as a human carcinogen ... Both inhalation and dermal routes of exposure are considered hazardous.
  18. ↑ Hathaway AW (2011). Remediation of Former Manufactured Gas Plants and Other Coal-Tar Sites. Taylor & Francis Group.
  19. ↑ "Market Study: Carbon Black". Ceresana. Retrieved 26 April 2013.
  20. ↑ "CDC - Immediately Dangerous to Life or Health Concentrations (IDLH): Coal tar pitch volatiles - NIOSH Publications and Products". www.cdc.gov. 2 November 2018. Retrieved 5 October 2021.
  21. ↑ Speight JG (2015). Asphalt materials science and technology. Amsterdam: Elsevier Science. p. 60. ISBN 978-0-12-800501-9. OCLC 922698102.
  22. ↑ Beukes JP, Roos H, Shoko L, Van Zyl PG, Neomagus HW, Strydom CA, et al. (June 2013). "The use of thermomechanical analysis to characterise Söderberg electrode paste raw materials". Minerals Engineering. 46–47: 167–176. Bibcode:2013MiEng..46..167B. doi:10.1016/j.mineng.2013.04.016. ISSN 0892-6875.
  23. 1 2 Mahler BJ, Van Metre PC (2 February 2011). "Coal-Tar-Based Pavement Sealcoat, Polycyclic Aromatic Hydrocarbons (PAHs), and Environmental Health". U.S. Geological Survey Fact Sheet. Archived from the original on 28 March 2013. Retrieved 8 March 2013.
  24. ↑ Van Metre PC, Mahler BJ (December 2010). "Contribution of PAHs from coal-tar pavement sealcoat and other sources to 40 U.S. lakes". The Science of the Total Environment. 409 (2): 334–344. Bibcode:2010ScTEn.409..334V. doi:10.1016/j.scitotenv.2010.08.014. PMID 21112613.
  25. ↑ Mahler BJ, Metre PC, Crane JL, Watts AW, Scoggins M, Williams ES (March 2012). "Coal-tar-based pavement sealcoat and PAHs: implications for the environment, human health, and stormwater management". Environmental Science & Technology. 46 (6): 3039–45. doi:10.1021/es203699x. PMC 3308201. PMID 22296333.
  26. ↑ "Compliance guide for the Certain Products Containing Toxic Substances Regulations". Government of Canada. 25 November 2025.
  27. 1 2 3 4 "Psoriasis treatment: Coal tar". American Association of Dermatology. 2025. Retrieved 21 September 2025.
  28. ↑ Lie E, Choi M, Wang SP, Eichenfield LF (January 2024). "Topical Management of Pediatric Psoriasis: A Review of New Developments and Existing Therapies". Paediatric Drugs. 26 (1): 9–18. doi:10.1007/s40272-023-00592-9. PMC 10769900. PMID 37847480.
  29. ↑ "Coal tar and coal-tar pitch". National Cancer Institute, US National Institutes of Health. 7 August 2024. Retrieved 5 September 2026.
  30. ↑ US EPA National Center for Environmental Assessment (15 March 2009). "Hematologic Disorders". hero.epa.gov. Retrieved 21 April 2020.
  31. ↑ Creosote. US: Agency for Toxic Substances Disease Registry, Division of Toxicology, Dept. of Health and Human Services, Public Health Service. 2002. OCLC 816079578.
  32. ↑ "Public Health Statement for Creosote". Agency for Toxic Substances and Disease Registry. September 2002.
  33. ↑ "EUR-Lex - 32013R1272 - EN - EUR-Lex". eur-lex.europa.eu. Archived from the original on 19 October 2015. Retrieved 10 June 2017. ...are classified as carcinogens of category 1B in accordance with Annex VI to Regulation (EC) No 1272/2008 of the European Parliament
  34. ↑ IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. (2012). "Chemical Agents and Related Occupations.". Coal-Tar Pitch. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Lyon (FR): International Agency for Research on Cancer.
  35. ↑ Quirmbach C (7 February 2017). "Milwaukee Common Council Bans Coal Tar Sealants". Wisconsin Public Radio.
  36. ↑ "Candidate List of substances of very high concern for Authorisation". European Chemicals Agency. 2026. Retrieved 5 September 2026.
  37. ↑ Brown T, Dronsfield A, Ellis P (30 June 2005). "Pain relief: from coal tar to paracetamol". Education in Chemistry. Vol. 42, no. 4. Royal Society of Chemistry. pp. 102–105. Archived from the original on 13 October 2017. Retrieved 14 June 2018.
  38. ↑ "CDC – NIOSH Pocket Guide to Chemical Hazards – Coal tar pitch volatiles". cdc.gov. Archived from the original on 8 December 2015. Retrieved 27 November 2015.
  39. ↑ "Consolidated TEXT: 32009R1223 — EN — 01.09.2025". eur-lex.europa.eu. Retrieved 6 September 2026.
[edit]
Retrieved from "https://en.wikipedia.org/w/index.php?title=Coal_tar&oldid=1380351734"