coal tar

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coal tar,

product of the destructive distillation of bituminous coal. Coal tar can be distilled into many fractions to yield a number of useful organic products, including benzene, toluene, xylene, naphthalene, anthracene, and phenanthrene. These substances, called the coal-tar crudes, form the starting point for the synthesis of numerous products—notably dyes, drugs, explosives, flavorings, perfumes, preservatives, synthetic resins, and paints and stains. The residual pitch left from the fractional distillation is used for paving, roofing, waterproofing, and insulation.

Coal Tar

 

one of the products of coal coking; a viscous black liquid with a characteristic phenol odor, a density of 1, 120–, 250 kg per cu m, and a yield of ~ 3 percent of the coal bulk after coking. Coal tar was originally (in the first half of the 19th century) a waste product of gas production. Numerous aromatic hydrocarbons and their derivatives were later discovered in coal tar and have been used since the second half of the 19th century as raw material in the synthesis of dyes, medicines, and other products.

Coal tar is a complex mixture of heterocyclic aromatic compounds and their derivatives. These compounds boil off over a broad range of temperatures (see Table 1). The composition of coal tar from different plants is uniform, depending less on the coal composition than on the coking conditions. More than 400 individual compounds have been extracted from coal tar, and some of them are produced on an industrial scale. The primary processing of coal tar is carried out at coke by-product plants. The tar is distilled in units that include a tube furnace for heating and evaporation and rectifying columns for separating the distillate into fractions. The individual substances are extracted from the coal tar fractions (see Table 1) either by crystallization or by treatment with reagents (for example, an alkali solution in the extraction of phenols). Among the residues left after extraction are process oils, which are used as the absorbers of benzene products from coking gas, for preserving wood, and in producing lamp black. Pitch (the residue after separating the coal tar into fractions) is used for manufacturing electrode coke and coatings. Coal tar production in the USSR has been growing steadily; the USSR has the highest output and the most complete processing of coal tar in the world.

REFERENCES

Koliandr, L. Ia. Ulavlivanie ipererabotka khimicheskikh produktov kok sovaniia, 2nd ed. Kharkov, 1962.
Litvinenko, M. S., and I. M. Nosalevich. Khimicheskie produkty kok >sovaniia dlia proizvodstva polimernykh materialov. Kharkov, 1962.

D. D. ZYKOV

coal tar

[′kōl ‚tär]
(materials)
A tar obtained from carbonization of coal, usually in coke ovens or retorts, containing several hundred organic chemicals.

coal tar

a black tar, produced by the distillation of bituminous coal, that can be further distilled to yield benzene, toluene, xylene, anthracene, phenol, etc.