Synthesis Of Zeolites With Unique Crystals:Introduction Of Mesoporosity And Formation Of Membrane

Zeolites are widely used in the field of adsorption,separation,and catalysis due to their uniform pore structure,high surface area,strong acidity,and high hydrothermal stability.With the development of the times,requirements on the property of zeolites are getting higher and higher.On this background,the conventional zeolite powder with single pore structure could not meet the need,and the synthesis of zeolites with unique crystals has become one of the research hotspots.In this paper,we do some work in this field,such as introducing mesopores into the zeolite crystals,making zeolite grow to form zeolite membranes,in-situ crystallization of kaolin microspheres,and more details are listed as follows:Mesoporous EU-1 zeolite(M-EU-1)is rationally synthesized from a starting aluminosilicate gel in the presence of small organic template(hexamethonium bromide,HMBr2)and mesoscale cationic polymer(polydiallyldimethylammonium chloride,PDADMAC).Despite much encouraging progress for mesoporous aluminosilicate zeolites with 3D channels such as ZSM-5 and Beta in recent years,the syntheses of mesoporous aluminosilicate zeolites with monodimensional channels are still scarce yet.After characterizations of the EU-1 with by XRD,N2 sorption,SEM,TEM,NMR,and TG techniques,it is shown that the sample has good crystallinity,meso/microporosity,high BET surface area(442 m2/g),and large pore volume(0.28 cm3/g).Particularly,the mesoporosity in the M-EU-1 could be adjusted by the amount of mesoscale cationic polymer added in the starting gels.Catalytic tests in m-xylene isomerization show that the M-EU-1 is more stable than the conventional EU-1 synthesized in the absence of the mesoscale template.Compact NaA zeolite membranes are successfully synthesized from direct crystallization of gel-dipped macroporous Al2O3 tubes.Most of the zeolite membrane preparations are performed under hydrothermal conditions,where the material utilization rate is very low.In this work,before the gel-dipping,NaA seeds are pasted on the Al2O3 tubes,followed by macropore-plugging with liquid.After the gel-dipping,a thin gel-layer formed on the Al2O3 tube is directly crystallized into NaA zeolite membranes at 100?for 4 h in the absence of any excess liquid.The as-synthesized NaA membranes exhibit high pervaporation performance with a remarkable separation factor larger than 10000 and high flux of 2.73 kg m-2 h-1 for dehydration of 90 wt.%ethanol at 75?.Notably,in this work,when compared with conventional hydrothermal synthesis,the usage of the raw aluminosilicate materials for successful preparation of NaA zeolite membranes is sharply reduced by almost 95%,which means this new efficient synthesis is potentially significant for preparation of high-performance,low-cost,and reproducible zeolite membranes.The direct crystallization method is expanded to the fabrication of hydrophobic pure silica MFI zeolite membranes.Compact MFI zeolite membranes with separation performance are successfully prepared from direct crystallization of gel-dipped macroporous Al2O3 tubes.Ethanol is introduced into the solvent in the synthesis gel,making a sufficient contact between MFI layer and the gel,which is beneficial for repairing tiny defects.The as-synthesized MFI membrane exhibits a separation factor larger than 23 and flux of 1.67 kg m-2 h-1 in 5 wt.%ethanol/water mixture separation at 60?.NaY/kaolin composites are prepared by dry-gel in-situ growth method.We take strict control of the amount of the Y directing agent added in the dry gel,successfully obtaining the NaY/kaolin composites which are with high crystallinity and maintain the shape of powder from macroscopic view and microsphere from microscopic view.Dry gel method increases the yield of zeolite products and reduces synthesis pressure,providing a new way to developing green synthesis of FCC catalysts.