Coal tar

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Rütgers Chemicals : Plant for hard coal tar distillation

Coal tar ( English coal tar ; as a drug Pix lithanthracis ) is a by-product of coke production ( coke tar) from coal . The viscous black mass, which gives off a characteristic odor (like bitumen ), is obtained from the gases produced in the coking plant . The tar owes its color mainly to suspended free hydrocarbons (depends on the production method) and dark, high-molecular hydrocarbons. Coal tar consists of several thousand, mostly aromatic , compounds, u. a. Hydrocarbons , nitrogenous bases and acids ( phenols ), most of which only occur in tiny percentage fractions. In 1820, naphthalene was the first to be isolated.

history

Since its discovery by Johann Rudolph Glauber in 1658, coal degassing has developed into an important technical process in hard coal coking. Coal tar was initially a waste product in the production of luminous gas , but then found particular interest in the 19th century in connection with the synthesis of organic dyes from its ingredients. Scientists such as Friedlieb Ferdinand Runge , August Wilhelm Hofmann and William Henry Perkin laid the foundations for the tar paint industry , with names such as paint works by Meister, Lucius and Brüning in Höchst , paint factory by Fr. Bayer & Co. in Elberfeld and Badische anilin and Sodafabrik in Ludwigshafen was connected. Until 1850, tar was an annoying by-product of the gas works , which was used as fuel, as a paint for wood and stone, and for the production of soot. Due to the demand for heavy oils for impregnating railway sleepers and pit timber and as a raw material for the production of artificial tar colors, it became a coveted trade item. At the end of the 19th century, coal tar was considered to be the main source of raw materials for the up-and-coming organic-chemical industry because of its high content of aromatic compounds . However, since the yields are only low (50 kg per ton of hard coal) and the demand rose steadily, the coal industry was replaced by petrochemicals in the middle of the 20th century .

Manufacturing

The coal tars are created from gases that are produced during pyrolysis (dry distillation, degassing), coking and carbonization of coal. The gases are cooled by ammonia water (to 80-100 ° C), whereby part (60-70%) of the coal tar condenses. The watery-tarry condensate flows together with the sprinkling liquid into the Dicker separator , where the Dicker sludge , which contains coal and coke dust, is deposited (this is fed back into the feed coal ). At the top, the condensate water and water-containing tar are drawn off from the separator and fed to the condensate separator. The gas leaving the gas collecting line is further cooled in the second stage in the gas pre-coolers (to 20 ° C) and the remaining tar water is precipitated, which is then also fed to the condensate separator .

If hard coal is heated in closed vessels above 600 ° C in the absence of air, the coal decomposes into the following products:

Tars are divided into:

  • Tieftemperaturteere (Schwelteere, Urteere) formed during the carbonization of coal at temperatures up to 600 ° C. In a thin layer, the smoldering tar is a dark brown, transparent oil with a smell of carbon disulphide. Depending on the smoldering process, a distinction is made between heating surface tars (smoldering ovens with indirect, external heat supply) and flushing gas tears (smoldering ovens with direct, internal heat supply). Heating and fuel oils (oil-like fuel for diesel engines) can be obtained from them by distillation, and high-quality diesel oils and carburetor fuels can be obtained by hydrogenation .
  • Medium-temperature tars are produced during coking at 800 ° C. They are already largely cracked and are therefore already very similar to high-temperature tars, from which they differ, however, in having a higher content of benzene , phenol and homologues and a lower pitch content.

However, these two methods are of little importance.

  • High temperature tars are the most important group for technical processing. They are oily to viscous, dark brown to black, shiny liquids with a creosote-like odor. High-temperature tars are formed when the coal is coked at temperatures above 1000 ° C, and their formation can be explained by strong secondary decomposition of the primary tar that is primarily split off . The amount of tar that arises during coking fluctuates between 3 and 4%, based on dry coal, depending on the type of coal. These tars contain more aromatics, more gas and less tar are produced. As the oxygen content of the coal increases, so does the tar yield.

processing

composition

Source:

ingredients

connection average salary (%)
Hydrocarbons
naphthalene 10
Phenanthrene 4.5
Fluoranthene 3
Pyrene 2
Acenaphthylene 2.5
Fluorene 1.8
Chryses 1
Anthracene 1.3
In the 1
2-methylnaphthalene 1.5
1-methylnaphthalene 0.7
Diphenyl 0.4
Acenaphthene 0.2
Heterocycles
Carbazole 0.9
Diphenylene oxide 1.3
Acridine 0.1
Quinoline 0.3
Diphenylene sulfide 0.4
Thionaphthene 0.3
Isoquinoline 0.1
Quinaldin 0.1
Phenanthridine 0.1
7,8-benzoquinoline 0.2
2,3-benzodiphenylene oxide 0.2
Indole 0.2
Pyridine 0.03
2-methylpyridine 0.02
Phenols
phenol 0.5
m -Cresol 0.4
o -Cresol 0.2
p -cresol 0.2
3,5-dimethylphenol 0.1
2,4-dimethylphenol 0.1

Typical characteristics

density 1.175 g cm −3
water 2.5%
Toluene insolubles 5.50%
Quinoline insolubles 2.0%
Coking residue (according to Muck ) 14.6%
Carbon (waf) 91.39%
Hydrogen (waf) 5.25%
Nitrogen (waf) 0.86%
Oxygen (waf) 1.75%
sulfur 0.75%
chlorine 0.03%
ash 0.15%
zinc 0.04%
naphthalene 10.0%
Boiling analysis (DIN 1995):
up to 180 ° C water 2.5%
Light oil 0.9%
Boiling point 180-230 ° C 7.5%
Boiling section 230-270 ° C 9.8%
Boiling section 270-300 ° C 4.3%
Boiling section 300 ° C to pitch 20.1%
bad luck 54.5%
Loss of distillation 0.5%

use

Naphtha and solvent naphtha are made from coal tar , as well as creosote and carbolineum as wood preservatives (e.g. for railway sleepers and roofing felt ). It used to be the starting material for the production of various chemical substances, including tar dyes and phenol and phenol derivatives such as cresols and xylenols , these are still largely obtained from coal tar today.

Large amounts of aromatics (naphthalene, anthracene, indene, coumarone ), heterocycles (carbazole, indole, quinoline, pyridine), phenols (phenol, xylenol, cresol) and resins are obtained. A significant amount of soot is also obtained from tar oils.

Purified extracts from coal tar can be used for the treatment of psoriasis (e.g. psoriasis vulgaris ), chronic eczema and neurodermatitis, but in Germany they are banned as an ingredient in cosmetics because of their carcinogenic properties ; this prohibition does not apply to formulations based on a doctor's prescription. Since coal tar is difficult to process due to its high viscosity , a 20% solution of coal tar in soap alcohol, referred to as Liquor Carbonis detergent according to the DAC , is used . Coal tar inhibits itching ( antipruriginosum ) and has a bactericidal , fungicidal and insecticidal effect due to its ingredients, such as cresols .

A synthetic graphite can be obtained from the pitch contained in coal tar through thermal treatment , which is used as an electrode material for the electrochemical production of aluminum , for the production of electrical steel , in chlor-alkali electrolysis and for carbon fibers .

hazards

safety instructions
CAS number
  • 8007-45-2
  • 65996-93-2
EC number

266-028-2

ECHA InfoCard

100.060.007

GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
08 - Dangerous to health 09 - Dangerous for the environment

danger

H and P phrases H: 350-340-360FD-410
P: ?
Authorization procedure under REACH

particularly worrying : carcinogenic ( CMR ), persistent, bioaccumulative and toxic ( PBT ), very persistent and very bioaccumulative ( vPvB )

Toxicological data
  • 0.9 mg l −1 ( LC 50fish , 96 hours , median value)
  • 0.11 mg l −1 ( EC 50crustaceans , 48 hours , median value)

Coal tar contains various substances, some of which are toxic, carcinogenic, or harmful to the environment. For these reasons, the manufacture, use and placing on the market in Germany have been severely restricted since 1991 by the Tar Oil Ordinance and made punishable under exceptional circumstances; Since 2009, there have been bans in the European Union for tar oils and tar oil-treated woods, which have direct effect in the member states.

See also

literature

Web links

Individual evidence

  1. ^ W. Bleyberg, G. Meyerheim, W. Bachmann, J. Davidsohn, F. Frank, F. Fritz, J. Herzenberg, L. Jablonski, H. Kantorowicz, HP Kaufmann, EL Lederer, P. Levy, I. Lifschütz , H. Lindemann, H. Mallison: Hydrocarbon oils and fats: as well as the chemically and technically related substances. 7th edition, Springer-Verlag, 1933, ISBN 978-3-642-89045-1 , p. 555.
  2. AW Hofmann: Chemical investigation of the organic bases in coal tar oil. In: Liebigs Ann . 47, pp. 37-87, 1843.
  3. ^ H. Winter: Thermal theory and chemistry: for coking and mine officials. Springer-Verlag, 1922, ISBN 978-3-642-98135-7 , p. 102.
  4. ^ Andreas von Usedom: Organic chemistry, biochemistry, chemical industry. Mentor, 2003, ISBN 978-3-580-64134-4 , p. 50.
  5. Schwelung on Spektrum.de. accessed on August 4, 2016.
  6. Manfred Baerns, Arno Behr, Axel Brehm, Jürgen Gmehling, Kai-Olaf Hinrichsen, Hanns Hofmann, Ulfert Onken, Regina Palkovits, Albert Renken: Technische Chemie. John Wiley & Sons, 2013, ISBN 978-3-527-67409-1 , p. 531.
  7. ^ Heinz-Gerhard Franck, Gerd Collin: coal tar: chemistry, technology and use. Springer-Verlag, 1968, ISBN 978-3-642-88258-6 .
  8. Walter Fuchs : Investigations into the composition and usability of smoldering tar fractions. In: Research reports from the North Rhine-Westphalia Ministry of Economics and Transport. Westdeutscher Verlag, 1952, ISBN 978-3-663-03223-6 .
  9. Tar on Spektrum.de, accessed on August 4, 2016.
  10. ^ Heinz-Gerhard Franck, Jürgen W. Stadelhofer: Industrial Aromatic Chemistry: Raw Materials · Processes · Products . Springer, 1987, ISBN 978-3-662-07875-4 , urn : nbn: de: 1111-201301221589 (Table 3.1 and Table 3.3).
  11. C. Zerbe: Mineral oils and related products: A manual for laboratory and operation. Second part, 2nd edition, Springer, 1969, ISBN 978-3-642-87510-6 , p. 482 f.
  12. waf = water and ash free
  13. Softening point (KS) 67 ° C.
  14. Entry on pitch, coal tar, high temperature in the GESTIS substance database of the IFA , accessed on August 27, 2016(JavaScript required) .
  15. Entry on Pitch, coal tar, high-temp. in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on August 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  16. Entry in the SVHC list of the European Chemicals Agency , accessed on August 17, 2014.
  17. a b Entry for CAS no. 65996-93-2 in the GESTIS substance database of the IFA , accessed on August 17, 2014(JavaScript required) .
  18. Article 67 of Regulation (EC) No. 1907/2006 of the European Parliament (so-called REACH-VO) with its Annex XVII, entry 31 for the substances listed there in column 1