Characteristics of zeolite-modified NiMo/Al2O3 catalysts and their hydrotreating performance for light cycled oil

摘要

The performance of a widely used commercial catalyst, NiMo/Al2O3, might be not adequate to meet more stringent regulations for the fuel products; therefore, a lot of research has been devoted to improving its performance. In this study, three different modified zeolites were added in NiMo/Al2O3 catalyst to investigate the selective improvement of the hydrodesulphurization (HDS) and hydrodenitrification (HDN) activity. The catalysts were characterized by N-2 adsorption, pyridine-infrared spectroscopy (IR), H-2-temperature program reduction (H-2-TPR), x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), and their catalytic activity was tested in the HDS and HDN of light cycle oil (LCO). Characterization results revealed that the catalyst surface area increased but the pore volume and average pore size decreased by adding modified zeolite. The activity evaluation result showed that the NiMo/MB catalyst had the highest activity and meanwhile decreased the final boiling point from 520.8 to 457 degrees C. The sulphur decreased by 97.65% from 13000 to 305ppm and the nitrogen reduced by 99.74% from 496 to 1.29ppm in LCO hydrotreating, notably for NiMo/MB catalyst. The acid properties indicated that zeolite brought some strong and ultra-strong acidic sites, which might favour a cracking reaction and reduce the liquid recovery yield. However, only 1.99 and 1.34wt% of the LCO were cracked over the zeolite beta and zeolite modified beta respectively, indicating a slight cracking process. These results suggest that an added modified beta not only raised the quality of LCO distillation but also avoided the overcracking of hydrocarbons.