Easy fabrication of dense ceramic membrane for oxygen separation

A combined EDTA-citrate complexing method was developed for the easy preparation of mixed oxygen-ionic and electronic conducting dense ceramic membrane for oxygen separation. The nea method takes the advantage of lower calcination temperature for phase formation. lower membrane sintering temperature and higher relative density over the standard ceramic method.

Investigation of ideal zirconium-doped perovskite-type ceramic membrane materials for oxygen separation

Zirconium-doped perovskite-type membrane materials of BaCo0.4Fe0.6-xZrxO3-delta (x = 0-0.4) with mixed oxygen ion and electron conductivity were synthesized through a method of combining citric and EDTA acid complexes. The results of X-ray diffraction (XRD), oxygen temperature-programmed desorption (O-2-TPD) and hydrogen temperature-programmed reduction (H-2-TPR) showed that the incorporation of proper amount of zirconium into BaCo0.4Fe0.6O3-delta could stabilize the ideal and cubic structure of perovskite. Studies on the oxygen permeability of the as-synthesized membrane disks under air/He gradient indicated that the content of zirconium in these materials had great effects on oxygen permeation flux, activation energy for oxygen permeation and operation stability. The high oxygen permeation flux of 0.90 ml cm(-2) min(-1) at 950degreesC, the single activation energy for oxygen permeation in the range of 600-950 degreesC and the long-term operation stability at a relatively lower operational temperature of 800 degreesC under air/He gradient were achieved for the BaCo0.4Fe0.4Zr0.2O3-delta material. Meanwhile, the effect of carbon dioxide on structural stability and oxygen permeability of this material was also studied in detail, which revealed that the reversible stability could be attained for it. (C) 2002 Elsevier Science B.V. All rights reserved.

Performance of a mixed-conducting ceramic membrane reactor with high oxygen permeability for methane conversion

A mixed-conducting perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCFO) ceramic membrane reactor with high oxygen permeability was applied for the activation of methane. The membrane reactor has intrinsic catalytic activities for methane conversion to ethane and ethylene. C-2 selectivity up to 40-70% was achieved, albeit that conversion rate were low, typically 0.5-3.5% at 800-900 degreesC with a 50% helium diluted methane inlet stream at a flow rate of 34 ml/min. Large amount of unreacted molecular oxygen was detected in the eluted gas and the oxygen permeation flux improved only slightly compared with that under non-reactive air/He experiments. The partial oxidation of methane to syngas in a BSCFO membrane reactor was also performed by packing LiLaNiO/gamma -Al2O3 with 10% Ni loading as the catalyst. At the initial stage, oxygen permeation flux, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation flux to reach its steady state. 98.5% CH4 conversion, 93.0% CO selectivity and 10.45 ml/cm(2) min oxygen permeation flux were achieved under steady state at 850 degreesC. Methane conversion and oxygen permeation flux increased with increasing temperature, No fracture of the membrane reactor was observed during syngas production. However, H-2-TPR investigation demonstrated that the BSCFO was unstable under reducing atmosphere, yet the material was found to have excellent phase reversibility. A membrane reactor made from BSCFO was successfully operated for the POM reaction at 875 degreesC for more than 500h without failure, with a stable oxygen permeation flux of about 11.5 ml/cm(2) min. (C) 2001 Elsevier Science B.V. All rights reserved.

Novel porous metal/ceramic membrane materials

During the past 22 months, the preparation and application of novel porous metal/ceramic membrane materials have been extensively explored in the area of membrane science and catalysis. Thus, new preparation methods and new application concepts in membrane catalysis have been developed.

Electrochemical promotion of catalysis controlled by chemical potential difference across a mixed ionic-electronic conducting ceramic membrane - An example of wireless NEMCA

A La_0.6Sr_0.4Co_0.2F_0.8O₃ mixed ionic electronic conducting (MIEC) membrane was used in a dual chamber reactor for the promotion of the catalytic activity of a platinum catalyst for ethylene oxidation. By controlling the oxygen chemical potential difference across the membrane, a driving force for oxygen ions to migrate across the membrane and backspillover onto the catalyst surface is established. The reaction is then promoted by the formation of a double layer of oxide anions on the catalyst surface. Thelectronic conductivity of the membrane material eliminates the need for an external circuit to pump the promoting oxide ion species through the membrane and onto the catalyst surface. This renders this "wireless" system simpler and more amenable for large-scale practical application. Preliminary experiments show that the reaction rate of ethylene oxidation can indeed be promoted by almost one order of magnitude upon exposure to an oxygen atmosphere on the sweep side of the membrane reactor, and thus inducing an oxygen chemical potential difference across the membrane, as compared to the rate under an inert sweep gas. Moreover, the rate does not return to its initial unpromoted value upon cessation of the oxygen flow on the sweep side, but remains permanently promoted. A number of comparisons are drawn between the classical electrochemical promotion that utilises an external circuit and the "wireless" system that utilises chemical potential differences. In addition a 'surface oxygen capture' model is proposed to explain the permanent promotion of the catalyst activity. © 2007 Springer Science+Business Media, LLC.

Aqueous Sol-gel Process for Nanocrystalline Photocatalytic Titania, Transparent Functional Coatings and Ceramic Membrane

The present thesis develops from the point of view of titania sol-gel chemistry and an attempt is made to address the modification of the process for better photoactive titania by selective doping and also demonstration of utilization of the process for the preparation of supported membranes and self cleaning films.A general introduction to nanomaterials, nanocrystalline titania and sol-gel chemistry are presented in the first chapter. A brief and updated literature review on sol-gel titania, with special emphasis on catalytic and photocatalytic properties and anatase to rutile transformation are covered. Based on critical assessment of the reported information the present research problem has been defined.The second chapter describes a new aqueous sol-gel method for the preparation of nanocrystalline titania using titanyl sulphate as precursor. This approach is novel since no earlier work has been reported in the same lines proposed here. The sol-gel process has been followed at each step using particle size, zeta potential measurements on the sol and thermal analysis of the resultant gel. The prepared powders were then characterized using X-ray diffraction, FTIR, BET surface area analysis and transmission electron microscopy.The third chapter presents a detailed discussion on the physico-chemical characterization of the aqueous sol-gel derived doped titania. The effect of dopants such as tantalum, gadolinium and ytterbium on the anatase to rutile phase transformation, surface area as well as their influence on photoactivity is also included. The fourth chapter demonstrates application of the aqueous sol-gel method in developing titania coatings on porous alumina substrates for controlling the poresize for use as membrane elements in ultrafiltration. Thin coatings having ~50 nm thickness and transparency of ~90% developed on glass surface were tested successfully for self cleaning applications.

Synthesis of NaA zeolite membrane on a ceramic hollow fiber

NaA zeolite membrane was successfully synthesized on a ceramic hollow fiber with an outer diameter of 400 mum, a thickness of 100 mum and an average pore radius of 0.1 mum. The as-synthesized membranes were characterized by XRD, SEM as well as gas permeation. A continuous C NaA zeolite membrane formed after a three-stage synthesis. The membrane thickness was similar to5 mum. Gas permeation data indicated that a relatively high quality NaA zeolite membrane formed on the ceramic hollow fiber support. (C) 2003 Elsevier B.V. All rights reserved.

Ceramic membranes for separation of proteins and DNA by in situ growth of alumina nanofibres with a nanomesh of metal oxide nanofibres

Ceramic membranes were fabricated by in situ synthesis of alumina nanofibres in the pores of an alumina support as a separation layer, and exhibited a high permeation selectivity for bovine serum albumin relative to bovine hemoglobin (over 60 times) and can effectively retain DNA molecules at high fluxes.

High-flux ceramic membranes with a nanomesh of metal oxide nanofibers

Traditional ceramic separation membranes, which are fabricated by applying colloidal suspensions of metal hydroxides to porous supports, tend to suffer from pinholes and cracks that seriously affect their quality. Other intrinsic problems for these membranes include dramatic losses of flux when the pore sizes are reduced to enhance selectivity and dead-end pores that make no contribution to filtration. In this work, we propose a new strategy for addressing these problems by constructing a hierarchically structured separation layer on a porous substrate using large titanate nanofibers and smaller boehmite nanofibers. The nanofibers are able to divide large voids into smaller ones without forming dead-end pores and with the minimum reduction of the total void volume. The separation layer of nanofibers has a porosity of over 70% of its volume, whereas the separation layer in conventional ceramic membranes has a porosity below 36% and inevitably includes dead-end pores that make no contribution to the flux. This radical change in membrane texture greatly enhances membrane performance. The resulting membranes were able to filter out 95.3% of 60-nm particles from a 0.01 wt % latex while maintaining a relatively high flux of between 800 and 1000 L/m2·h, under a low driving pressure (20 kPa). Such flow rates are orders of magnitude greater than those of conventional membranes with equal selectivity. Moreover, the flux was stable at approximately 800 L/m2·h with a selectivity of more than 95%, even after six repeated runs of filtration and calcination. Use of different supports, either porous glass or porous alumina, had no substantial effect on the performance of the membranes; thus, it is possible to construct the membranes from a variety of supports without compromising functionality. The Darcy equation satisfactorily describes the correlation between the filtration flux and the structural parameters of the new membranes. The assembly of nanofiber meshes to combine high flux with excellent selectivity is an exciting new direction in membrane fabrication.