Phenol production: basic methods

Phenol is a colorless substance of a crystalline structure with a very specific odor. This substance is widely used in the production of various dyes, plastics, various synthetic fibers (mainly caprone). Before the development of the petrochemical industry, phenol was produced 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 the objects around us.

Phenol, the receipt of which became an urgent necessity in connection with the appearance 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 it, in turn, is an important component of phenoplasts. Also, a large amount of phenol is processed into cyclohexanol, which is necessary for manufacturing synthetic fibers on an industrial scale.

Another important field of application of phenol is the production of a mixture of creosols, which is synthesized in a creosol-formaldehyde resin used to make a variety of medical preparations, antiseptics and antioxidants. Therefore, today the production of phenol in large quantities is an important task of petrochemistry. A lot of methods have already been developed that make it possible to produce this substance in sufficient quantities. Let's dwell on the main ones.

The oldest and most proven method is the alkali melting process, which is characterized by a high consumption of sulfuric acid for the sulfonation of benzene and caustic followed by their fusion into the benzenesulfonate salt from which the substance is directly released. The production of phenol by chlorination of benzene followed by saponification of chlorobenzene with caustic soda is cost-effective only if there is a large amount of cheap electricity necessary for the production of caustic and chlorine. The main drawbacks of this technique are the need to create high pressure (at least three hundred atmospheres) and an extremely significant degree of equipment corrosion.

A more modern method is the preparation of phenol by decomposition of isopropylbenzene hydroperoxide. True, the scheme for isolating the required substance here is rather complicated, since it involves the preliminary production of hydroperoxide by the benzene alkylation process with the propylene solution. Further, the technology provides for the oxidation of the resulting isopropylbenzene with an air mixture to form a hydroperoxide. As a positive factor of this technique, one can note the production in parallel with phenol of one more important substance, acetone.

There is also a procedure 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 fast oxidation, which leads to accelerated aging of the oil and the formation of viscous resin-like fractions in it.

But the most modern method and the latest achievement of the petrochemical industry is the production of 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 oxidizing ammonia with air or by separating it from adipic acid. More precisely, from its by-products formed in the process of synthesis. This technology is able to provide a high-purity phenol with a minimum total content of impurities.