Study On Pore Structure Modulation Of SAOP-11 And Its Catalytic IsomerizationPerformance

SAPO-11 molecular sieve plays an important role in the isomerization of alkanes, because of its special acidity and pore strcture. The design and synthesis of high active and selective SAPO-11 is a key issue in the field. In this paper, the various factors of influencing the channel length and pore size of SAPO-11 have been systematically studied, and the catalytic activity for different channel-length SAPO-11 in the octane isomerization has also been investigated. The main results are as follows:1. The ways to increase the crystallinity of SAPO-11 and control the acidity of SAPO-11 were investigated, showing that the crystallinity and dispersion of SAPO-11 crystal was rarely influenced by the feed compositions, but highly influenced by the ways of dynamic synthesis, addition of seed, and addition patterns of HF. Besides, through the way of ammonium exchange before calcination, the amount of medium strong acid of SAPO-11 can be effectively increased.2. By adjusting the ratio of H2O/Al2O3, the phenomenon of oriented growth of SAPO-11 zeolite was discovered. XRD and SEM results showed that the increase of the ratio of H2O/Al2O3 contributes to the growth of crystal in vertical direction of C axis, and restraint its growth along the C axis, the channel direction of SAPO-11. The composition, structure, and acidity of SAPO-11 were not obviously changed in the oriented growth process. A further investigation revealed that the oriented growth of SAPO-11 was caused by the change of the concentration of the template in the system. Meanwhile, the increased catalytic activity of n-octane isomerization on SAPO-11, with decreased selectivity to the product "methyl-heptane" and increased selectivity to dimethyl-hexane, were caused by the increase of the pore mouth amount.3. After its calcination, the influences on the space groups (namely pore size) in SAPO-11 were studied. The results manifested that the stability of unit cell of SAPO-11 can be improved by increasing the SiO2/Al2O3 ratio in the molecular sieve frameworks. The way of ammonium exchange before calcination, could effectively improve the stability of Icm2 space groups. The reason is probably that the partially removal of template of SAPO-11 by the additional ammonium salt reduces the skeleton distortion during the process of calcination.