Ceramic macromembrane for tangento-axial micro- and ultrafiltration water systems

An innovative proposal of tangento-axial filtration based on the concept of macromembrane (large size) is presented in the context of micro- and ultrafiltration ceramic membranes. The macromembrane is made of Al2O3–TiO2 by slip casting. It includes an internal system for rotating the fluid trough a propeller which enhances the tangento-axial filtration. This filtration yields better than the cross-flow filtration in conventional extruded ceramic tubes of small diameter. The reasons are, first, its larger sizes relative to the extruded tubular filters, and second, that it can work at higher pressures, resulting in better operational performance. Furthermore, costs of industrial-scale production could be lower. In this study, the conceptual basis, pilot plant, first experimental results, and proposals for improvement of the system to continue the project are presented.Peer ReviewedPostprint (author's final draft

Pore Narrowing and Formation of Ultrathin Yttria-Stabilized Zirconia Layers in Ceramic Membranes by Chemical Vapor Deposition/Electrochemical Vapor Deposition

Chemical vapor deposition (CVD) and electrochemical vapor deposition (EVD) have been applied to deposit yttria-stabilized-zirconia (YSZ) on porous ceramic media. The experimental results indicate that the location of YSZ deposition can be varied from the surface of the substrates to the inside of the substrates by changing the CVD/EVD experimental conditions, i.e., the concentration ratio of the reactant vapors. The deposition width is strongly dependent on the deposition temperature used. The deposition of YSZ inside the pores resulted in pore narrowing and eventually pore closure, which was measured by using permpor-ometry. However, deposition of YSZ on top of porous ceramic substrates (outside the pores) did not result in a reduction of the average pore size. Ultrathin, dense YSZ layers on porous ceramic substrates can be obtained by suppressing the EVD layer growth process after pore closure

Effect of the anodization voltage on the porewidening rate of nanoporous anodic alumina

A detailed study of the pore-widening rate of nanoporous anodic alumina layers as a function of the anodization voltage was carried out. The study focuses on samples produced under the same electrolyte and concentration but different anodization voltages within the self-ordering regime. By means of ellipsometry-based optical characterization, it is shown that in the porewidening process, the porosity increases at a faster rate for lower anodization voltages. This opens the possibility of obtaining three-dimensional nanostructured nanoporous anodic alumina with controlled thickness and refractive index of each layer, and with a refractive index difference of up to 0.24 between layers, for samples produced with oxalic acid electrolytes

Low-cost ceramic membranes: A research opportunity for industrial application

Obtaining low-cost ceramic membranes has attracted great interest in the scientific community in last years, as it allows to preserve the advantages of ceramic materials while significantly reduce their manufacturing costs. This type of membranes is mainly based on the use of raw materials and manufacturing processes typical of traditional ceramic materials, i.e silicate-based ceramics. This work exhaustively reviews the raw materials, ceramic compositions and variables of the manufacturing processes used in the development of these membranes, with special emphasis on their numerous potential industrial applications

Modelling and analysis of CVD processes for ceramic membrane preparation

A mathematical model is presented that describes the modified chemical vapour deposition (CVD) process (which takes place in advance of the electrochemical vapour deposition (EVD) process) to deposit ZrO2 inside porous media for the preparation and modification of ceramic membranes. The isobaric model takes into account intrapore Knudsen diffusion of ZrCl4 and H2O, which enter the membrane from opposite sides, and Langmuir-Hinshelwood reaction of the solid product ZrO2 on the internal pore wall. The processes occurring in one single pore are investigated, and the change in pore geometry during deposition is taken into account. Based upon this model, the deposition profile is studied. The model fits reasonably well with experimental results

Preparation of tubular alumina-based membranes incorporated with coal fly ash and application as support to ZSM-5 membranes

Synthetic membranes are increasingly used in different applications for the concentration, fractionation, and efficient purification of components present in solutions and mixtures of liquids or gases. Ceramic membranes have a large potential over the polymeric ones for applications at high temperature, pressure, and in aggressive environments. However, the preparation of ceramic membranes is expensive. The coal fly ash (CFA) is a burning coal byproduct with structural qualities, mainly composed of silica and alumina oxides, being an appropriate and inexpensive raw material for ceramic membrane addition. Thus, the main objective of this work is to prepare and characterize tubular alumina-based membranes incorporated with CFA, without additive and binder-free, using the centrifugal casting method. In addition, this work aims to use these ceramic membranes as support for the ZSM-5 zeolites prepared without using organic structure-directing agents for application in catalytic processes. The centrifugal casting method with high-speed mold rotation has produced asymmetric membranes with different morphologies at the inner and outer surfaces of the tubes. High CFA fraction in the membranes resulted in higher porosity levels and water permeability, accompanied by a decrease in mechanical strength and in linear shrinkage. Moreover, the observed permeate flux was in the range between 116 and 370 L m-2 h-1 bar-1, and the retention for the cornstarch solution was above 99 % for all the membranes. To test the zeolitic deposition on these tubes, the synthesis of the ZSM-5 zeolite was performed with a theoretical Si/Al ratio of 50. The ZSM-5 zeolite membranes could be successfully synthesized on the tubes using the seeding method followed by the direct hydrothermal synthesis. The prepared materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy and tested for The prepared materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy and tested for separation of organic compounds and xylene isomerization reaction. The ceramic membranes CFA-based showed potential application for wastewater treatment and can be used as support to selective layer coatings as the ZSM-5 zeolite.Les membranes synthétiques sont de plus en plus utilisées dans différentes applications pour la concentration, le fractionnement et la purification efficaces des composants présents dans les solutions, ainsi que dans les mélanges de liquides ou de gaz. Les membranes céramiques ont un grand potentiel par rapport aux membranes polymères pour des applications à haute température, à haute pression et dans des environnements agressifs. Cependant, la préparation des membranes céramiques est coûteuse. La cendre volante de charbon (CFA, de l'anglais coal fly ash) est un sous-produit de la combustion du charbon dont les qualités structurelles, principalement composées d'oxydes de silice et d'alumine, sont une matière première appropriée et peu coûteuse qui peut être ajoutée à des membranes céramiques. Ainsi, l'objectif principal de ce travail est de préparer et de caractériser des membranes tubulaires à base d'alumine incorporées avec la CFA, sans additif et sans liant, en utilisant la méthode de coulée centrifuge. En outre, ce travail vise à utiliser ces membranes céramiques comme support pour les zéolithes ZSM-5 préparées sans utiliser d'agents organiques directeurs de structure pour les procédés catalytiques. La méthode de coulée par centrifugation avec rotation du moule à grande vitesse a produit des membranes asymétriques de morphologies différentes sur les surfaces intérieures et extérieures des tubes. La fraction élevée de CFA dans les membranes a entraîné des niveaux de porosité et une perméabilité à l'eau plus élevée, accompagnés d'une diminution de la résistance mécanique et du retrait linéaire. De plus, le flux de perméat observé était compris entre 116 et 370 L m-2 h-1 bar-1, et la rétention pour la solution d'amidon de maïs était supérieure à 99 % pour toutes les membranes. CPour tester le dépôt zéolitique sur ces tubes, la synthèse de la zéolite ZSM-5 a été réalisée avec un rapport théorique Si/Al de 50. Les membranes de la zéolite ZSM- 5 ont pu être synthétisées avec succès sur les tubes en utilisant la méthode d'ensemencement suivie de la synthèse hydrothermale directe. Les matériaux préparés ont été caractérisés par la diffraction des rayons-X, la spectroscopie infrarouge à transformée de Fourier et la microscopie électronique à balayage et ils ont été testés pour la séparation des composés organiques et la réaction d'isomérisation du xylène. Les membranes céramiques à base de CFA ont montré une application potentielle pour le traitement des eaux usées et peuvent être utilisées comme support pour le dépôt des couches de catalyseur comme la zéolite ZSM-5

Mixed-conducting LSC/CGO and Ag/CGO composites for passive oxygen separation membranes

Dense ceramic oxygen separation membranes can pass oxygen perm-selectively at elevated temperature and have potential for improving the performance and reducing the cost of several industrial processes: such as the conversion of natural gas to syngas, or to separate oxygen from air for oxy-fuel combustion in electricity generation (to reduce NOx emissions and facilitate CO2 sequestration). These pressure-driven solid state membranes are based on fast oxygen-ion conducting ceramics, but also need a compensating flow of electrons. Dual-phase composites are attractive since they provide an extra degree of freedom, compared with single phase membranes, for optimising the overall membrane performance. In this study, composites containing gadolinia doped ceria (CGO, Ce0.9Gd0.1O2- ) and either strontium-doped lanthanum cobaltite (LSC, La0.9Sr0.1CoO3- or La0.6Sr0.4CoO3- ) or silver (Ag) were investigated for possible application as oxygen separation membranes in oxy-fuel combustion system. These should combine the high oxygen ion conductivity of CGO with the high electronic conductivity and fast oxygen surface exchange of LSC or silver. Dense mixed-conducting composite materials of LSC/CGO (prepared by powder mixing and sintering) and Ag/CGO composites (prepared by silver plus copper oxide infiltration method) showed high relative density (above 95%), low background gas leakage and also good electrical conduction. The percolation threshold of the electronic conducting component was determined to be approximately 20 vol.% for both LSC compositions and 14 vol.% for Ag. Isotopic exchange and depth profiling by secondary ion mass spectrometry was used to investigated the oxygen tracer diffusion (D*) and surface exchange coefficient (k*) of the composites. Composites just above the electronic percolation threshold exhibited high solid state oxygen diffusivity, fast surface exchange activity moderate thermal expansion and sufficient mechanical strength thus combining the benefits of their constituent materials. The preliminary work on oxygen permeation measurement showed that the reasonable magnitude of oxygen fluxes is possible to be achieved. This indicates that the composites of LSC/CGO and Ag/CGO are promising for further development as passive oxygen separation membranes

Development of porous alumina membranes for treatment of textile effluent

Published online: 27 Feb 2015Ceramic porous membranes sintered at two different temperature using polyvinyl alcohol and ethylene glycol as binders, and composed of two types of α-alumina with different particle sizes were investigated for the microfiltration of a textile effluent containing indigo dye, auxiliaries, heavy metals, oils, and solids. The physicochemical properties of the membranes and effluent were evaluated. X-ray diffraction, energy dispersive X-ray fluorescence spectroscopy, differential scanning calorimetry, and thermogravimetric analysis confirm that the thin membrane is composed of high crystalline and pure α-alumina. Scanning electron microscopy observation indicates that the membranes have smooth porous surface making it suitable for microfiltration applications. The membrane sintered at 1,450˚C exhibited higher water absorption (WA) and apparent porosity than that sintered at 1,475˚C. The apparent specific gravity and flexural strength are in inverse correlation with the WA due to the enhanced densification of the membranes. The filtered effluent was evaluated using a membrane with an average pore size of 0.4 μm and a total porosity of 29.6%. The average values of rejection were 90% for color, 93% for suspended solids, 95% for turbidity, 60% for metals, and 73% for chemical oxygen demand. These results demonstrate that low-cost ceramic alumina membranes are a very promising advanced treatment for textile industrial effluents.Andrea Zille (C2011- UMINHO-2C2T-01) acknowledges funding from Programa Compromisso para a Ciencia 2008, Portugal

An initial investigation of a nano-composite silica ceramic membrane for hydrogen gas separation and purification.

The effects of trans-membrane pressure difference on hydrogen recovery are investigated on a preliminary basis. The membrane has been developed for high temperature hydrogen separation from CH4, N2, and Ar gas molecules. Gas permeation and separation performance of the developed membrane was evaluated. The silica fabricated membrane exhibited high H2 gas flux and much lower fluxes for CH4, N2, and Ar and showed a rise in permeance with the inverse of the square root of temperature for H2. Plots obtained with respect to the effects of gauge pressure on H2, N2, CH4 and Ar component gas fluxes through the modified support (silica membrane) at a pressure of 1 bar showed that H2 recorded an almost four-fold high flux value of 0.76 mol/m2.s compared to that of 0.33 mol/m2.s (CH4), 0.25 mol/m2.s (N2) and 0.22 mol/m2.s (Ar). These results were nearly stable for the temperature range investigated (298 K, 373 K and 473 K). In addition, hydrogen maintained a relatively high permeance value of 1.62 × 10-5 mol m-2 s-1 Pa-1 at a low pressure of 0.1 bar under room temperature (298 K) compared to that of N2, CH4 and Ar which were much lower throughout the temperature range studied and in agreement with literature. H2 separation factor (experimental Knudsen) over CH4, N2 and Ar were quite close to the theoretical Knudsen and can therefore be experimentally applied through further optimization in the separation of H2 as a key constituent energy for the future