Synthesis Of SAPO-34Molecular Sieve

SAPO-34is a type of SAPO zeolites that has attracted most of the attention.Owing to the particular pore structure, adjustable acidity, good thermal andhydrothermal stability, it showed excellent performance in many reactions. Tosynthesize the SAPO-34zeolite with high purity and crystallinity, the researchershave made great effort on it. Tetraethylammonium hydroxide was one of the mostused template in the early days, but its high cost obstruct the application in industrialscale. While the cheaper template, such as morpholine, triethylamine anddiethylamine could lead to the formation of impurity and should be operate at strictconditions. So, the determination of suitable condition for the synthesis of SAPO-34is of high importance.The cheap diethylamine was employed as template to synthesis SAPO-34withhydrothermal method. The influence of silicon source, aluminium source,crystallization temperature and crystallization time was investigated, the optimumcondition was obtained as below: colloidal silica used as silicon source,pseudo-boehmite as aluminium source and the solution was crystalized at200?for24h. The Box-Behnken experimental design was adopted to study the impact of rawmaterial ratio. Pure SAPO-34with high crystallinity could be obtained atn(P2O5)/n(Al2O3), n(SiO2)/n(Al2O3) and n(DEA)/n(Al2O3)=1.0343?0.6091?2.050respectively.In addition, SAPO-5was usually an associated material in the synthesis ofSAPO-34, hence the further study of the factor that affecting the intergrowth isessential. The tetraethylammonium hydroxide and diethylamine were used as mixedtemplate to synthesize SAPO-5and SAPO-34zeolites. XRD, SEM?XRF andNH3-TPD was employed to characterize the properties of them and their performancewas tested in the styrene oxide isomerization. The results indicated that pure SAPO-5and SAPO-34could be synthesized with the same raw material ratios, only bychanging the feeding order and heating mode of crystallization. The strong acid sitesover SAPO-34would lead to the formation of heavy product and reduce theselectivity to phenylacetaldehyde, while the weakly acidic SAPO-5showed betteractivity and selectivity.