Basic principles of aromatics extraction

The solvent-liquid extraction principle is based on the different solubility of a solvent for aromatic and non-aromatic hydrocarbons in the de-pentane oil, thus separating the aromatic hydrocarbons from the non-aromatic hydrocarbons and obtaining a mixture of aromatic hydrocarbons. In the aromatic extraction process, the solvent is mixed with the de-pentane oil and divided into two phases (in the container into two layers): one phase consists of solvent and aromatic hydrocarbons that can be dissolved in the solvent, known as the extraction phase (also known as rich solvent, extraction liquid, extraction layer or extraction liquid); the other phase is non-aromatic hydrocarbons that are not soluble in the solvent, known as the residual phase (also known as the residual liquid, non-aromatic hydrocarbons). After the two liquid layers are separated, the solvent and aromatics are then separated, the solvent is recycled and the mixed aromatics are used as raw material for aromatic distillation.

The main indicators of the aromatics extraction process are aromatics recovery, aromatics purity and process energy consumption.
The formula is:
                          Aromatics recovery = Aromatics in the extracted product / Aromatics in the de-pentane oil * 100%

Three basic conditions must be considered when selecting a solvent:
1) High solubility for aromatics.
2) High selectivity for aromatics.
3) A high density difference between the solvent and the raw oil.
Currently, the main solvents used in industry are diethylene glycol ether, triethylene glycol ether, tetraethylene glycol ether, dipropylene glycol ether, dimethyl sulfoxide, cyclobutane sulfone and N-methylpyrrolidone.