Coal tar is denser than water and is the condensation product obtained by cooling, to approximately ambient temperature, the gas evolved in the high-temperature (greater than 700Cor 1292F) destructive distillation of coal to produce coke in the steel industry. The coke oven plant is the principal source of coal tar. The hot gases and vapors produced during the conversion of coal to coke are collected by a scrubber that condenses the effluent into ammonia, water, crude tar, and other by-products. Crude tar is separated from the remainder of the condensate for refining and may undergo further processing. The composition and properties of a coal tar depend mainly on the temperature of the carbonization and, to a lesser extent, on the nature of the coal used as feedstock. It is composed primarily of a complex mixture of aromatic hydrocarbons, and it may contain minor amounts of phenolic compounds and aromatic nitrogen bases. Coal tar is a nearly black, viscous liquid,or semisolid that has characteristic, “naphthalene-like” odor. Purified coal tar is a light yellow, thin, oily liquid. It is complex mixture containing thousands of chemicals. Generally, it is 2–8% light oils (benzene, toluene, and xylene), 8–10% middle oils (chiefly phenols, cresols, and naphthalene), 8–10% heavy oils (naphthalene and derivatives), 16–20% anthracene oils (mostly anthracene), and 50% pitch. Part of coal tar can dissolve in water, and nearly all dissolves in benzene or nitrobenzene; it is miscible with absolute alcohol, acetone, petrolatum, oils, and fats.
The majority (88%) of crude coal tars produced in the United States are distilled into refined chemicals and bulk products. Coal tar is used as a raw material for plastics, solvents, dyes, drugs, paints, roofing, insulation, pesticides, sealants, road surfaces, roofing, pipe coating, and waterproofing materials. It is also used as a denaturant for alcohol and fuel. Coal tar pharmaceutical preparations continue to be used as keratoplastic, antipruritic, and antifungal agents for treating dandruff, psoriasis, and eczema. Some (11%) is burned as fuel in the steel industry in open hearth furnaces and blast furnaces because of its availability, its low sulfur content, and its high heating value.
Coal tar is also the source of other toxic chemicals, including 1-pentene, cyclohexene, benzene, toluene, xylene, naphthalene, anthracene, phenanthrene, benz[a]anthracene, chrysene, 1,7-dimethylchrysene, dibenz[a,h]anthracene, trimethylbenzenes, phenol, creosote, pyrrole, pyridine, methyl mercaptan, and ethyl mercaptan.
The condensation product obtained by cooling, to approximately ambient temperature, the gas evolved in the high temperature (greater than 700.degree.C (1292.degree.F)) destructive distillation of coal. A black viscous liquid denser than water. Composed primarily of a complex mixture of condensed ring aromatic hydrocarbons. May contain minor amounts of phenolic compounds and aromatic nitrogen bases.
