By Eric Bank, MBA, MS Finance
Updated Mar 24, 2022
Benzene (C6H6) is the simplest aromatic hydrocarbon. Its planar ring of six carbon atoms shares delocalized electrons, giving it a bond order between single and double bonds. At room temperature it is a colorless liquid with a sweet, gasoline‑like odor, boiling at 176.2 °F (80 °C) and freezing below 41.9 °F (5 °C). While essential in industrial chemistry, benzene is highly flammable and a known human carcinogen, requiring careful handling and regulation.
Cracking is the primary industrial route for producing benzene from crude oil. The process begins by vaporizing crude petroleum, adding steam, and then exposing the mixture to a furnace at 1,300–1,650 °F (700–900 °C). This generates a complex stream of hydrocarbons—known as raw pyrolysis gas—which contains aromatic species such as benzene and toluene. Solvents, typically alcohols, extract these aromatics, which are subsequently separated by fractional distillation to isolate pure benzene.
Naphtha, a straight‑chain hydrocarbon mixture derived from petroleum or natural gas, can be converted into benzene through catalytic reforming. After removing sulfur impurities, the feed is mixed with hydrogen and heated to 930 °F (500 °C) under 5 atm pressure. A platinum or rhenium catalyst promotes the conversion of aliphatic chains (e.g., hexane) into aromatic rings. The resulting product stream is then distilled to recover benzene, toluene, and other aromatics.
During naphtha reforming, toluene (methylbenzene) is produced as a by‑product. Disproportionation offers a way to upgrade this stream into higher‑value aromatics. A mixture of toluene and hydrogen is passed over a zeolite catalyst at 800–900 °F (425–480 °C) and 15–25 atm pressure. The reaction yields benzene and xylene, which are separated by distillation. Unconverted toluene is recycled back into the reactor.
Hydrodealkylation is another method to synthesize benzene from toluene. In this process, toluene and hydrogen are compressed to 20–60 atm and heated to 930–1,220 °F (500–650 °C). Catalysts such as chromium, molybdenum, or platinum facilitate the cleavage of the methyl group, producing benzene and methane. The benzene is recovered by distillation, and the hydrogen is recycled. This route can achieve a conversion efficiency of up to 90 %.
