Synthesis And Characterization Of Silicalite-1Zeolite And Zeolite Membranes

Zeolite membranes have a lot of advantages such as regularity, preciselydefined channel structures, controllable catalysis-based characteristics, thermalstability and chemical stability, making them have wide applications in chemicalseparations, membranes catalysis, microreactors and microelectronic devices etc.Thus, in the past two decades, zeolite membranes are considered as one of themost potential inorganic membrane materials and have become one of theresearch hotspots. MFI-type zeolite membranes, especially silicalite-1membrane (Si/Al�'∞), have been studied extensively due to their well-definedpore structure, shape-selective catalysis performance, strong mechanicalstrength, thermal stability and chemical stability. Silicalite-l membrane withhydrophobicity, could be applied to separation of many industrial hydrocarbonmolecules and organic/water mixtures by pervaporation.In my paper, we explored the factors on the synthesis of zeolites andgrowth of zeolites membranes on the alumina supports by in-situ hydrothermal synthesis with low basicity solution. Base on the above, a novel method, called“Pre-coating dry-gel hydrothermal synthesis technique”, was designed tosynthesize silicalite-1zeolite membrane. Scanning electron microscopy (SEM)and X-ray diffraction (XRD) were used respectively to characterize themorphology and thickness of the MFI layers and crystallographic structure. Thedetails are as following:1. The Silicalite-1zeolites were prepared by hydrothermal synthesistechnology. The effects of crystallization temperature, crystallization time, theconcentration of TPAOH and C2CH5OH in the synthesis solution wereinvestigated and optimized. The results show that the gel composition ofn(TEOS): n(TPAOH): n(H2O)=1:0.18:100, crystallization time of12hours,synthesis temperature of130℃,the obtained silicalite-1zeolites have highercrytallinity, fewer twins and the size of about500nm. Moreover, the addedalcohol has the adverse impact on the forming of the silicalite-1zeolites withhigher crytallinity and smaller size.2. The Silicalite-1zeolite membranes were prepared using the hydrothermalsynthesis method. Several effective support kinds, hydrothermal synthesisconditions, materials species and hydrothermal synthesis numbers wereinvestigated. According to the characterization results of membranes, thesuitable synthetic conditions of MFI membranes are as following: the silica sol as silica source, the TPABr as the structure directing agent and the molarcomposition of the synthesis solution of n(Na2O):n(TPA+):n(SiO2):n(H2O)=0.1:0.1:1:100, hydrothermal synthesis was carried out under static conditions at170℃for48h, we obtained the various zeolite membranes with the bettermorphology. The prepared zeolite membranes by hydrothermal synthesis of apreviously anodic oxidation pre-treatment are more homogeneous. We couldincrease the hydrothermal synthetic number to develop the growth of themembrane.3. Based on the above details, a novel fabrication method of the Silicalite-1zeolite membranes, called “Pre-coating dry-gel hydrothermal synthesistechnique”, was designed and produced. The effects of crystallizationtemperature, crystallization time, synthetic liquid alkalinity, support types, thenumber of pre-coating dry-gel on structures and properties of membranes wereinvestigated and optimized. The results show that the number of pre-coatingdry-gel of3times, the crystallization time of6hours, synthesis temperature of130℃, a highly continuous, fully covered and well flat films without any voidsare anchored on the surface of aluminum by the technique, which is a new,reasonable and suitable for industrial preparation of zeolite membranestechnique.