Performance of hydrophobic and hydrophilic silica membrane reactors for the water gas shift reaction

In this study, a novel molecular sieve silica (MSS) membrane packed bed reactor (PBR) using a Cu/ZnO/Al2O3 catalyst was applied to the low-temperature water gas shift reaction (WGS). Best permeation results were H-2 permeances of 1.5 x 10(-6) mol(.)s(-1) m(-2) Pa-1, H-2/CO2 selectivities of 8 and H-2/N-2 selectivities of 18. It was shown that an operation with a sweep gas flow of 80 cm 3 min(-1), a feed flow rate of 50 cm(3) min(-1) and a H2O/CO molar ratio of one at 280 degreesC reached a 99% CO conversion. This is well above the thermodynamic equilibrium and achievable PBR conversion. Hydrophilic membranes underwent pore widening during the reaction while hydrophobic membranes indicated no such behaviour and also showed increased H-2 permeation with temperature, a characteristic of activated transport. (C) 2003 Elsevier Science B.V. All rights reserved.

Modeling hydrogen separation in high temperature silica membrane systems

In this work, a working model is proposed of molecular sieve silica (MSS) multistage membrane systems for CO cleanup at high temperatures (up to 500 degrees C) in a simulated fuel cell fuel processing system. Gases are described as having little interactions with each other relative to the pore walls due to low isosteric heat of adsorption on silica surfaces and high temperatures. The Arrhenius function for activated transport of pure gases was used to predict mixture concentration in the permeate and retentate streams. Simulation predicted CO could be reduced to levels below the required 50 ppmv for polymer electrolyte membrane fuel cell anodes at a stage H-2/CO selectivity of higher than 40 in 4 series membrane units. Experimental validation showed predicting mixture concentrations required only pure gas permeation data. This model has significant application for setting industrial stretch targets and as a robust basis for complex membrane model configurations. (c) 2006 American Institute of Chemical Engineers.

Desenvolvimento de membranas porosas de alumina para fins de tratamento de efluente industrial têxtil

Textile production has been considered as an activity of high environmental impact due to the generation of large volumes of waste water with high load of organic compounds and strongly colored effluents, toxic and difficult biodegradability. This thesis deals with obtaining porous alumina ceramic membranes for filtration of textile effluent in the removal of contaminants, mainly color and turbidity. Two types of alumina with different particle sizes as a basis for the preparation of formulation for mass production of ceramic samples and membranes. The technological properties of the samples were evaluated after using sintering conditions: 1,350ºC-2H, 1,450ºC-30M, 1,450ºC-2H, 1,475ºC-30M and 1,475ºC-2H. The sintered samples were characterized by XRD, XRF, AG, TG, DSC, DL, AA, MEA, RL, MRF-3P, SEM and Intrusion Porosimetry by Mercury. After the characterization, a standard membrane was selected with their respective sintering condition for the filterability tests. The effluent was provided by a local Textile Industry and characterized at the entry and exit of the treatment plant. A statistical analysis was used to study the effluent using the following parameters: pH, temperature, EC, SS, SD, oil and grease, turbidity, COD, DO, total phosphorus, chlorides, phenols, metals and fecal coliform. The filtered effluent was evaluated by using the same parameters. These results demonstrate that the feasibility of the use of porous alumina ceramic membranes for removing contaminants from textile effluent with improved average pore size of 0.4 micrometre (distribution range varying from 0,025 to 2.0 micrometre), with total porosity of 29.66%, and average percentages of color removal efficiency of 89.02%, 92.49% of SS, turbidity of 94.55%, metals 2.70% (manganese) to 71.52% (iron) according to each metal and COD removal of 72.80%

Characterization of Carbon Molecular Sieve Membranes Supported on Ceramic Tubes

Carbon molecular sieve membranes have been analyzed in supported and unsupported configurations in this experimental study. The membranes were used to adsorb CO2, N2 and CH4, and their adsorption data were analyzed to establish differences in rate and capacity of adsorption between the two types of samples (supported and unsupported). Experimental results show an important effect of the support, which can be considered as an additional parameter to tailor pore size on these carbon membranes. Immersion calorimetry values were measured by immersing the membranes into liquids of different molecular dimensions (dichloromethane, benzene, n-hexane, 2,2-dimethylbutane). Similarities were found between adsorption and calorimetric analysis. The pore volume of the samples analyzed ranged from 0.016 to 0.263 cm3/g. The effect of the pyrolysis temperature, either 550 or 700 °C, under N2 atmosphere was also analyzed. Quantification of the pore-size distribution of the support was done by liquid-liquid displacement porosimetry. The composite membrane was used for CO2/CH4 separation before and after pore plugging was done. The ideal selectivity factors value (4.47) was over the Knudsen theoretical factor (0.60) for membrane pyrolyzed at 600 °C, which indicates the potential application of these membranes for the separation of low-molecular weight gases.

Ba0.5Sr0.5Co0.8Fe0.2O3-delta ceramic hollow-fiber membranes for oxygen permeation

Setf-supported asymmetric hollow-fiber membranes of mixed oxygen-ionic and electronic conducting perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) were prepared by a combined phase-inversion and sintering technique. The starting inorganic powder was synthesized by combined EDTA-citrate complexing process followed by thermal treatment at 600 degrees C. The powder was dispersed in a polymer solution and then extruded into hollow-fiber precursors through a spinneret. ne fiber precursors were sintered at elevated temperatures to form gastight membranes, which were characterized by SEM and gas permeation tests. Performance of the hollow fibers in air separation was both experimentally and theoretically studied at various conditions. The results reveal that the oxygen permeation process was controlled by the slow oxygen surface exchange kinetics under the investigated conditions. The porous inner surface of the prepared perovskite hollow-fiber membranes considerably favored the oxygen permeation. The maximum oxygen flux measured was 0.031 mol-m(-2).s(-1) at 950 degrees C with the sweep gas flow rate of 0.522 mol(.)m(-2).s(-1). To improve the oxygen flux of BSCF perovskite membranes, future work should be focused on surface modification rather than reduction of the membrane thickness. (c) 2006 American Institute of Chemical Engineers.

Adherent Nanoporous Anatase TiO2 Membranes on Stainless Steel Substrates

Nanostructured TiO2 is one of the most commonly used materials in photocatalytic applications and photochemical solar cells. This article describes a method to synthesize nanoporous anatase TiO2 membranes directly on stainless steel (SS), an easily available substrate by anodization to form amorphous TiO2 and a subsequent heat treatment to convert it into anatase, the photoactive phase. To obtain adherent membranes with interfaces that are resistant to peeling, both anodization and heat treatment parameters need to be optimized to obtain a heterostructure that contains a Ti film between the TiO2 membrane and the substrate.

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.

Structural characterization, stability and electrical properties of strontium niobate ceramic

The double perovskite oxide Sr2CrNbO6 has a cubic structure according to powder X-ray diffraction. After reducing in CO, Sr2CrNbO6 still exhibited a cubic structure refined by Rietveld technique. The TG analysis indicated that Sr2CrNbO6 loses 0.127 oxygen per formula unit from 400 to 700 degrees C in H-2. The morphology and compositions of this ceramic did not significantly change on reduction

Preparation and characterization of palladium-based composite membranes by electroless plating and magnetron sputtering

Pd and Pd-Ag (24 wt.%) alloy composite membrane were prepared by electroless plating and magnetron sputtering, respectively. The membranes were characterized by scanning electron microscopy (SEM) and H-2 permeation measurement. Commercial microfiltration ceramic membrane were coated with gamma-Al2O3-based layer by the sol-gel method and used as substrate of Pd and Pd-Ag alloy film. Both the as-prepared membranes were shown: to be He gas-tight at room temperature with a thickness of <1 mu m. Permeation results showed that H-2 permeation through these composite membranes is mainly dominated by the surface chemistry of H-2 on or/and in the membranes. The membranes exhibited a high permeation rate of H-2 and a H-2/N-2 permselectivity of higher than 60 in the optimized operation conditions. (C) 2000 Elsevier Science B.V. All rights reserved.

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.

Hydrogen-permeation characteristics of a SrCeO3-based ceramic separation membrane:Thermal, ageing and surface-modification effects

Dense ceramics with mixed protonic-electronic conductivity are of considerable interest for the separation and purification of hydrogen and as electrochemical reactors. In this work, the hydrogen permeability of a Sr_0.97Ce_0.9Yb_0.1O_{3 - δ} (SCYb) membrane with a porous Pt catalytic layer on the hydrogen feed-exposed side has been studied over the temperature range 500-804 °C employing Ar as the permeate sweep gas. A SiO₂-B₂O₃-BaO-MgO-ZnO-based glass-ceramic sealant was successfully employed to seal the membrane to the dual-chamber reactor. After 14 h of exposure to 10% H₂:90% N₂ at 804 °C, the H₂ flux reached a maximum of 33 nmol cm^{- 2} s^{- 1}, over an order of magnitude higher than that obtained on membranes of similar thickness without surface modification. The permeation rate then decreased slowly and moderately on annealing at 804 °C over a further 130 h. Thereafter, the flux was both reproducible and stable on thermal cycling in the range 600-804 °C. The results indicate an important role of superficial activation processes in the flux rate and suggest that hydrogen fluxes can be further optimised in cerate-based perovskites. © 2009 Elsevier B.V. All rights reserved.