Hydrocracking of Di-and Triaromatic Hydrocarbons to Monoaromatics over Mixed Bi-functional Catalysts

Abstract

In this study, we present selective hydrocracking of poly (di and tri) aromatic compounds to monoaromatics, such as benzene, toluene, and xylenes (BTX), over a mixture of Pt/Al2O3 and Y zeolites. The polyaromatic compounds feed is a combined simulated model feed, which is similar to light cycle oil (LCO) in composition. The feed is processed in a fixed bed reactor over a catalyst mixture: in the first step, selective hydrogenation of di and tri-aromatic compounds occurs in the presence of Pt/Al2O3 catalyst, followed by conversion of selective hydrocracking of partial hydrogenated polyaromatic hydrocarbons into BTX-rich stream over Y zeolite. The structural properties and Pt dispersion of Pt/Al2O3 were studied by X-ray powder diffraction (XRD) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The acidity of Y zeolite with different SiO2/Al2O3 ratios (SAR) was studied by temperature-programmed desorption of NH3 (NH3-TPD). In addition, the textural properties of catalysts were determined using the N2 adsorption and desorption method. Different parameters such as the effect of temperature, effect of weight hourly space velocity (WHSV), different SAR of Y zeolite, Pt/Al2O3, and Y zeolite wt% ratios, and paraffin concentration were investigated. The maximum BTX yield of ~28 wt.% was obtained at 450°C, WHSV-0.7 h-1, H2 pressure 60 bar, Pt/Al2O3, and Y zeolite ratios of 1:2 (wt%) at Y zeolite SAR of 80. These results suggest that the yield of BTX strongly depends on the hydrogenation function (Pt/Al2O3) and acidity function of Y zeolite. Furthermore, the concentration of paraffin plays a key role in the conversion of diaromatics and triaromatics and desired products of BTX formation.