The role of hierarchical Y zeolites on the catalyst performance of diesel Hydrodesulfurization Process

Hydrodesulfurization is one of the effective methods to remove sulfur compounds from oil fractions and improve fuel quality. One of the major challenges in this process is to find the proper catalyst support that performs best. In the meantime, modified supports with zeolite have allocated a lot of attention due to their strong acidic sites, specific surface area and high hydrothermal and chemical stability; But the acidity and volume of zeolite mesopores need to be corrected.

In this study, first, hierarchical Y zeolite was prepared using post-synthesis (Dealumination) and using ammonium form of zeolite and NH4F solution (0.75 M) at 90˚C for 3h under reflux conditions. Physicochemical properties of zeolite were investigated by BET, FESEM, FTIR, AAS and XRD analyzes. Modified zeolites were used in the support synthesis of the HDS process catalyst. The sulfidation and performance evaluation of the prepared catalysts were carried out in the fixed-bed microreactor were performed with diesel cutting feed from the Isomax unit of the target refinery.

The results show that the volume of mesopores, specific surface area and SiO2/Al2O3 ratio in hierarchical zeolites has increased 0.073 cm3 g-1, 783.36 m2 g-1 and 5.2, respectively (initial values are 0.032 cm3 g-1, 567.18 m2 g-1 and 4.5). The results of zeolite analysis show the preservation of the structure and crystallinity during the zeolite modification process. The effect of zeolite modification, especially the Si/Al ratio variations, mesopores and specific surface area, was investigated on the activity of NiMo/Zeolite+Al2O3 catalysts. Increasing the acidity and improving the physicochemical properties of the modified zeolites has increased the catalyst performance in the process of diesel hydrodesulfurization (Conversion= 90%). Improving the activity of catalysts can be attributed to the positive effect of zeolites on the dispersion of the metallic site, surface area, acidity, optimal size of pores and volume of catalyst mesopores.