コールタール

化学的特性Coal tars are by-products of the destructive distillation (carbonization) of coal to produce coke or gas. The composition and properties of a coal tar depend primarily on the temperature of the carbonization and to a lesser extent on the nature (source) of the coal used as feedstock. In general, coal tars are complex combinations of hydrocarbons, phenols, and heterocyclic oxygen, sulfur, and nitrogen compounds. Over 400 compounds have been identified in coal tars, and as many as 10,000 may actually be present. The PAH content of coal tars increases with increasing carbonization temperature. Coal tars typically are black or almost-black viscous liquids or semisolids with a characteristic naphthalene-like odor (ATSDR 2002). They are slightly soluble in water, partially soluble in acetone, carbon disulfide, chloroform, diethyl ether, ethanol, methanol, petroleum ether, and sodium hydroxide, and soluble in benzene and nitrobenzene. Lowtemperature coal tars (formed at temperatures below 700°C) are black, viscous liquids that are denser than water and contain a lower percentage (40% to 50%) of aromatic compounds than high-temperature coal tars (IARC 1985). Coal tars are highly flammable and corrosive, and toxic gases may be released when they burn. Their vapors can form explosive mixtures with air (HSDB 2009). Coal-tar pitches are shiny, dark-brown to black residues produced during the distillation of coal tars. They contain various PAHs, their methyl and polymethyl derivatives, and heteronuclear compounds (IARC 1985).

解説タール（油状物質），有機物の熱分解によって生成する褐色から黒色の粘稠(ねんちゅう)性油状物質の総称。木(もく)タール、石油ピッチなどがあるが、狭義には石炭の乾留で得られるコールタールをさす。タールの組成・性状は原料により異なるが、多環縮合芳香族化合物を基本とし、これに少量の硫黄(いおう)、窒素、酸素、灰分などを含む。防腐剤、塗料などに用いられるが、もっとも重要なのは芳香族系化学原料としての用途で、石炭化学工業はコールタールから、有用な化学物質を得ることを出発点として発展した。

用途コールタール=タール製品原料、防錆塗料、漁網染料、油煙、燃料

説明Coal tar is a complex hydrocarbon mixture produced by thermal destruction (pyrolysis) of coal, typically a dark viscous liquid or semisolid with a smoky or naphthenic odor. The composition of coal tar will be influenced by the process used for pyrolytic distillation as well as by the original composition of the coal; however all coal tars will be comprised of a variable mixture of organic compounds including benzene, toluene, xylenes, cumenes, coumarone, indene, benzofuran, naphthalene, acenaphthene, methylnaphthalenes, fluorine, phenol, cresols, pyridine, picolines, phenanthracene, carbazole, quinolines, fluoranthene, and pyrene. The number of specific chemical constituents is in the thousands. Coal tar creosotes and coal tar distillates, oily liquids generally lighter in color and of lower viscosity than coal tar, are fractions produced by additional distillation of crude coal tar. Coal tar pitch is a highly viscous dark semisolid byproduct of coal pyrolysis. Coal tar volatiles are the vapors produced from heated coal tar or coal tar pitch, containing lower molecular weight (smaller ring number) polycyclic aromatic hydrocarbons (PAHs). Coal tar is noteworthy as one of the first – if not the first – chemical substances documented to cause cancer through occupational exposures. In the eighteenth century, Sir Percival Pott, a British surgeon, noticed a higher incidence of cancers in chimney sweeps chronically exposed to soot and coal tar. He then demonstrated excess cancers occurring in laboratory animals when coal tar is applied to the ears and skin. In the early twentieth century, polycyclic aromatic compounds isolated from coal tar were identified as chemical carcinogens.

使用Coal tars and coal-tar pitches have many uses in industry and in consumer products. Coal tars are used primarily for the production of refined chemicals and coal-tar products, such as creosote, coal-tar pitch, and crude naphthalene and anthracene oils from the distillation of crude coal tar. Coal tar has been used as a fuel in open-hearth furnaces and blast furnaces in the steel industry, as a binder and filler in surface-coating formulations, and as a modifier for epoxy-resin surface coatings. U.S. Pharmacopeia–grade coal tar is approved for use in denatured alcohol (IARC 1985). Coal-tar preparations have been used for many years to treat various skin conditions, such as eczema, psoriasis, seborrheic dermatitis, and dandruff. Both prescription and nonprescription preparations are available and include cleansing bars, creams, gels, lotions, ointments, shampoos, and other topical solutions and suspensions (DermNet NZ 2010). Coal tar is also registered as an active ingredient in pesticides with the U.S. Environmental Protection Agency (EPA 2003). Coal-tar pitches are used primarily as the binder for aluminumsmelting electrodes (IARC 1984). They are also used in roofing materials, to impregnate and strengthen refractory brick (for lining industrial furnaces), and in surface coatings, such as pipe-coating enamels and black varnishes used as protective coatings for industrial steelwork and as antifouling paints for boats. Hard pitch is used as a binder for foundry cores. Coke-oven pitch is used to produce pitch coke, which is used as the carbon component of electrodes, carbon brushes, and carbon and graphite articles. Distillation fractions and residues from high-temperature coal tars are used for road paving and construction and in the production of naphthalene, recovery of benzene, production of anthracene paste, briquetting of smokeless solid fuel, impregnation of electrodes and fibers, and manufacture of electrodes and graphite (IARC 1985).

使用用途コールタールの主な使用用途は、タール分留製品原料、防錆塗料、漁網染料、油煙、燃料です。かつては枕木や木電柱などの木材の防腐剤や、トタン屋根の塗料として広く用いられていましたが、近年では建材の移り変わりやコンクリート製の普及により、使用されることが少なくなっています。炭素電極の支持材にも使用されていました。 また、コールタール製剤には角質溶解・形成作用、止痒作用があるため、かつては医療にも用いられていた物質です。特に、皮膚疾患の1種である乾癬では、かつてはコールタールを外用するゲッケルマン療法が行われていました。しかし、後述する発癌性が指摘されてからは行われなくなってきています。