Study On The Modification Of Y Zeolite For Hydrocracking Catalysts

As one of the most important technologies for oil refinery in modern society,hydrocracking technology plays a crucial role in heavy oil conversion and oil products upgrading,especially as a feasible way to produce middle distillate from VGO.The key to realizing hydrocracking process is the catalyst which is composed of acid support,active components and additives.Y zeolite with the superior stability and moderate acidity,is widely used as the support for hydrocracking catalyst.However,the feeds for hydrocracking are becoming heavier and conventional Y zeolite that treats light feeds is unprofitable.Its intrinsic micropores remain a limitation for the application in transformation processes involving bulky molecules,so the introduction and connectivity of mesopores is a key factor for the high efficiency catalyst design.Besides,the optimization of acid distribution is an important aspect.In this study,industrial NaY zeolite was modified by the combination of hydrothermal treatment and acid leaching to introduce mesopores and improve Si/Al ratio.With the assistance of characterization techniques,the influences of ion exchange,hydrothermal treatment and oxalic acid treatment on pore structure and acid properties were investigated systematically.The results showed that the content of Na⁺could be greatly decreased to about 0.5%by controlling the times of ammonium ion exchange;relative crystallinity decreased with the decrease of Na⁺content after hydrothermal treatment,so the number of exchange times should be 2 in order to keep the framework complete;hydrothermal treatment could introduce secondary pores and improve Si/Al ratio from around 4 to 9,and the optimized condition was600?,3h.By combining the hydrothermal treatment and oxalic acid leaching,the results indicated that the non-framework aluminum that was mainly produced from hydrothermal treatment could be removed by acid treatment,which was useful to increase mesopore surface area?to 128m²/g?and mesopore volume(to 0.17cm³·g^-1).The Si/Al ratio was improved up to about 16 because of the removal of framework aluminum.Besides,more middle strong acid sites were introduced after acid leaching,which was essential for the cracking reaction under high temperature.The TEM images showed clearly more channel-like mesopore after acid leaching compared with the industrial USY,which was consistent with the N₂ sorption results.As the acid component of hydrocracking catalyst,the total yield of gasoline and diesel were improved by approximately 4%compared with the commercial USY.Therefore,it proved that the method that involves hydrothermal treatment and oxalic acid leaching has promosing prospects for industrial application.