Tar (of Middle Low German ter "tar, resin" related to germanic treva , terva "tree Kienholz"; latin pix , resulting pitch ) is a brownish to black, viscous mixture of organic compounds obtained by decomposing thermal treatment ( pyrolysis of organic) Natural Products is won. Another term for tar, which goes back to the Spanish "Alquitrán" or the Arabic word al-quitrán , is Goudron (the French word for tar), for example in "Goudronanstrich".
Products that remain in the sump as a residue when the more volatile components ( gasoline , kerosene , heavy oil , etc.) are removed from the distillation of petroleum are called bitumen . Bitumen and tar are two distinctly different substances , even if they are both brown-black and thick.
The word, which was adopted from Low German into High German in the 16th century, goes back to Middle Low German ter [e] (→ English tar ). The residents of the coasts of North and Baltic Sea (for the tar an indispensable aid in the shipbuilding was) common word actually means "the tree Related" and belongs to Indo deru- "oak tree" (→ English. Tree ) from which the Germanic tree name suffix -đr [a] -der or -ter (for example in lilac , elder , juniper ) goes back.
Tar can come from various organic compounds:
- Lignite tar is a brown to black-brown, solid mass. It is the most important product in the smoldering of lignite or lignite briquettes . The amount and composition of the lignite tar depends on the initial coal and the type of carbonization. While “heating surface smoldering” leads to smaller tar yields and specifically heavier tars, “flushing gas smoldering” results in a significantly larger tar yield. The flushing gas is characterized by a high alkane content ( paraffins ). Depending on the decomposition temperatures, a distinction is made between lignite smoldering tar (lignite tar), which is obtained at smoldering temperatures of 550 to 650 ° C, and lignite high-temperature tar (BHT tar), which is obtained at coking temperatures of 1000 to 1200 ° C. The main product at these temperatures is high- temperature lignite coke (coking). In contrast to the coal tar, which mainly contains aromatic compounds , the lignite tar consists mainly of aliphatic hydrocarbons .
- Oil tar results from the thermal decomposition of mineral oils to oil gas and from the production of water gas . It is similar in texture and composition to coal tar, but differs from it in its lower density and lower viscosity . Furthermore, it hardly contains any phenols or basic substances. Oil tar is often used as fuel or to run diesel engines .
- Shale tar is a dark brown liquid that is created when oil shale swells and is mainly processed to produce lubricating and diesel oil .
- Wassergasteer is a dark brown, oily-liquid mass with a high water content. It arises during the production of water gas or generator gas and contains mainly aliphatic hydrocarbons and aromatic decomposition products.
- Torfteer is a highly viscous, often at room temperature, unctuous , black liquid from penetrating sharp odor, in addition to phenols saturated and unsaturated aliphatic and aromatic hydrocarbons, pyridine bases, sulfur compounds, and fatty acids contains.
- Fat tar is a brown, viscous mass that results from the fractional distillation of waste fats (bone fat , wool fat , skin fat, covering fat , sewage fat and milled fat ), fats and fatty oils. It is broken down again into various fatty acids by distillation. The tough, after cooling, quite hard blister residue is called stearin - or fat pitch. This is used for the insulation of cables .
- Bone tar (deer horn oil, animal oil) is produced by the charring of defatted, often still crushed bones ( animal charcoal ) as a black-brown, thick liquid with an unpleasant smell, from which Dippels oil is obtained by distillation . The distillation residue is bone tar pitch.
- Biomass tar is a black-brown, viscous mass that is created in biomass gasification when the gas produced is cooled. It can be used for various purposes.
- Planting tar produced during the carbonization of vegetable charcoal or other plant materials such. B. leaves, grain bowls , gerberlohe , etc.
- Vine tar is produced as a sedimentation residue from wood vinegar (slate tar, lignin tar) or after its evaporation in a two-bubble system.
- Other tars: Melasseteer , Schlempeteer , Bagasseteer , Vinasseteer u. a .; they arise from the pyrolysis of molasses , bagasse , vinasse and stillage .
- Mondgasteer originated from the production of lunar gas .
Coal tar oil is still of certain importance for industrial wood protection, e.g. B. for railway sleepers or overhead line masts . It has been further developed in recent years to improve its environmental impact.
The Swiss doctor Ernest Guglielminetti developed a forerunner method for today's asphalting roads. To combat dust , he had 40 meters of road coated with hot tar for the first time on March 13, 1902 in Monaco. This procedure found worldwide distribution and Guglielminetti was nicknamed Dr. Goudron (French for "tar"). Contrary to its common usage (" taring " as a term for asphalt work on roads), tar has been banned in West Germany since 1984 and in East Germany since 1990 because of its harmful effects on public roads and paths . Instead, bitumen is used as a binding agent today . In some cases so-called carbobitumen (also pitch bitumen) was used. It is a mixture of bitumen and tar. Like pure tar, this mixed form is no longer used in Germany and must be disposed of separately.
Long-term exposure of the tar to the skin can cause skin changes which, in the worst case, can cause cancer . Tar preparations are also used in medicine as externally applicable drugs against skin diseases , as they relieve itching , kill germs and promote blood circulation .
As a building material, tar is particularly harmful to health when processed. When in contact with water, polycyclic aromatic hydrocarbons (PAH) can get into the groundwater. Therefore, the use of tar in Germany in public road construction is no longer allowed under the aspects of occupational , soil and water protection . If old layers that are suspected of containing tar are to be broken up during road construction work, rapid tests with UV light or sprays, for example with silver iodide , can be used. If the test result is positive, samples are taken for further analysis and the PAH value is determined in the laboratory in accordance with DIN ISO 18287. The result of this investigation determines the possible further use or disposal. Only slightly contaminated material may be reused in different ways, depending on the degree of exposure, for example in cold recycling . In order to finally remove the tar contaminated sites from the recycling cycle, no tar-containing recycling building materials have been permitted on federal trunk roads since January 2018 . Many countries have issued similar requirements.
- Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 6: T – Z , 8th edition, Franckh, Stuttgart 1988, ISBN 3-440-04516-1 , p. 4137.
- The dictionary of origin (= Der Duden in twelve volumes . Volume 7 ). Reprint of the 2nd edition. Dudenverlag, Mannheim 1997, p. 849 . See also Friedrich Kluge : Etymological dictionary of the German language . 7th edition. Trübner, Strasbourg 1910 ( p. 457 ).
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