Study On The Modified Y Zeolites Of Hydrocracking Catalysts

Hydrocracking is a process that the raw material catalytic conversion occurred in the presence of hydrogen and a catalyst under pressure and heat. Series of reactions such as hydrogenation, desulfurization, denitrification, molecular skeleton structure rearrange and cracking will be completed in the hydrocracking process. The development of hydrocracking technologies is a ripe experience, while the hydrocracking catalysts still need updating and upgrading. NaY zeolite was modified by ammonium ion exchange, hydrothermal treatment, oxalic acid treatment in this paper. The temperature and time has little effect on the removal of sodium oxide content, while the concentration of influences its sodium oxide greatly. The hydrothermal treating temperature should be controlled to 550℃to maintain higher crystallinity. Oxalic acid treatment can not only dealumination, and can reduce sodium oxide content.In the present researches, Y zeolites were modified by different isomorphous substitution methods, including ammonium ion exchange, hydrothermal treatment and oxalic acid treatment. The effects of these modification on Si/Al molar ratio, relative crystallinity, unit cell parameter, specific surface area, pore structure and framework vibration of Y zeolites were investigated by using XRF, XRD, N2 adsorption-desorption isotherms and FT-IR. The acidity of modified Y zeolites was also measured by NH3-TPD and Py-IR. The results showed that with the increase of modification degree, the Si/Al molar ratio of Y zeolite framework increased from 4.99 to 12.35, and the unit cell parameter (ao) decreased from 2.4630 nm to 2.4462 nm. A large quantity of non-framework aluminum was found in Y zeolites modified by hydrothermal treatment, and could be effectively removed by oxalic acid treatment. After oxalic acid treatment, Y zeolites showed higher specific surface area and secondary pore volume. The total acidity decreased and the mediate strong acid increased. The strong Lewis acidity could be enhanced by hydrothermal treatment, and the oxalic acid treatment could increase the ratio of Bronsted acid to Lewis acid. These modified Y zeolites as the component of acidic matrix, the Ni-W hydrocracking catalysts were prepared by incipient wetness impregnation method. The catalysts were tested on the hydrocracking of n-decane to study the effect of acidity on activity and isomerization selectivity. Cyclohexane was also chosen to investigate the effect of zeolites on the monocyclic alkanes hydroconversion in activity and selectivity of ring opening. Finally, we select one method of Y modification for the preparation of hydrocracking catalyst.