Study on Solvent Extraction Separation of Polymethyl-Substituted Monocyclic Aromatics from FCC LCO and Its Interaction Mechanism

The efficient separation of aromatics from fluid catalytic cracking light cycle oil is crucial for improving oil quality and realizing the high-value utilization of aromatics. In this study, a two-step extraction-stripping high-efficiency separation method was developed, which successfully achieved the separation of nearly 99.99% pure aromatics. Focusing on the separation characteristics of polymethyl monocyclic aromatics, the extraction performances of sulfolane, dimethyl sulfoxide, and N, N-dimethylformamide was analyzed by GC-MS. Under the conditions of 318.15 K and 101.325 kPa, the liquid-liquid equilibrium (LLE) data of the extractant-p-xylene-heptane ternary system were determined. The results of the separation factor and distribution coefficient showed that sulfoxide had the best selectivity for polymethyl monocyclic aromatics, making it a potential high-efficiency extraction solvent. Furthermore, combined with density functional theory, the mechanism of solvent extraction of p-xylene from heptane was explored at the molecular level. Analyses of electrostatic potential, interaction energy, and reduced density gradient revealed that the main interaction was the van der Waals force. The LLE data were accurately correlated using the NRTL and UNIQUAC thermodynamic models, with the root-mean-square deviation values all below 0.0098. This study not only provides an efficient process for separating but also clarifies the structure-activity relationship between solvent molecular structure and extraction performance from both experimental and theoretical perspectives, providing a theoretical basis for the design and selection of high-performance separation solvents.