Selective extraction of aromatics from FCC diesel using organic solvents: Separation performance and mechanism of dicyclic and tricyclic compounds

Planarity and solvent‑group electronegativity jointly control DAHs/TAHs selectivity. • DMSO extracts DAHs via spatial compatibility; SUL enriches TAHs by tight stacking. • VDW forces and weak H‑bonds serve as molecular descriptors for arene selectivity. • Competitive extraction and solvation, not binary interactions, govern real separation. The selective separation of dicyclic aromatics (DAHs) and tricyclic aromatics (TAHs) from fluid catalytic cracking (FCC) diesel is critical for upgrading diesel quality and achieving high-value utilization of aromatic components. In this study, sulfolane (SUL), dimethyl sulfoxide (DMSO), and N, N-dimethylformamide (DMF) were adopted as extractants. The extraction performance was first evaluated using real FCC diesel feedstock, and a ternary model system was further established to reveal the intermolecular selectivity mechanism. Liquid-liquid equilibrium (LLE) measurements for the solvent/1-methylnaphthalene/phenanthrene-n-tetradecane ternary systems were performed at 318.15  K and 101.325  kPa. Distribution coefficients and separation factors were calculated to quantify extraction selectivity. The NRTL and UNIQUAC models were employed to correlate the experimental LLE data; the root-mean-square deviations for the regressed binary interaction parameters were all below 0.01, demonstrating satisfactory fitting precision. Combined with quantum chemical calculations including reduced density gradient and electrostatic potential analyses, the solvent-aromatic intermolecular interaction mechanism was illustrated at the molecular scale. Experimental results from real oil samples indicate that DMSO presents superior extraction capacity for DAHs, whereas SUL exhibits better selectivity toward TAHs. The qualitative selectivity trend derived from the LLE model systems agrees well with the separation behavior observed in practical FCC diesel. Quantum chemical results demonstrate that the planarity of aromatic molecules and the electronegativity of functional groups on solvent molecules dominate separation selectivity, and solvent–solute interactions are mainly governed by van der Waals forces and weak hydrogen bonds. This work identifies the inherent limitations of simplified model systems and provides fundamental equilibrium data and molecular-level mechanistic insights for the future development of industrial aromatic separation processes from FCC diesel. Download: Download high-res image (198KB) Download: Download full-size image