Coal tar production

The discovery that usehil chemicals could be made from coal tar provided the foundation upon which the modem chemical industry is built. Industrial chemistry expanded rapidly in the late nineteenth century in German laboratories and factories where coal-tar chemicals were refined and used in synthesis of dyes and pharmaceuticals. But coal-tar production has an eadier origin, dating back to the discovery by William Murdock in 1792 that heating coal in the absence of air generated a gas suitable for lighting. Murdock commercialized this technology, and by 1812 the streets of London were illuminated with coal gas (1). 

Large-scale recovery of light oil was commercialized in England, Germany, and the United States toward the end of the nineteenth century (151). Industrial coal-tar production dates from the earliest operation of coal-gas faciUties. The principal bulk commodities derived from coal tar are wood-preserving oils, road tars, industrial pitches, and coke. Naphthalene is obtained from tar oils by crystallization, tar acids are derived by extraction of tar oils with caustic, and tar bases by extraction with sulfuric acid. Coal tars generally contain less than 1% benzene and toluene, and may contain up to 1% xylene. The total U.S. production of BTX from coke-oven operations is insignificant compared to petroleum product consumptions. 

Pjridine Bases. Formerly, pyridine bases were recovered from coal-tar light oils (18), but in more recent years synthetic pyridine and methylpyridine have mostiy replaced the coal-tar products. 

The risk of skin cancer by contact with pitch dust has in more recent years been reduced by the transport and handling of pitch as a Hquid or as dust-free flakes or pencils. Nevertheless, in handling coal-tar products, certain precautions should be taken. These have become obligatory in tar distilleries and plants using pitch or creosote. 

Coal gas for illumination—and later for heating— was produced by the destructive distillation of coal and resulted in the production of large volumes of tar. This is used in the form of creosote for wood preservation, so that both gasworks sites and impregnation facilities became heavily contaminated with coal tar products. The range of compounds involved is enormous, but attention... 

Topical therapy is the initial drug treatment strategy for patients with mild to moderate psoriasis. It is estimated that approximately 70% to 80% of all patients with psoriasis can he treated adequately with use of topical therapy.1 Topical therapies include corticosteroids, coal tar products, anthralin, vitamin D3 analogues such as calcipotriol, retinoids such as tazarotene, and topical immunomodulators such as tacrolimus and pime-crolimus.18 Vitamin D3 analogues and topical retinoids all affect keratinocyte functions and the immune response. Currently, these are in wider use than is either anthralin or coal tar preparations. 

Coal tar is keratolytic and may have anti-proliferative and anti-inflammatory effects.2 Coal tar products include crude coal tar and tar distillates (liquor carbonis detergens) available as ointments, creams, and shampoos in various strengths. Preparations containing coal tar may precipitate folliculitis,10 will stain clothing, and have an unpleasant odor. They are also photosensitizing and can be combined with UVB phototherapy (Goekermann s regimen) to increase treatment response.19,20... 

The development of the chemical industry did not, of course, spring wholly from the work of theoreticians such as Kekule. William Henry Perkin (1838-1907), working at the age of 18 in the laboratory of August Wilhelm von Hofmann at the Royal College of Science in London, had been put to work on the synthesis of the drug quinine from aniline, the latter a coal-tar product that had been isolated by Hofmann. Perkin failed to synthesize quinine, but as a result of his... 

Certain industrial populations exposed to coal tar products have a demonstrated risk of skin cancer. Substances containing polycyclic hydrocarbons or polynuclear aromatics (PNAs), which may produce skin cancer, also produce contact dermatitis (e.g., coal tar pitch, cutting oils)." Although allergic dermatitis is readily induced by PNAs in guinea pigs, it only rarely is reported in humans from occupational contact with PNAs. Incidences in humans have resulted largely from the therapeutic use of coal tar preparations. ... 

National Institute for Occupational Safety and Health Criteria for a Recommended Standard... Occupational Exposure to Coal Tar Products. DHEW (NIOSH) Pub No 78-107. Washington, DC, US Government Printing Office, 1977... 

Resorcinol may be released to the environment in waste effluents associated with coal gasification and conversion, coal-tar production and shale oil processing and from the combustion of wood and tobacco. It has been detected in low levels in groundwater samples (United States National Library of Medicine, 1997). 

Since metallurgical coke for use in blast furnaces is the prime product of coal carbonization, coal tar production is tied closely io the demand for... 

Cresol, Cresylic Acid or Methylphenol (called Kresol or Oxytoluol in Ger), CH3.CgH4.OH mw 108.13, 0 14.79% A coml coal tar product of the middle heavy oil fractions. It contains a mixt of o-, m- p- isomers which may be separated by fractional distillation into two fractions o- and a mixt of m- p-cresols. The props of cresol depend upon the compn proportion of isomers in the mixt. See Kirk Othmer (Ref 5) for more details o Cresol, wh crysts, phenol-like odor, poisonous, mp 30.8°, bp 191°, d 1.048 at 20° sol in ale, eth chlf si sol in w (Refs 1 7). Prepn other props are given in Beil (Ref 1)... 

Other drugs that change the color of the urine act as follows. Logwood (hematoxylon) does not color acid urine but produces a reddish or violet color in alkaline urine. Santonin imparts a yellowish color to acid urine, with a yellow foam if the urine is made alkaline, it imparts a very pronounced pink color. Picric acid gives reddish-brown color in both acid and alkaline urine. The various coal-tar products give a brownish-black color. Methylene blue imparts a green color. 

Results When you heated the coal, it gave off the gases, mainly methane (CH J and ethane (C2H6), that were trapped in it as it was formed in the earth. This gaseous mixture burned with a characteristic blue flame. The material which remained in the test tube is a form of carbon called coke. If there was any sticky brownish substance there, too, it was a combination of coal tar products, which are the residue of coal burned in this way. 

In the early part of this century, coal and coal tar products were the main source of bulk chemicals. Acetylene was the major feedstock, obtained by converting coal to calcium carbide followed by hydrolysis. As the petroleum and natural gas industries developed, ethylene and other products obtained by cracking hydrocar-... 

A consequence of this is that fresh coal falling on top of the hot coals undergoes pyrolysis and emits coal gas products - hydrogen, methane, ethylene, light and heavy hydrocarbons and coal tar products - which contaminate the synthesis gas. 

These other products represent carbon lost to products other than synthesis gas. They have to be extracted downstream and disposed of In the other hydrocarbons category are coal tar products - phenol and cresols - and can be extracted and sold as by-product. Otherwise the byproducts need to be separated and burned to produce electricity. 

CONSENSUS REPORTS lARC Cancer Review Group 1 IMEMDT 7,174,87 Animal Sufficient Evidence, Human Sufficient Evidence IMEMDT 35,83,85 Human Sufficient Evidence IMEMDT 3,22,73. Reported in EPA TSCA Inventory. OSHA PEL TWA 0.2 mg/mL Carcinogen ACGIH TLV TWA 0.2 mg/m (volatile). Confirmed Human Carcinogen NIOSH REL (Coal Tar Products) TWA 0.1 mg/m3 CHE fraction DOT CLASSIFICATION 3 Label Flammable Liquid... 

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