Synthesis And Performance Of SAPO-5/11 Intergrowth Zeolite Used By Isomerization

SAPO-11 and SAPO-5 molecular sieves are acidic components commonly used in hydroisomerization catalysts.The former shows higher isomerization selectivity,but lower multi-branched isomers content with higher octane number;while the latter shows the opposite result to SAPO-11.Combining the strength of them provides an ideal approach to develop an isomerization catalyst with high efficient performance.Therefore,SAPO-5/11 intergrowth molecular sieve was prepared in this paper,so that the catalytic performance could be improved.The feasibility of synthesizing SAPO-5/11 intergrowth molecular sieve with single template or dual template was investigated using hydrothermal method.The results showed that the pure molecular sieve with higher crystallinity was obtained with single template.SAPO-5/11 with controlled crystal phase ratio was obtained with dual template: DPA(di-npropylamine)+ TEA(triethylamine),DIPA(diisopropylamine)+ TEA.It contained two types of microporous structures,and the acid properties,especially Lewis acid distribution varied with the crystal phase ratio.The formation of independent crystal phases was inhibited with dual template of DPA and TEA.In order to optimize the physicochemical properties of SAPO-5/11 molecular sieve,the feature of inergrowth molecular sieve prepared via dry gel conversion method was investigated,and a comparison was made with that of molecular sieve prepared via hydrothermal method.The results showed that both methods could be used to synthesize SAPO-5/11 intergrowth molecular sieve with controlled crystal phase ratio.However,the former one could effectively reduce the particle size,increase the surface area,and provide a extended range to regulate the acidity distribution..Therfore,the dry gel conversion method was more favorable to regulate the properties of intergrowth molecular sieve with different crystal phasesNickel-based hydroisomerization catalysts were prepared with obtained aluminophosphate molecular sieves,and their isomerization performance was investigated using n-hexane as the model reactants.The results indicated that the intergrowth molecular sieve exhibited higher multi-branch isomers selectivity than pure-phased SAPO-11 and lower initial cracking activity than SAPO-5.Increasing the content of SAPO-5 in the intergrowth molecular sieve could increase the isomerization selectivity and the selectivity to multibranched isomers.It can be seen that the SAPO-5/11 intergrowth molecular sieve had better n-hexane isomerization performance than pure-phased molecular sieve by making use of the strength of each component.