The present study investigates the formation of silicalite-1 seed layers on a porous carbon support of 0.5 μm pore size and α-A12O3 supports with different pore sizes (0.1 μm and 4 μm) via the slip-casting technique. The effects of support property, seed size and solvent on the formation of seed layers were investigated in detail. The growth of silicalite-1 membranes on different seeded supports by hydrothermal synthesis was also evaluated. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterizations indicate that a continuous seed layer can be obtained on the smooth support of 0.1 μm pore size by using any seed of 100 nm, 600 nm or 2.2 μm in size, whereas, on the coarse supports with either 0.5 μm or 4 μm pore size, a continuous seed layer cannot be formed using the above seed sizes and the same seeding time. At a longer contact time, a seed layer can also be formed using 100 nm seed on the supports with larger pore size. However, the layer is not uniform and smooth. For a hydrophobic porous carbon support, seeding ethanol suspension, which has weak polarity, favors the formation of a continuous seed layer. The seed layers and membranes grown from the smaller seed are more uniform and continuous and possess smoother surfaces than those from the larger seed. The seed layer and respective grown membrane formed from nanosized seed (100 nm) are the most uniform and compact. With this method of seeded secondary synthesis of zeolite membranes, the quality of a membrane mainly depends on the quality of the seed layer.

Factors affecting the formation of zeolite seed layers and the effects of seed layers on the growth of zeolite silicalite-1 membranes

Zeolites posses a high stability, high specific surface area and pores tridimensional system that make them useful to formation of inorganic membranes. During membranes synthesis different parameters should be considered such as nature substrate and the method used in order to obtain a membrane according to its application field. In the present work the formation of a zeolitic layer on the functionalized surface of zirconia substrates was studied. Zirconia disks of ten millimeters of diameter were prepared. They were submitted a chemical functionalization with three different chemical linkers: polyethylenimine (PEI), polydialildimethylamine chloride (PDDA) and 3-aminopropyltriethoxysilane (γ-APS). Subsequently the substrates were submitted to a seeding process, where their surface was grafted with zeolitic crystals corresponding to W zeolite. In order to promote the formation of zeolitic layer the substrates were submitted a hydrothermal treatment with a batch composition similar to that used in the W zeolite synthesis, at 150°C for 48 h. The crystallization products were characterized by XRD and SEM techniques. The results indicated that the chemical linker enhances the formation of a homogeneous zeolitic layer on the substrate and besides acts as structural directing agent allowing to crystallization of a different zeolitic phase to that used in the seeding process, the merlinoite. The morphology, crystalline phase and thickness of zeolitic layer formed on the surface of the substrate depend of the nature of chemical linker used and its interaction with the substrate.

Effect of Nature Chemical Linker on the Formation of a Zeolitic Layer on Zirconia Substrates

Good quality MFI type zeolite membranes were prepared on mesoporous Y2O3 doped ZrO2 (YZ) support and macroporous a-Al2O3 support with pure SiO2 precursor by hydrothermal process. Permeation of binary mixture H2/n-C4H10 through zeolite membranes on YZ and a-Al2O3 supports was measured using a multi-component gas permeation set-up. YZ supported zeolite membrane had a much higher n-C4H10 permeance than the a-Al2O3 supported one in the lower temperature range. The maximum n-C4H10 to H2 separation factor of YZ supported zeolite membrane was as high as 500. Pure p-xylene pervaporation through these zeolite membranes was also conducted to study the membranes separation property. The pervaporation flux declined significantly with time for the a-Al2O3 supported zeolite membrane. Much less change in pervaporation flux was found for the YZ supported zeolite membrane. XRD was employed to analyze the phase structure of the zeolite membranes. The thermal stability of the YZ and a-Al2O3 supported MFI zeolite membranes was studied by comparing the phase structure of the zeolite films after heat-treatment at different temperatures. The zeolite membrane on the YZ support remained in the MFI structure up to 1000C. The zeolite membrane on the a-Al2O3 support transformed completely to a quartz phase after heat-treatment at 950C. Zirconia supported MFI type zeolite membrane is more hydrophobic, thermally stable and fouling resistant than the alumina supported one.

Zirconia and Alumina Supported MFI Zeolite Membranes: Effects of Support Materials on Membrane Properties

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Zirconia and Alumina Supported MFI Zeolite Membranes: Effects of Support Materials on Membrane Properties