Aromatic hydrocarbons in reformed gasoline can be separated by extraction. Aromatic hydrocarbons in pyrolysis gasoline are often separated by extraction, but unstable diolefins, monoolefins and sulfur-containing compounds need to be removed by catalytic hydrogenation before extraction (see aromatic hydrocarbon extraction). Because of the high content of aromatics in pyrolysis gasoline, aromatics can also be separated by extractive distillation. Commonly used extractants are N, N- dimethylformamide, N- formylmorpholine, ν-methylpyrrolidone, sulfolane and so on. In the extractive distillation column, non-aromatic hydrocarbons are distilled from the top of the column, and aromatic hydrocarbons and solvents are left at the bottom of the column. Compared with the extraction method, this method has the advantages of simple equipment and low operating cost, but the yield of aromatic hydrocarbons is slightly lower. Coke oven gas, a by-product of coking, is absorbed to obtain an absorption solution, from which crude benzene fractions containing C8 and C9 aromatic hydrocarbons can be separated by rectification. Coal tar is a by-product of coal coking, which can be fractionated to obtain light oil, phenol oil, naphthalene oil, washing oil, anthracene oil, asphalt and other fractions, and then separated by rectification, crystallization and other methods to obtain benzene series, naphthalene series and anthracene series aromatics. Among aromatic hydrocarbons, benzene and p-xylene are widely used and in great demand; Toluene, m-xylene, C9 aromatics and other uses are less. In industry, toluene, m-xylene and C9 aromatics can be converted into benzene and p-xylene by various conversion processes. Alkylation, dealkylation, isomerization, disproportionation and transalkylation are mainly carried out in the conversion process.