Effect of the chemical composition of six hydrotreated light cycle oils for benzene, toluene, ethylbenzene, and xylene production by a hydrocracking process

Abstract

The effect of the chemical composition of the hydrotreated light cycle oil (HDT LCO) on the benzene, toluene, ethylbenzene, and xylene (BTEX) production by a hydrocracking (HCK) procedure, is presented. Six different types of HDT LCOs were obtained by submitting two types of LCOs to hydrotreating (HDT) with different catalysts and experimental conditions. The products were analyzed as mono-, di- and tri-aromatic compounds using the supercritical fluid chromatography (SFC) method (ASTM D5186). The HDT LCOs were subjected to HCK with a 50/50 in weight mixture of nickel-molybdenum on alumina (NiMo/Al₂O₃) and H-ZSM5 (NiMo/H-ZSM5, 50/50) at 375 °C, 7.5 MPa, 1.2 h⁻¹, and 750 m³/m³ H₂/Oil. The HCK products were analyzed by gas chromatography with a flame ionization detector (GC-FID) and divided into five groups: gas, light hydrocarbons (LHCs), BTEX, middle hydrocarbons (MHCs), and heavy hydrocarbons (HHCs).

The results showed that the BTEX formation ranged from 27.0 to 29.8 wt.% and it did not show a significant dependence on the mono-aromatic (59.9 and 75.6 wt.%), total aromatic (61.1–84.2 wt.%) contents or MHCs conversion (58.3–64.3 wt.%) from the departing HDT LCO feedstock. This result implies that, contrary to previous expectations, the BTEX formation does not directly depend on the amounts of total or mono-aromatic compounds when departing from real feedstocks. A GC-PIONA (paraffin, isoparaffin, olefin, naphthene, aromatic) characterization method (ASTM D6623) for mechanism understanding purpose was also carried out.