Preparation,Characterization And Applications Of Hydrocarbon Hydroisomerization Catalysts

At present,hydroisomerization of hydrocarbons is an important process to produce clean and high-octane vehicle gasoline blending component,and the hydroisomerization of hydrocarbons is usually performed over metal-acid bi-functional catalysts.Pore structure and acid property of the catalyst support are the key factors influencing the isomerization performance of the catalyst.With the aim of obtaining a catalyst with enhanced hydroisomerization performance especially the high selectivity to di-branched isomers with high octane numbers,this thesis focuses on the following two aspects:the modification of ZSM-5 and the synthesis of SAPO-11 with stronger acidity and hierarchical micro-mesoporous structure,both being widely used hydroisomerization catalyst supports in the petroleum processing industry.In the first part of this thesis,the modification of a commercial ZSM-5 zeolite by the combined use of desilication,dealumination and acid leaching in different sequences was carried out to modulate its pore structure and acidity.It was found that a modified ZSM-5 sample with abundant mesopores and moderate acidity could be obtained through the sequential desilication,dealumination,and acid leaching treatments.This ZSM-5 derived catalyst exhibited the best performance in hydro-upgrading a real fluid catalytic cracking(FCC)naphtha,resulting in the dramatically decreased olefin content and well preserved octane number of the product FCC naphtha.The remarkably enhanced catalytic performance of the ZSM-5 derived catalyst can be attributed to the following factors:(1)its moderate acidity favors the hydroisomerization reaction of olefins;and(2)the hierarchical micro-mesopore structure accelerates the diffusion of the reactants and products and thus lessens the catalyst coking.In the view of large crystal size,low acidity and small external surface area of conventional SAPO-11 molecular sieve,a SAPO-11 molecular sieve with smaller size,hierarchical pore structure and strong acidity was successfully synthesized by introducing a cationic surfactant cetyltrimethylammonium bromide(CTAB)and a nonionic copolymer Pluronic F127(F127)into the synthetic system.It was found that CTAB functioned as an acidity promoter of SAPO-11 and a mesoporogen to direct the formation of intracrystalline mesopores in SAPO-11,while F127 functioned as a crystal growth inhibitor to control the morphology and thus avoid the further growth of SAPO-11 crystals.Thanks to the enhanced acidity and the increased exposed pore mouths due to the decreased crystal size and the increased external surface area,this SAPO-11 supported catalyst exhibited outstanding performance in n-octane hy droi somerizati on.To further increase the utilization ratio of SAPO-11 molecular sieve,the third part of this thesis presents a novel approach to synthesize an alumina@SAPO-11 composite with core-shell structure.The composite is featured by that the SAPO-11 phase in the shell has bimodal mesoporosity.This approach was achieved by the anchoring of the SAPO-11 precursors on a H3PO4 modified alumina substrate and the in-situ assembly of the resulting SAPO-11 nanoclusters.Compared with the catalyst supported on a mechanic mixture of SAPO-11 and H3PO4 modified alumina,the alumina@SAPO-11 supported Pt catalyst displayed dramatically enhanced n-octane hydroisomerization performance.This is mainly attributed to that:(1)the abundant mesopore structures in the composite can shorten the residence time of the formed intermediates in the catalyst and thus lessens their cracking;and(2)the highly exposed micropore mouths favor the production of di-branched isomers.The methodology presented in this thesis provides a novel and simple approach which extends the preparation method of catalyst support effectively.