Selective Extraction of Aromatics from Slurry Oil with Subcritical Water

The selective separation of aromatics from slurry oil (SLO)-a low-value byproduct of fluid catalytic cracking-remains a major industrial challenge. This study investigates the use of subcritical water (Sub-CW) as a green and tunable solvent to extract aromatics from SLO in a semi-batch system operating at 250-325 °C. At 325 °C and a water-to-oil mass ratio of 6:1, the extract yield reaches 16 wt%, with aromatic hydrocarbons accounting for over 90 wt% of the extract, predominantly composed of 3- to 4-ring polycyclic aromatic hydrocarbons. Comprehensive characterization via simulated distillation, SARA analysis, FT-IR, and ¹H-NMR confirms the selective enrichment of aromatics and effective separation from saturates and asphaltenes. To elucidate the molecular basis of this selectivity, principal component analysis of Hansen solubility parameters was performed. The results revealed a temperature-dependent solubility trend in Sub-CW, whereby the affinity for hydrocarbons follows the order aromatics > cycloalkanes > alkanes. This solubility preference, supported by both experimental data and theoretical analysis, offers new insight into subcritical solvent design and provides a basis for process intensification in SLO valorization.