Study On Morphology Modification Of SAPO-11 And Its Catalytic Isomerization Performance Of Long Chain Alkanes

SAPO-11 is an important active component of hydroisomerization catalyst for increasing octane number of gasoline and decreasing pour point of lubricating oil and diesel oil.Therefore,the high activity and selectivity of SAPO-11 in isomerization reactions are the research targets of high performance catalysts.Based on the regulation of morphology and structure of SAPO-11,this paper systematically investigated the effects of ratio and methods in the process of synthesis,and the formation process of zeolites with shortened channel length as well as the catalytic performance of SAPO-11 in n-tetradecane hydroisomerization.The main results obtained are as follows:1.A series of well-crystallized SAPO-11s were synthesized by conventional hydrothermal method.It was found that the high stability of unit cell in SAPO-11 can be maintained with higher SiO₂/Al₂O₃ ratio,H₂O/Al₂O₃ ratio and lower P₂O₅/Al₂O₃ratio.Preliminary studies suggested that this phenomenon was related to the degrees of spatial distortion during calcination process,which caused by the strong interaction between the templating agent and the P atom in framework positions.2.The phenomenon of preferential growth in SAPO-11 was found by adjusting the H₂O/Al₂O₃ ratio during the conventional hydrothermal synthesis process.XRD,SEM and TEM results showed that the SAPO-11 grew along the a-axis under the high H₂O/Al₂O₃ ratio,that is,the one-dimensional elliptical pores are shortened accordingly.It was preliminarily believed that the concentration of the template leaded to different growth rates of different crystal planes during the synthesis process.Moreover,the oriented SAPO-11obtained higher reactivity and selectivity of multi-branched isomers in the isomerization of n-tetradecane,which were deemed to the reason that the shorter channel length and more pore mouth amount were beneficial for the contact probability of the active sites and could facilitate the processes through the keylock mechanism.3.MW-SAPO-11 was synthesized by microwave treatment.Though unlike the HTS-SAPO-11 samples,the MW-SAPO-11 had no obvious preferential-growth trend under different H₂O/Al₂O₃ ratio,it is worth mentioning that MW-SAPO-11 was composed of small-grained spherical aggregates with mesoporous structure.In particular,it was found that the way of Si atoms incorporating into the AlPO₄-11 framework was different from the traditional process.And the characterizations revealed the substitution obeying the SM2 and SM3 cooperative mode could realize the aggregation of“Si”species on the surface,which would show the enrichment of weak acid.It was deduced to be related to the thermal and non-thermal effects of microwave.