Phenol is a colorless crystalline substance with a very specific odor. This substance is widely used in the manufacture of various dyes, plastics, a variety of synthetic fibers (mainly nylon). Before the development of the petrochemical industry, phenol was obtained exclusively from coal tar. Of course, this method was not able to cover all the needs of the booming industry in phenol, which has now become an important component of almost all of the objects around us.
Phenol, the preparation of which became an urgent necessity in connection with the emergence of an extremely wide range of new materials and substances, of which it is an integral ingredient, is used in the synthesis of phenol-formaldehyde resin. And she, in turn, is an important component of phenoplasts. A large amount of phenol is also processed into cyclohexanol, which is necessary for the manufacture of synthetic fibers on an industrial scale.
Another important application of phenol is the production of a mixture of creosols, which are synthesized into creosolformadelgide resin, which is used to make many medications, antiseptics, and antioxidants. Therefore, today the production of phenol in large quantities is an important task in petrochemistry. Many methods have already been developed to produce this substance in sufficient quantities. Let us dwell on the main ones.
The oldest and most proven method is the alkaline melting method, which is characterized by a high consumption of sulfuric acid for sulfonation of benzene and caustic, followed by their fusion into a benzenesulfonate salt, from which this substance is directly isolated. Obtaining phenol by chlorinating benzene followed by saponification of chlorobenzene with sodium hydroxide is cost-effective only if there is a large amount of cheap electricity needed for the production of caustic and chlorine. The main disadvantages of this technique are the need to create high pressure (at least three hundred atmospheres) and an extremely significant degree of corrosion of the equipment.
A more modern method is to obtain phenol by decomposition of isopropylbenzene hydroperoxide. True, the scheme for isolating the required substance is rather complicated here, since it involves the preliminary production of hydroperoxide by the alkylation of benzene with a solution of propylene. Further, the technology provides for the oxidation of the resulting isopropylbenzene with an air mixture to form hydroperoxide. As a positive factor of this technique, it is possible to note the receipt in parallel with phenol of another important substance - acetone.
There is also a method for the isolation of phenol from coke and semi-coke resins of solid fuel materials. This procedure is necessary not only to obtain valuable phenol, but also to improve the quality of various hydrocarbon products. One of the properties of phenol is its rapid oxidation, which leads to accelerated aging of the oil and to the formation of viscous resinous fractions in it.
But the most modern method and the latest achievement in the petrochemical industry is to obtain phenol from benzene directly by oxidizing it with nitrous oxide. The whole process is carried out in a special adiabatic reactor in which a zeolite-containing catalyst is located. The starting nitrous oxide is obtained by oxidation of ammonia with air or by isolation from adipic acid. More precisely, from its by-products formed in the synthesis process. This technology is able to provide high-purity phenol with a minimum total impurity content.