Structure–Property Relationships of Inorganically Surface-Modified Zeolite Molecular Sieves for Nanocomposite Membrane Fabrication (original) (raw)
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The Canadian Journal of Chemical Engineering, 2012
Zeolite molecular sieves are essential to many processes in adsorption, catalysis and ion exchange. From the separation of air, to petroleum cracking, to water softening and decontamination, these materials influence our everyday lives. Some researchers have come to believe that all the great discoveries in the field of molecular sieves may be in the past. Nothing could be farther from the truth. From new mechanisms for pore size control, to new nanocomposite materials, to approaching the dream of robust, industrial-scale sieving membranes, to whole new definitions for molecular sieves, new forms and uses of these materials are rapidly evolving.
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Science, 2003
A seeded growth method for the fabrication of high-permeance, high-separation-factor zeolite (siliceous [Si 96 O 192 ]-MFI) membranes is reported. The method consists of growing the crystals of an oriented seed layer to a well-intergrown film by avoiding events that lead to a loss of preferred orientation, such as twin overgrowths and random nucleation. Organic polycations are used as zeolite crystal shape modifiers to enhance relative growth rates along the desirable out-of-plane direction. The polycrystalline films are thin (ϳ1 micrometer) with single grains extending along the film thickness and with large in-plane grain size (ϳ1 micrometer). The preferred orientation is such that straight channels with an open diameter of ϳ5.5 angstroms run down the membrane thickness. Comparison with previously reported membranes shows that these microstructurally optimized films have superior performance for the separation of organic mixtures with components that have small differences in size and shape, such as xylene isomers.
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This is a comprehensive review of the recent progresses made in the field of zeolite membranes. It describes zeolitic materials and methods of membrane fabrication, followed by a summary of applications for gas separation, pervaporation and separation of liquid mixtures. Special attention is called to polymer mixed matrix membranes (MMMs) and membranes based on metal organic frame works (MOFs). In this comprehensive survey, the following trends were observed during the past 5 – 10 years. New zeolitic materials and new synthesis methods, such as hydrothermal synthesis, seeding and microwave heating, have been continuously reported in the literature. Many efforts have been devoted to the synthesis of hybrid or mixed matrix membranes (MMMs) since MMMs clearly outperformed polymeric membranes. MOFs also showed improved performance in gas separation. Many attempts have been made to develop thin (1µm) supported zeolite layers on a variety of carriers such as capillaries, fibers, tubes, et...
Journal of Materials Chemistry, 2001
Zeolite Beta/MCM-41 composites have been prepared with various crystallinities of zeolite Beta through a twostep crystallization process involving the combination of low crystallinity zeolite Beta synthesis gel with cetyltrimethylammonium bromide surfactant solution. The composites are characterized by XRD, SEM, 29 Si and 27 Al MAS NMR, N 2 adsorption, NH 3-TPD and catalytic cracking. The experimental results show that the relative crystallinity of Beta in the composites greatly affects the morphology and surface acidity of the materials, while exhibiting similar 29 Si, 27 Al MAS NMR spectra and N 2 adsorption-desorption isotherms. The pore structural data indicate that the composites contain bimodal mesopore systems and microporous structures of zeolite Beta. Although the number of weak acid sites on the composites with various crystallinities of Beta is comparable, composites with higher Beta crystallinity possess more medium acid sites and show higher catalytic activity for n-heptane cracking.
SYNTHESIS AND CHARACTERIZATION OF NANO ZEOLITE LTL MEMBRANE
Abstract: Zeolites are microporous crystalline materials with uniform-shaped pores of molecular dimensions. Recently, nanosized zeolites have drawn much attention for their novel applications, for example, as the seed of thin film, hosts of photo chemically or optically active guests, drug delivery carriers, etc. Zeolite LTL nano size was synthesized with the average sized about 100 nm.
Optimization of conditions for the preparation of zeolite HS membrane
Effects of synthesis parameters on the membrane structure and performance have been investigated for Nano pore Hydroxysodalite (HS) zeolite membranes grown onto seeded mullite supports. Molar composition of the starting gel of HS zeolite membranes was SiO2/Al2O3=1.0-5.0, Na2O/Al2O3=15-65, and H2O/Al2O3=500-1500. In addition, Effects of crystallization time and temperature on the membrane performance were studied. X-ray diffraction (XRD) patterns of the membranes exhibited peaks corresponding to the support and the zeolite. The crystal species were characterized by XRD and morphology of the supports subjected to crystallization was characterized by Scanning electron microscopy (SEM). Separation performance of HS zeolite membranes was studied for water-Ethanol mixtures using pervaporation (PV). The membranes showed good selectivity towards water in the water-Ethanol mixtures. Water permeates faster because of its preferential adsorption into the Nano-pores of the hydrophilic zeolite membrane. In PV of water-Ethanol mixtures, the membrane exhibits a hydrophilic behavior, with a high selectivity towards water and a good flux. The best Flux and separation factor of the membranes were 2.05 kg/m 2 .h and 10000, respectively. Effects of operation condition (temperature, rate and pressure) on the membrane performance have been investigated for HS zeolite membranes grown onto seeded mullite supports.