Benzene can be obtained by incomplete combustion of substances with high carbon content. In nature, both volcanic eruptions and forest fires produce benzene. Benzene also exists in cigarette smoke. Until World War II, benzene was a by-product in the coking process of iron and steel industry. This method can only extract 1 kg benzene from 1 ton coal. After 1950s, with the development of industry, especially the plastic industry, the process of producing benzene from petroleum came into being. Now most of the benzene in the world comes from petrochemical industry. The three most important methods to produce benzene in industry are catalytic reforming, hydrodealkylation of toluene and steam cracking. The light tar produced by coal during coking is extracted from coal tar, which contains a lot of benzene. This is the original method of producing benzene. The generated coal tar and gas pass through washing and absorption equipment. High boiling point coal tar is used as washing and absorbent to recover coal tar from coal gas, and crude benzene and other high boiling point fractions are obtained after distillation. Crude benzene can be refined to obtain industrial grade benzene. The benzene obtained by this method has low purity, serious environmental pollution and backward technology. Crude oil extracted from petroleum contains a small amount of benzene. Extracting benzene from petroleum products is the most widely used preparation method. [Editor] Catalytic reforming here refers to the process of cyclodehydrogenation of aliphatic hydrocarbons to aromatic hydrocarbons. This is a process developed during the Second World War. At 500-525℃ and 8-50 atmospheric pressure, various aliphatic hydrocarbons with boiling point between 60-200℃ are catalyzed by platinum-rhenium catalyst. It is converted into aromatic hydrocarbons such as benzene by dehydrocyclization. After extracting aromatic products from the mixture, benzene can be separated by distillation. These fractions can also be used as high octane gasoline. [Editor] Steam cracking Steam cracking is a process of producing olefins from low molecular alkanes such as ethane, propane or butane and petroleum components such as naphtha and heavy diesel oil. One of its by-products is cracked gasoline rich in benzene. Benzene and other components can be fractionated. Cracked gasoline can also be mixed with other hydrocarbons as gasoline additives. The content of benzene in pyrolysis gasoline is about 40-60%, and it also contains other unsaturated components such as diene and styrene. These impurities are easy to react further during storage to generate macromolecular colloid. Therefore, these impurities and sulfides in cracked gasoline should be removed by hydrotreating first. And then proper separation is carried out to obtain benzene products. Editor: The components of benzene-containing fractions obtained by different methods of aromatic hydrocarbon separation are very complicated, and it is difficult to get results by ordinary separation methods. Usually, liquid-liquid extraction or extractive distillation is used to separate aromatic hydrocarbons. Then, benzene, toluene and xylene were separated by conventional separation methods. According to different solvents and processes, there are many separation methods. Udex method: jointly developed by National Highway Chemical Company and UOP Company in 1950. At first, diethylene glycol ether was used as solvent, and later it was improved to triethylene glycol ether and tetraethylene glycol ether as solvent. The process adopts multi-tube extractor. The yield of benzene is 100%. Suifolane method: developed by Dutch Shell Company and patented by UOP Company. The solvent is sulfolane, and the extraction is carried out by rotating extraction tower. This product needs to be treated with white clay. The yield of benzene is 99.9%. Arosolvan method: developed by Lurgi Company of the Federal Republic of Germany in 1962. The solvent is N- methylpyrrolidone (NMP). In order to improve the yield, 10-20% glycol ether is sometimes added. A specially designed mechanical extractor is adopted. The yield of benzene is 99.9%. IFP method: developed by French Institute of Petroleum Chemistry on 1967. Anhydrous dimethyl sulfoxide as solvent and butane as stripping. The yield of benzene is 99.9%. Formex method: developed by Italian SNAM Company and LRSR Petroleum Processing Department in 197 1