Лако-красочные материалы — производство

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 last thirty years have seen a very large increase in the number of raw materials for the dye industry, obtained by the dry distillation of coal tar. To the hydrocarbons known for a long time, such as benzene, toluene, xylene, naphthalene, and anthracene, have now been added many new compounds which previously were known only in scientific circles. These compounds could not be considered for industrial appli­cation until they had been obtained in large quantity and at low cost by coal tar distillation. Some of these newer raw materials are, for ex­ample, carbazole, quinoline, pyridine, acenaphthene, pyrene, chrysene, indene, and other coal tar constituents which are now used in large quan­tities for the preparation of valuable dyes. Various other hydrocarbons and nitrogen-containing compounds have beep placed on the market but have found no industrial application as yet, although some of these may prove to be useful in the future. No uses have been found for phenan — threne, for example, although it is available in almost unlimited amounts. The homologs of benzene which are present in coal tar in only relatively small quantities have also been synthesized, in recent years, from ali­phatic hydrocarbons.

With the increasing demands of the dye plants, the purity hf the raw materials has steadily improved, and today many of these products may be called chemically pure. Modem methods have permitted the direct manufacture of pure compounds by fractional distillation *and fractional crystallization. These improved techniques of the tar industry have resulted from extensive work and they constitute one of the foun­dations for the manufacture of intermediates for the dye industry.

Generally, the supply of the necessary raw materials satisfies the demand. It is interesting to note, however, that in recent years there has been an increase in the price of naphthalene, which previously was usually available in excess. This situation has arisen because changes in gas manufacture by chamber distillation have resulted in the pyrolytic decomposition (“cracking”) of the greater part of the naphthalene present in the tar. This situation has naturally had an effect on dye inter­mediates derived from naphthalene (phthalic anhydride, anthraqui — none, H acid, naphthols, etc.).