Crystallization Process of SAPO-34 Molecular Sieve Using Hydrogen Fluoride and Triethylamine as Composite Template

XRD, SEM, FT-IR, NMR and TGA were used to characterize the crystallization pro ce ss of the SAPO-34 molecular sieve synthesized using HF-triethylamine as the co mposite template. XRD results indicate that SAPO-5 molecular sieve appears at t he beginning of the crystallization and disappears gradually as the crystalliz ation continues. Pure SAPO-34 is obtained at the end of the crystallization pro cess (60 h). The presence of HF decreases the crystallization rate of SAPO-34 c ompared with the case without adding HF. SEM results show that the crystallizati on of SAPO-34 is a continual process and SAPO-34 crystals with perfect surface s are achieved at the end of the process. FT-IR results show that when the crys tallization time is 3 h, some SiO 4 tetrahedra are observed and the SAPO-34 mo lecular sieve appears. That is to say, the SAPO-34 can only be formed when Si O 4 tetrahedra are formed. NMR results indicate that the AlPO 4 structure is f i rst formed and when silicon atoms enter the structure, SAPO-34 is obtained. TG A results show that template molecules are gradually contained in the pore stru cture of SAPO-34 and at the beginning of the crystallization, the thermal deco mposition process includes the decomposition of chelated materials. SAPO-34 obt ained at 12 h already bears good catalytic performance for methanol-to-olefin and the molecular sieve samples with a longer crystallization time produce less isobutene because there is less SAPO-5 or no SAPO-5 in the samples.