The core method for industrial aromatic hydrocarbon extraction is aromatic hydrocarbon extraction (AHE). In addition, purification is achieved by combining it with techniques such as distillation and adsorption separation. Specific extraction methods are as follows:
Core Extraction Method: Aromatic Hydrocarbon Extraction
Because aromatic hydrocarbons and non-aromatic hydrocarbons with the same number of carbon atoms in a mixture have similar boiling points, they easily form azeotropes. Conventional distillation cannot effectively separate them, so industrially, extraction (extraction) is used. The core principle is to achieve separation by utilizing the selective dissolution of aromatic hydrocarbons by the solvent:
Process Classification
Liquid-Liquid Extraction Process: The traditional mainstream method. The raw material enters from the middle of the extraction column, and the solvent enters from the top. After countercurrent contact, the aromatic hydrocarbons are transferred to the solvent, and then the aromatic hydrocarbons are separated by distillation, and the solvent is recovered.
Extractive Distillation (Extractive Distillation) Process: This process couples extraction and distillation, simplifying the operation process and achieving higher separation accuracy. It can directly separate the various components of aromatic hydrocarbons. Sulfolane extraction distillation (SED) is currently the mainstream industrial process.
Common Solvents: In industry, sulfolane is the mainstream solvent. It has strong solubility for aromatics, high selectivity, good stability, and is inexpensive and non-toxic, making it the most widely used. Early solvents used diethylene glycol and tetraethylene glycol, but currently, new green solvents such as ionic liquids and eutectic solvents are under research and development.
Raw Material Pretreatment: If it is cracked gasoline feedstock, it needs to be hydrogenated to remove olefins to ensure the purity of the aromatic products. Straight-run gasoline needs to be distilled to remove light fractions below C5.