Coal tar

Coal tar ( as a drug Pix lithanthracis ) is a by-product of Koksgewinnung from coal. The viscous black mass that gives off a characteristic odor, is obtained from the resulting in the coke oven gases. Coal tar is composed of several thousand, usually aromatic compounds, including hydrocarbons, phenols and nitrogenous bases.

History

Since the discovery by Johann Rudolph Glauber in 1658, the Kohleentgasung has developed in the Steinkohlenverkokung an important industrial process. Coal tar was originally a waste product in the manufacture of illuminating gas, then found in the 19th century in connection with the synthesis of organic dyes from its ingredients a special interest. Scientists like peace-loving Ferdinand Runge, August Wilhelm Hofmann and William Henry Perkin this laid the foundations for the aniline dye industry, the and aniline with names such as color works of Meister, Lucius and Brüning in Höchst, Farbenfabrik of Fr Bayer & Co. in Elberfeld and Badische Soda Factory in Ludwigshafen was connected.

Production

On heating coal in the absence of air in closed vessels at 650 to 800 ° C, the coal decomposes in the following products:

• 80 % coke
• 5% ammonia
• 5% coal tar
• 10% coke oven gas

Coal tar is a by- product of the destructive distillation of coal. The main product of coke is needed in large quantities for the production of iron by smelting of iron ores. Approx. 50 % of the tar used is recovered as tar pitch, which originally was used mainly in road construction. Today, the pitch is the main product and is mainly used as a binder for anodes in aluminum production use.

Use

Coal tar is used among other things as wood preservatives (eg railway sleepers ) and for roofing felt. He was formerly the starting material for the production of a variety of chemical substances, including tar dyes and Carbolineum. Phenol and phenol derivatives such as cresols and xylenol be won in large part still from coal tar.

Purified extracts of coal tar can be used for the treatment of psoriasis (eg, psoriasis ), chronic eczema and neurodermatitis in, but are in Germany because of their carcinogenic properties as an ingredient in cosmetics prohibited; this prohibition does not apply to formulations with a prescription. Since coal tar can be processed poorly because of its high viscosity, using a DAC to as "Liquor Carboni detergent " designated 20 % solution of coal tar soap in alcohol. Coal tar inhibits the itch ( antipruritic ) and acts because of its ingredients, such as cresols bactericidal, fungicidal and insecticidal.

From the pitch contained in coal tar, a synthetic graphite can be obtained by thermal treatment, which is used as an electrode material for electrochemical production of aluminum, for the extraction of electrical steel in the chlor-alkali electrolysis and carbon fibers.

Distillation

From coal tar next phenols, naphthalene and alkyl naphthalenes, biphenyl, anthracene, phenanthrene, fluorene, pyrene, dibenzofuran, dibenzothiophene, quinoline, indole and carbazole are obtained. The separation is obtained by fractional distillation ( in part by vacuum distillation) with subsequent crystallization and extraction, there are different groups:

• Light oil (benzene )
• Carbolic oil ( phenols)
• Naphthalene ( naphthalene)
• Indolöl ( indole )
• Acenaphthene ( acenaphthene )
• Anthracene ( anthracene )
• Pyrenöl ( pyrene )
• Pitch

Hazards

Coal tar contains various substances, some of which are toxic, carcinogenic or harmful to the environment. For these reasons, the use by the Teerölverordnung was severely restricted.