There are several methods for industrial and laboratory production of benzene, which differ according to which product is selected as the starting material. Modern chemical production as such increasingly uses various aromatic compounds, such as, for example, coke oven gas obtained during the coking of coal. Coal tar and various fractions formed during the distillation of oil are used quite widely .
Coal coking is the most important technological operation in metallurgy; it is necessary for producing coke. There is no need to describe in detail the whole technology on which benzene production is based; suffice it to say that in this case it is formed at the stage when coal decomposes and the decomposition products are coke and volatile substances, primarily coke oven gas. In its pairs is coal tar. When this gas passes through a system of capacitors, the separation of the substances that make it up occurs. After electro- filtering, coke oven gas already contains vapors of organic compounds, including benzene. This production of benzene provides its raw yield of approximately 10–11 kilograms per ton of dry coal.
Coal tar also makes it possible to obtain benzene. The technology here is much like the method in which benzene is produced from coke oven gas. The fact is that coal tar in itself is a rather complex mixture of various aromatic organic compounds in terms of component composition. Moreover, even today, the composition of this compound has not been fully studied, and more than 500 (!) Components have been established. Processing technologically is a two-stage process of separation of the resin into separate fractions. To do this, each of them is exposed to alkalis to remove acidic parts. As a result, solid fractions are formed - anthracene and naphthalene, as well as lungs, which also include benzene.
In industry, it is common to obtain crude benzene, the so-called crude benzene. To obtain a pure compound, crude benzene must be purified from sulfur compounds. In this process, two stages are distinguished. On the first, the sulfur impurities are actually cleaned, and on the second, the purified mixtures are separated by distillation. One of the products of this separation will be benzene.
The most important source of various aromatic compounds is oil. That is why modern benzene production focuses on this product.
Benzene is also isolated from acetylene. Under normal conditions, this substance is a gas; it is colorless, practically insoluble in water, and lighter than air. Among the chemical properties of this gas is the ability to polymerize, and therefore, industry uses the production of benzene from acetylene. This method seems more promising from the point of view of creating and maintaining the conditions of a chemical reaction. The fact is that acetylene, in itself, is very explosive, because its use in industry is associated with the need to observe the strictest technological discipline and the availability of special equipment, especially heat-resistant. At the same time, before obtaining benzene from acetylene, it is sufficient to achieve a temperature of 400 C and conduct it in the presence of graphite. This method was proposed back in 1866 by the French chemist M. Berthelot, however, the yield of the substance was extremely small. Therefore, in today's technologies, the use of various kinds of catalysts is widely used, accelerating the course of the reaction and contributing to an increase in the yield of pure benzene.
In laboratory conditions, benzene, as a rule, is not obtained, but if nevertheless such a need arises, then the method of fusion of benzoic acid with alkali is used. The result of this reaction will be benzene.