Coal-tar industries

Chromates and dichromates are used in industry as oxidising agents, for example in the coal tar industry, in the leather industry (chrome taiming), and in the dye industry as mordants. Some chromates are used as pigments, for example those of zinc and lead. Chromates and dichromates are poisonous. 

Other Organic Processes. Solvent extraction has found appHcation in the coal-tar industry for many years, as for example in the recovery of phenols from coal-tar distillates by washing with caustic soda solution. Solvent extraction of fatty and resimic acid from tall oil has been reported (250). Dissociation extraction is used to separate y -cresol fromT -cresol (251) and 2,4-x5lenol from 2,5-x5lenol (252). Solvent extraction can play a role in the direct manufacture of chemicals from coal (253) (see Eeedstocks, coal chemicals). 

In 1980, the last year for which a breakdown has been pubUshed, the amount of benzene derived from coal in the United States was 168,000 t or 2.5% of domestic benzene production. Coal-derived toluene was 0.8% of production, and xylenes from coal were only 0.1% of total chemical production (9). The amounts and proportions of BTX components derived from coal in the United States are expected to be nearly the same today as in 1980. Based on information submitted to the International Trade Commission, approximately 25 companies participated in the coal-tar industry in the United States in 1990. 

In the latter part of the nineteenth century, workers in the paraffin refining, shale oil, and coal tar industries had high incidences of skin cancer. A possible cause emerged during the period 1915-1918 when Japanese scientists discovered that painting the ears of rabbits and mice with coal tar extracts produced tumors, some of which were malignant (Yamagiwa and Ichikawa, 1918). 

Dr vonHofmann moved back to Germany in 1874 where he established a large scale coal tar industry... 

Benzene, naphthalene, toluene, and the xylenes are naturally occurring compounds obtained from coal tar. Industrial synthetic methods, called catalytic reforming, utilize alkanes and cycloalkanes isolated from petroleum. Thus, cyclohexane is dehydrogenated (aromatization), and n-hexane(cycli> zation) and methylcyclopentane(isomerization) are converted to benzene. Aromatization is the reverse of catalytic hydrogenation and, in the laboratory, the same catalysts—Pt, Pd, and Ni—can be used. The stability of the aromatic ring favors dehydrogenation. 

E.Rhodes, USBurMinesInfoCirc 7409 (1947) (German high-temperature coal tar industry)... 

Solvent extraction has found application for many years in the coal tar industry. Extraction of phenols from coal-tar distillates by washing with caustic soda solution can be considered such a process. In the isomer separation, a process for separation of m- and p-crcsol by dissociation extraction has been reported. Work is in progress in several parts of the world to use solvent extraction for the direct manufacture of chemicals from coal. Crude tall oil is a byproduct of pulp mills. It is refined by solvent extraction using propane or furfural. 

The modem dye industry is built upon the coal tar industry as its source of material, and upon the Kekule benzene theory as its scientific basis. Without these foundations, the dye industry could not have been developed. 

The aliphatic and aromatic hydrocarbons may contain a substituted halogen element and are often referred to as halogenated hydrocarbons. These include, for example, perchloroethylene, trichloroethylene, and carbon tetrachloride. Organic solvents are very useful and have extensive applications in industry because they help in the manufacture of oils, fats, resins, rubber, and plastics. In fact, the role of organic solvents increased in the latter half of the nineteenth century with the development of the coal-tar industry. The wide application of organic solvents grew and became diverse and global. 

Thus speaks Heinrich Caro, one of the prominent workers in the development of the coal tar industry in Germany. 

Coke.—The solid non-volatile residue or coke is used as fuel, especially in the iron and steel industry. Most of the coke so used is made in coke ovens in which the gas and liquid products were originally allowed to escape into the air and were wasted. In recent years much of the coal tar formerly wasted is now recovered. Thus with the development of our knowledge of the benzene series of compounds, which include valuable dyes, explosives, medicines, etc., this substance that was formerly thrown away has become a most important industrial product. So important are the compounds obtained, either directly or indirectly, from it that the name coal tar has become an adjective of common use and significance as shown by the terms, coal tar industry y coal tar productsy coal tar dyes. 

See William Reginald Ormandy, Britain and Germany in relation to the chemical trade, Royal Society of Arts, 2 December 1914, reprinted in Chemical News, 111 (1 January 1915), 3-8 The war and British economic policy The aniline dye industry, Chemical News, 111 (16 Febmary 1915), 97 The war and British chemical industry, Nature, 95 (1 April 1915), 119-20. See also Percy F. Frankland, The chemical industries of Germany, Journal of the Society of Chemical Industry, 24 (7), reprinted in Chemical News, 111 (18 May 1915), 255-257 (4 June), 266-268 (11 June), 277-280, 291. The well-known facts of the coal tar dye industry and its takeover by Germany were assembled for a popular readership in The British Coal Tar Industry Its Origin, Development and Decline, edited by W.M. Gardener (London, 1915). 

As an aside, the nomenclature of the coal tar industry, like that of the petroleum industry (Speight, 2007), needs refinement and clarification. Almost any black, undefined, semisolid-to-liquid material is popularly, and often incorrectly, described as tar or pitch whether it be a manufactured product or a naturally occurring substance (Chapter 16). However, to be correct and to avoid any ambiguity, use of these terms should be applied with caution. The term tar is usually applied to the volatile and nonvolatile soluble products that are produced during the carbonization or destructive distillation (thermal decomposition with the simultaneous removal of distillate) of various organic materials. By way of further definition, distillation of the tar yields an oil (volatile organic products often referred to as benzole) and a nonvolatile pitch. In addition, the origin of the... 

Until 1950 the coal-tar industries were the major source of aromatics in both Europe and the U.S. Thereafter, they contracted slowly, while demand for aromatics increased. The chemical industry again turned to petroleum, which eventually supplied some 90% of benzene (4-5 Mt) and other aromatic hydrocarbons worldwide. 

This unit differs from the other contactors described previously in that it is a horizontal design. It is also unique in that the rotating buckets disperse both liquid phases in turn. It is particularly useful for systems where the settling time is relatively large because it generates a large droplet size distribution and has been used in the coal-tar industry. Units with diameters of 1.8 m (6 ft) have been constructed which have a reported throu iput of about 8600 L/h-rtr (210 gai/h-ft ). 

A pitch, as supplied by a manufacturer, is normally characterized by the softening point and the penetration value, hardly sufficient to describe the composition. The petroleum and coal tar industries, unfortunately, have somewhat different methods of further... 

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