Synthesis of SAPO-35 zeolite with different template agents and its performance in methanol to olefin

A series of SAPO-35 zeolites with different SiO₂/Al₂O₃ ratio were prepared by hydrothermal synthesis using HMI and NMP as template agents. The synthesized molecular sieve samples were characterized by XRD, SEM, FT-IR, NH₃-TPD, XRF and N₂ adsorption-desorption. The results showed that the crystallinity and acid density of the zeolite increased first and then decreased with the increase of the SiO₂/Al₂O₃ ratio in the initial gel. When the SiO₂/Al₂O₃ ratio was 0.3, the sample SAPO-35-0.3(HMI) had high crystallinity, large specific surface area and suitable acid distribution. The SAPO-35-NMP sample was synthesized by using a new N-methylpiperidine (NMP) as structure guide agent based on the silica-al ratio, and the SAPO-35-0.3(HMI) molecular sieve synthesized by the same SiO₂/Al₂O₃ ratio was compared and analyzed. The results show that the catalytic stability of SAPO-35-NMP is significantly better than that of SAPO-35-HMI, and the selectivity of diene is increased to 81.3%, and the selectivity of ethylene is 45.6%, which can account for more than 50% of the selectivity of diene.