Benzene is an organic compound, the simplest aromatic hydrocarbon, with the chemical formula C6H6. It is a colorless transparent liquid with carcinogenic toxicity and has a strong aromatic odor. It is slightly soluble in water, easily soluble in organic solvents [27], and can also be used as an organic solvent. The ring system of benzene is called the benzene ring, and the structure of the benzene ring after removing one hydrogen atom is called benzene, represented by Ph. Therefore, the chemical formula of benzene can also be written as PhH. Benzene is a basic raw material in the petrochemical industry, and its output and production technology level are some of the indicators of a country's petrochemical development level.
On October 27, 2017, the International Agency for Cancer Research of the World Health Organization released a preliminary list of carcinogens for reference, with benzene listed as a Class 1 carcinogen.
Benzene can be obtained by incomplete combustion of substances with high carbon content. In nature, both volcanic eruptions and forest fires can generate benzene. Benzene is also present in cigarette smoke. The main component of coal tar obtained from coal carbonization is benzene.
Until World War II, benzene was still a byproduct of the coking process in the steel industry. This method can only extract 1 kilogram of benzene from 1 ton of coal. After the 1950s, with the increasing demand for benzene in industry, especially in the increasingly developing plastic industry, the process of producing benzene from petroleum emerged. Since the 21st century, most of the global benzene has come from the petrochemical industry. The three most important processes for industrial production of benzene are catalytic reforming, toluene hydrogenation dealkylation, and steam cracking.
Extracting from coal tar
The light tar generated during the coal coking process contains a large amount of benzene. This is the initial method of producing benzene. The generated coal tar and gas are combined through washing and absorption equipment, and high-boiling coal tar is used as a washing and absorption agent to recover the coal tar from the gas. After distillation, crude benzene and other high boiling fractions are obtained. Crude benzene can be refined to obtain industrial-grade benzene. The purity of benzene obtained by this method is relatively low, environmental pollution is severe, and the process is relatively backward. [13]
Extracting from petroleum
Extracting benzene from petroleum products is the most widely used preparation method, as it contains a small amount of benzene in crude oil.