Pseudocumene Naphthalene

FIGURE 5.2 Some primary raw materials used for dye production.

tar is the traditional source of dye intermediates, and it is a complex mixture of substances obtained from bituminous coal by distillation. After distillation, five fractions with a range of boiling points (b.p.) are produced: light oil (230 to 270°C b.p.), middle oil (170 to 230°C b.p.), heavy oil (230 to 270°C b.p.), anthracene oil (b.p. > 270°C), and pitch (nonvolatile residue). Light oil is redistilled and fractions are treated with caustic soda (sodium hydroxide) solution and concentrated sulfuric acid. Fractional distillation is carried out and raw materials (benzene, toluene, and xylenes) are obtained. In contrast, naphthalene is obtained from the middle oil by cool precipitation. Crystals are pressed and treated with caustic soda, sulfuric acid, and finally distilled or sublimed.10

At present, coal tar is an important source of these raw materials but petrochemicals have acquired increased importance. In particular, petroleum is the principal source of raw materials for the production of certified colorants in the United States.22 In the production of certified colorants, large quantities of other substances are used: inorganic acids and salts, aliphatic and alicyclic compounds (alcohols, ketones, acids, chlorides, and sulfates), as well as heterocyclic compounds (pyridine and

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