Synthesis And Catalytic Cracking Performance Of Mesoporous Zeolite Y

Zeolite Y is a crystalline microporous aluminosilicates with small micropores.The micropores structure provides large surfaces,strong acid sites,especially excellent shape selectivity for zeolite Y.Because of these properties,zeolite Y plays an important role in chemical industry.However,with the growing lack of resources,the heavy feedstocks are gradually replacing the lighter feedstocks and many large molecules are involved in the reaction.The limited dimensions of the micropores of zeolite Y strongly hinder the diffusion of large molecules and this drawback seriously accelerate the catalyst deactivation in the reaction.In this investigation,hierarchical zeolite Y is prepared using block copolymers P123(PEO20PPO70PEO20)and F127(PEO106PPO70PEO106)as templates,and a direct synthetic route of micro/mesoporous zeolite Y have been developed with the assistance of hydrothermal method.In this paper,firstly,zeolite Y1 is synthesized by directing agent method.Then hierarchical zeolite Y1 is prepared using pluronic P123 and F127 as templates,which is added in the aqueous solution of the zeolite precursor.In this study,we further explore a method to prepare small crystal zeolite Y2 using zeolite precursor with low ratio of silicate to aluminium.Hierarchical zeolite Y2 is also prepared using pluronic P123 and F127 as templates.On the basis of that,cationic surfactant cetyl trimethylammonium bromide(CTAB)is ued as the second template and hierarchical zeolite Y2 is prepared using usingblock copolymer(F127 or P123)and cationic surfactant CTAB as co-templates.The previous zeolites are processed with ions exchanged and hydrothermal treatment.The resulting products are ultra-stabile zeolite Y and are characterized using physical-chemical method.The results reveal that adding templates affects the formation of micro/mesostructure and modulates the acidity in synthesis process.The catalytic cracking properties of the catalysts synthesized were carried out in a micro-activity test(MAT)unit,and light diesel was used as feedstock.Mesoporous zeolite Y is prepared using block copolymers(pluronic P123)as templates.Compared to zeolite Y without using templates,these samples exhibit large mesoporous volume.As addition amounts of P123 template in the preparation process of Y zeolite increased,the mesoporous volumes of zeolites become high and then low.When P123/SiO2 = 0.003,the mesoporous volume of P-MUSY1 is the largest.The XRD and FTIR results of the P-MZY1(P-MZY2)and P-MUSY1(P-MUSY2)zeolites clearly show a series of characteristic diffraction peaks assigning to the Y zeolite,indicating the P123 have a negligible damaging effect on the framework of zeolite Y.SEM images of zeolites show that block copolymer molecules have slightly effect on the morphology of zeolites P-MZY1(P-MZY2)and P-MUSY2(P-MUSY2).The MA value of P-MCAT1 catalyst even reaches 63.34%,which is higher by 3.67% than that without introducing P123 template,presenting a relatively better activity in catalytic cracking.Simultaneously,a significant increase in the gasoline yields is achieved for the products.Moreover,P-MCAT1-B produces less coke,which is lower by 0.51 wt.% than that of CAT1.The acid amounts of mesoporous catalysts P-MCAT2 is more than CAT2.The catalyst P-MCAT2 exhibits a better catalytic cracking property,and the best micro-activity of 63.00% is presented,which is higher by 4.68% than CAT2.The XRD and FTIR results of the F-MZY1(F-MZY2)and F-MUSY1(F-MUSY2)zeolites clearly show a series of characteristic diffraction peaks assigning to the Y zeolite,indicating the F127 have a negligible damaging effect on the framework of zeolite Y.Textural properties analysis show all mesoporous zeolite Y prepared using F127 exhibit large mesoporous volume.When F127/SiO2 = 0.0005,the mesoporous volume of F-MUSY1 exhibits a mesopore volume of 0.200 cm3·g-1,which is larger than the mesopore volume of USY1.Compared to USY1,F-MUSY1 exhibits less total acid sites and high Br?nsted to Lewis ratio.All these are beneficial to the less coke yield and higher gasoline yield.As addition amounts of F127 template in the preparation process of Y zeolite increased,the mesoporous volumes of zeolites become high and then low.When F127/SiO2 = 0.0005,the mesoporous volume of F-MUSY2 is the largest,reaching to 0.323cm3·g-1,which is higher than that of USY2 of 0.167cm3·g-1.Depend on the large total acid sites and the abundant mesostructure,F-MUSY2 shows excellent performance in catalytic cracking process.The MA value of F-MCAT2 catalyst even reaches 69.94%,which is higher by 3.89% than that without template catalyst CAT2.Hierarchical zeolite PC-MZY2 and FC-MZY2 is also prepared using copolymer(F127 or P123)and cationic surfactant CTAB as co-templates through a zeolite precursor with low ratio of silicate to aluminium.The XRD of the PC-MZY2(FC-MZY2)and PC-MUSY2(FC-MUSY2)zeolites indicate the templates have a negligible damaging effect on the framework of zeolite Y.SEM images of zeolites show that templates have slightly effect on the size and morphology of zeolites.Textural properties analysis shows that mesoporous zeolite Y prepared using co-templates does not exhibit a notly larger mesoporous volume,compared to F127 or P123.While,the total acid amount of PC-MUSY2 and FC-MUSY2 are less than single template zeolite(P-MUSY2-B or F-MUSY2-I),and the co-templates catalyst shows a lower micro-activity comparing to single template catalyst(P-MCAT2-B or F-MCAT2-I).