Preparation of hydrophilic silicalite-1 nanocrystal-layered membranes and their application to separating water from water–acetone solution

Separation of water from a water-acetone solution was carried out by a pervaporation method using a hydrophilic silicalite-1 membrane. Silicalite-1 nanocrystals were piled up on the outer surface of cylindrical alumina ceramic filters, followed by a hydrothermal synthesis to form a silicalite-1 protection layer oil the nanocrystal layer. In other words, the membrane consisted of a silicalite-1 nanocrystal layer and a silicalite-1 protection layer (the nanocrystal-layered membrane). In order to achieve high hydrophilic properties of the membrane with the remaining silanol group, the liquid-phase oxidation technique was applied to remove the template. From the SEM observation, the nanocrystal layer and the protection layer were clearly observed, and the silicalitc-1 protection layer was uniformly formed on the nanocrystal layer. Pervaporation experiments to separate water from the water-acetone solution were conducted using the nanocrystal-layered membrane. It was considered that the secondary growth of the nanocrystals around the interface between the nanocrystal and protection layers affected the separation properties. The effects of the nanocrystal size oil the separation properties were examined. The membrane exhibited selective permeation as well as a high flux of water, and these properties were improved with a decrease in the size of the nanocrystals. Moreover, the layered membrane exhibited high hydrophilic properties regardless of the acetone concentrations. (C) 2008 Elsevier Inc. All rights reserved

Size-Controlled Synthesis of Nano-Zeolites and Their Application to Light Olefin Synthesis

For the application of zeolites as heterogeneous catalysts, low diffusion resistance for hydrocarbons within the micropore is essential for improving product selectivity and catalyst lifetime. This problem has been overcome by reducing the crystal size. This review introduces size-controlled preparation of nano-sized zeolites via hydrothermal synthesis in water/surfactant/organic solvent (emulsion method) and their application to heterogeneous catalysts. The ionicity of the hydrophilic group in surfactant molecules and the concentration of the Si source affected the crystallinity and morphology of zeolites prepared using the emulsion method. When using a non-ionic surfactant, mono-dispersed silicalite-1 nanocrystals approximately 60 nm in diameter were successfully prepared. Nano- and macro-ZSM-5 zeolites with crystal sizes of approximately 150-200 nm and 1.5 μm, respectively, were prepared and applied to n-hexane cracking and acetone-to-olefin reactions to investigate the effect of zeolite crystal size on catalytic stability and light olefin yield. Application of nano-zeolite to light olefin production was effective in achieving faster mass transfer of hydrocarbon molecules within the micropore, which led to improvements in olefin yields and catalyst lifetime

Liquid-phase diffusivity of benzene within mesoporous materials measured by a laser Raman technique

The intracrystalline diffusivities of benzene within a series of porous materials in the liquid phase (cyclohexane was used as solvent) were measured by a constant volumetric method using Raman spectroscopy at a temperature range from 323 to 393 K. Silicalite-1, mono-dispersed mesoporous silica spheres (MMSS), Silica Gel, γ-Al2O3, and SiO2-Al2O3 were used as adsorbents. The intracrystalline diffusivity was calculated by parameter fitting using theoretical equations and the experimental transient change of benzene concentrations with time in response to the adsorption. The intracrystalline diffusivities of benzene within mesoporous silicas were almost the same as that within the micropore of silicalite-1, though the pore diameters of silicalite-1 and mesoporous silicas were different from each other. It is considered that the pore walls as well as the solvent molecules of cyclohexane affect the diffusion of benzene molecules in the meso pore region

New Method for Preparing Monodispersed Nanocrystalline Silicalite via Hydrothermal Synthesis in Water/Surfactant/Oil Solution

Monodispersed silicalite nanocrystals with a diameter of 80–150 nm were successfully prepared in water–surfactant–oil solution. It was found that the ionicity of the surfactants used in preparation affected the crystallinity and structure of the silicalite, and that silicalite nanocrystals could be obtained when using a nonionic surfactant. Furthermore, silicalite nanocrystals with a diameter of approximately 80 nm could be obtained in even a high concentration region of Si source