Coal Tar Production Essays

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The complete process of coal tar production is shown in Figure 1. The coal tar is produced by carbonization of coal. In this process, the coal is heated at 900-1100 ºC and the evolved vapors are condensed to form liquid, from which ammonia is removed to obtain a black viscous crude coal tar. The composition of tar so obtained depends upon the origin and composition of starting material used viz. bituminous (soft) coal, anthracite (hard) (Arnold 1997, Thami 2002).
Crude coal tar can be further purified using various techniques viz. solvent extraction, fractional distillation or coloum chromatography. The extraction of crude coal tar with alcohol containing 5% w/w Tween 80 produces Liquor carbonis detergens (LCD). Similarly, the
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It is most commonly analyzed with either Liquid Chromatography having Ultraviolet/ Fluorescence detection (HPLC/UV, HPLC/FD) or Gas Chromatography coupled with Mass Spectroscopy (GS-MS) (EPA 1994; Litofsky1999; Gruber et. al., 1970). Both the techniques offer high sensitivity and selectivity. However, the high cost of equipment and long run time, especially for LC, are the barriers for their utilization in routine analysis. The other techniques which can be been explored to characterize the coal tar are Spectrofluorimetry (Li 1994, Raza 2012,), Nuclear magnetic resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR) (Nelson 1996, Cerny 1991).
Pharmacological action
Despite its long history of use and wide acceptance, the exact mechanism of action of coal tar is still elusive. Coal tar is known to posses keratolytic, anti-pruitic, anti-mitotic, and anti inflamatory activities (Paghdal, 2009);; Roelofzen 2007). The researchers have put forward many theories to explain these pharmacological actions viz. suppression of DNA synthesis, inhibition of sebum production, photosensitizing effects within the range of the ultraviolet light A (UVA) and visible light spectrum (Gruper 1971, Arnold, 1997, Thami, 2002, Everett 1961, Kaidbey 1977). The constituents that are thought to be responsible for these therapeutic dermatologic effects include the followings;
(1) Acridine compounds in the
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