Extraction and Separation of Polycyclic Aromatic Hydrocarbons from Catalytic Cracking Diesel

The content of polycyclic aromatic hydrocarbons (PAHs) in catalytic cracking diesel is up to 40–70 wt %. It is economical and highly desirable to extract PAHs from catalytic cracking diesel, which helps to solve the problem of diesel oversupply and aromatic insufficiency in China. In this study, liquid–liquid extraction of PAHs with tetramethylene sulfone (i.e., sulfolane) as the extractant is carried out under atmospheric pressure and low temperature. First, the effect of an extractant on the selectivity and distribution coefficient of aromatic hydrocarbons is investigated, and sulfolane is chosen as the extractant. The correlation between the extraction performance of the extractant and its physical parameters is studied. The results show that the greater the difference of the polar force parameters between the aromatics and the extractant, the higher is the selectivity of the extractant for aromatics. The dipole moment difference between the extractant and aromatic mixture is less than that between the extractant and raffinate, so the solubility of the extractant compared to that of the aromatic mixture is better. Under the optimal extraction conditions (sulfolane/catalytic diesel volume ratio, 1.4; extraction temperature, 46 °C; extraction time, 5 min; and phase separation time, 5.5 min) and aromatic recovery conditions (water/(sulfolane + aromatic hydrocarbon) volume ratio, 0.8; extraction temperature, 50 °C; extraction time, 4 min; and phase separation time, 5 min), the quality yield of aromatic products is 29.87 wt %, and the purity of aromatics is 99.07 wt %. The diesel oil before and after extraction is analyzed by GC–MS. Further, the cetane number increased from 33.13 to 49.06. The regenerated extractant is used to extract aromatic hydrocarbons, and it is recycled five times. The yield of aromatics at each time is >28 wt %, and the aromatic purity is >97 wt %.