Oxygen Permeation Rate Research Articles

Ba effect in doped Sr(Co0.8Fe0.2)O3-δ on the phase structure and oxygen permeation properties of the dense ceramic membranes

BaxSr1-xCo0.8Fe0.2O3-δ (x=0∼1.0) composite oxides were prepared by a combined EDTA and citrate complexing method. The doping effect of Ba on the phase structure, phase stability and oxygen permeation properties of the mixed conductors was investigated with combined XRD, H2-TPR, O2-TPD techniques and oxygen permeation studies. It was found that the perovskite structure was sustained in the whole range of the oxygen activity investigated (0.21∼10−6 atm) when 0.3≤x≤0.5. But for the materials with a differed doping content of Ba (x=0∼0.1, 0.7∼1.0), a phase transition was accompanied which was deleterious to the integrality of the membrane during operation. The relationship of phase structure and stability with tolerance factor was proposed. The doping of Ba in Sr(Co0.8Fe0.2)O3−δ could not lead to the improvement of these materials in the resisting of reduction, but the synergetic effect between cobalt and iron in the material was improved. Considerable high oxygen permeation rates were found for the BSCFO membranes in the whole range of Ba doping content. The Ba0.3Sr0.7Co0.8Fe0.2O3−δ membrane had the highest oxygen permeation flux, (1.19 ml/cm2 min for 1.50 mm thickness membrane at 850°C), the lowest activation energy for oxygen transportation (37.8 KJ/mol at the temperature range of 731°C∼950°C), and the lowest critical temperature for the change in the activation energy (731°C).

Synthesis, oxygen permeation study and membrane performance of a Ba0.5Sr0.5Co0.8Fe0.2O3−δ oxygen-permeable dense ceramic reactor for partial oxidation of methane to syngas

Abstract Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCFO) oxide was synthesized by a combined EDTA–citrate complexing method. The partial substitution of Sr in SrCo0.8Fe0.2O3−δ by Ba led to obvious improvement in the phase stability of the material at high temperatures. Under an air/helium oxygen gradient, the oxygen permeation fluxes of BSCFO were considerably high, a permeation flux ≈1.6 ml/cm2 min was achieved for a 1.5 mm membrane at 950°C, when P′O2=0.21 atm and P″O2=0.05 atm. The oxygen permeation was rate-determined mainly by oxygen bulk diffusion under non-reducing environment within the membrane thickness (1.5–1.8 mm) and temperature range (800–900°C) investigated. The oxygen permeation flux kept at 1.1–1.2 ml/cm2 min under ambient air/helium oxygen gradient during more than 1000 h operation. However, at lower temperatures, the permeation flux slowly decreased in an exponential relationship with time, which was possibly due to the phase decomposition of the material. Two membrane configurations and three cases were investigated for the partial oxidation of methane to syngas in a planar BSCFO reactor with LiLaNiOx/γ-Al2O3 as the reforming catalyst. The decrease in the distance between membrane surface and the reforming catalyst led to increase in the oxygen permeation fluxes and the role of surface exchange at the reaction membrane side in the oxygen permeation rate determination. High temperature treatment made some catalyst deposit onto the membrane surface, which led to a change of the oxygen exchange mechanism at the reaction side membrane surface, and resulted in an increase in oxygen permeation flux and decrease in activation energy of oxygen surface exchange. The stable long-term performance of the membrane reactor demonstrated that the permeation was still controlled by surface oxygen exchange of the reaction side membrane surface after the high temperature treatment. At 875°C, a permeation flux of 11.5 ml/cm2 min, methane conversion of 97–98%, and CO selectivity of 95–97% were achieved.

Ceramic membrane reactor for synthesis gas production

AbstractMembrane reactors enable synthesis‐gas production from methane and air while avoiding the need for separation of the nitrogen either before or after the reaction. A stable membrane was developed by spray deposition of a dense thin film of La0.5Sr0.5Fe0.8Ga0.2O3 − δ on a high‐purity porous α‐alumina tube. The oxygen permeation rate at 850°C was 2.5 × 10−7 mol·cm−2·s−1. A quartz tube was placed coaxially around the membrane and the shell filled with a rhodium catalyst. Air was fed to the tube and methane to the shell. At 850°C the methane conversion was 97% and the selectivity to carbon monoxide approached 100%. Rapid radial mixing of the oxygen in the shell is essential to prevent coking and undesirable reactions. The membrane decomposes at 780°C in pure CH4, but remains stable up to 970°C in a mixture of 90‐mol % CH4 and 10‐mol % CO2.

Investigation on POM reaction in a new perovskite membrane reactor

A perovskite-type oxide of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCFO) shows mixed (electronic/oxygen ionic) conductivity at high temperatures. Membrane made of the oxide has high oxygen permeability under air/helium oxygen partial pressure gradient. At 850°C, oxygen permeation rate maintained about 1.15 ml/cm 2 min for more than 1000 h under ambient air/helium oxygen gradient. A membrane reactor constructed from the oxide membrane was applied for the partial oxidation of methane (POM) to syngas, LiLaNiO x /γ-Al 2O 3 with 10 wt.% Ni loading was used as the packed catalyst. At the initial stage, oxygen permeation rate, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation rate to reach its steady state. A membrane reactor made of BSCFO was successfully operated for POM reaction at 875°C for about 500 h without failure, with methane conversion of >97%, CO selectivity of >95% and oxygen permeation rate of about 11.5 ml/cm 2 min. Under membrane reaction condition, the POM reaction mechanism was suggested to obey the CRR (complete combustion of CH 4 to CO 2 and H 2O and a subsequent reforming reaction of the residual CH 4 and with CO 2 and H 2O to CO and H 2) mechanism.

Investigations towards the use of Gd 0.7Ca 0.3CoO x as membrane in an exhaust gas sensor for NO x

Application of a material with the nominal composition Gd 0.7Ca 0.3CoO x is considered for use as membrane material in an exhaust gas sensor for NO x . SEM–EDX and XRD measurements revealed that after sintering at 1200°C in air, three co-existing phases are present: (Gd 0.6Ca 0.4) 2CoO x (60 vol.%), GdCoO 3 (26 vol.%) and CoO. Catalytic activities were investigated using temperature-programmed reaction (TPR). Whereas the composite Gd 0.7Ca 0.3CoO x shows no catalytic activity towards NO x reduction, as required in the targeted application, the single phase components (Gd 0.6Ca 0.4) 2CoO x and GdCoO 3, were found both to be active. The permeation rates exhibited by the composite material, at 1000°C, are considered too low for real application of this material. Oxygen permeation rates through perovskite-structured GdCoO 3− δ and (Gd 0.6Ca 0.4) 2CoO 4− δ , having the K 2NiF 4-structure, were found to be below the range of detection (<10 −11 mol/cm 2 s).

Mixed electronic–oxide ionic conductivity and oxygen permeating property of Fe-, Co- or Ni-doped LaGaO 3 perovskite oxide

Mixed electronic–oxide ionic conductivity in LaGaO 3-based oxide doped with Fe, Co or Ni was investigated in this study. The electric conductivity was greatly increased by doping Fe, Co, or Ni for the Ga site of La 0.8Sr 0.2GaO 3. Compared to the conventional mixed electronic–ionic conductors such as LaCoO 3, these LaGaO 3-based oxides exhibited a lower electronic conductivity but a higher oxide ion conductivity. In particular, Fe-doped LaGaO 3 exhibited a high oxygen permeation rate and a stability against reduction. Consequently, higher CH 4 conversion in the partial oxidation of CH 4 was attained by using La 0.8Sr 0.2Ga 0.6Fe 0.4O 3 in the place of the conventional candidate material of La 0.6Sr 0.4Fe 0.8Co 0.2O 3 for the oxygen permeation membrane. As a result, this study revealed that LaGaO 3-based oxide doped with Fe, Co or Ni for Ga site is a new family of mixed electronic–oxide ionic conductors.

Role of Perovskite Phase on the Oxygen Permeation Properties of the Sr4Fe6 − xCox O 13 + δ System

Oxygen permeation measurements of the system with 0 ≤ ≤ 2.0 are presented. samples prepared by solid‐state method consist of single‐phase for 0 ≤ < 1.5 and a three‐phase mixture composed of the intergrowth phase with < 1.5, the perovskite phase , and the spinel phase for 1.5 ≤ ≤ 2.0. On the other hand, samples prepared by a sol‐gel method consist of single‐phase for the entire 0 ≤ ≤ 2.0. The composition consisting of the three‐phase mixture exhibits oxygen permeation fluxes one order of magnitude higher than the single‐phase . The higher oxygen permeation rate of the sample consisting of three phases is due to the perovskite phase since single‐phase perovskite permeates oxygen two orders of magnitude higher than the single‐phase . While the single‐phase samples show stable oxygen permeation rates as a function of time, the samples consisting of the three‐phase mixture show a decrease in oxygen permeation with time. © 2000 The Electrochemical Society. All rights reserved.

Partial oxidation of methane to syngas in a mixed-conducting oxygen permeable membrane reactor

Mixed-conducting oxygen permeable membranes represent a class of novel ceramic membranes, which exhibit mixed oxygen ionic and electronic conductivities. At high temperatures, oxygen can permeate through the membrane from the high to low oxygen pressure side under an oxygen concentration gradient. Theoretically, the permselectivity of oxygen is 100%. Recently, a novel mixed-conducting membrane—Ba0.5Sr0.5Co0.8Fe0.2O3−δ has been developed, which shows extremely high oxygen permeability and promising stability. Furthermore, the reactor made with such membranes was successfully applied to the partial oxidation of methane to syngas reaction using air as the oxygen source, which realized the coupling of the separation of oxygen from air and the partial oxidation of membrane reaction in one process. At 850°C, methane conversion > 88%, CO selectivity > 97% and oxygen permeation rate of about 7.8 mL/(cm2 · min) were obtained.

Preparation of oxygen gas barrier polypropylene films by deposition of SiOx films plasma-polymerized from mixture of tetramethoxysilane and oxygen

Silicon oxide (SiOx) film deposition on the surface of oriented poly(propylene) (OPP) films was done to form a new oxygen gas barrier material using plasma polymerization of the tetramethoxysilane (TMOS)/O2 mixture. The SiOx film deposition on OPP films never improved oxygen gas barrier properties. The inefficacy of the SiOx deposition was due to poor adhesion at the interface between the deposited SiOx and OPP films and also to the formation of cracks in the deposited SiOx film. If prior to the SiOx film deposition surface modification of OPP films was done by a combination of the argon plasma treatment and TMOS coupling treatment, this contributed effectively to strong adhesion leading to success in the SiOx deposition on the OPP film surface, and then the oxygen gas barrier ability was improved. The oxygen permeation rate through the SiOx-deposited OPP film was decreased from 2230 to 37–52 cm3/m2/day/atm, which was comparable to that of poly(vinylidene chloride), 55 cm3/m2/day/atm at a film thickness of 11 μm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2389–2397, 2000

Mixed Electronic-Oxide Ionic Conductivity and Oxygen Permeating Property in Ni Doped LaGaO3 Perovskite Oxide

Abstract It was found that LaGaO3 perovskite oxide doped with Ni for Ga site exhibits a high mixed electronic-oxide ionic conduction. Oxygen permeation rate was increased with increasing Ni content and it attained to a maximum value of 2.15 cm3/min cm2 at 1273 K when 25 mol% Ni was doped.

Model development for O 2 and N 2 permeation rates through CZ-resin vials

The headspace of vials containing oxygen-sensitive formulations is filled with a nitrogen blanket. This paper presents the development of a mathematical model to predict the oxygen and nitrogen permeation rates through the walls of plastic CZ-resin vials. The model estimates the time required for a nitrogen-filled vial to reach ambient nitrogen and oxygen levels. The permeation of oxygen and nitrogen through the vial is governed by Fick’s law and may be described by an exponential equation. Using the values for oxygen and nitrogen permeation through CZ-resin vial, the half-lives for the decrease in nitrogen level and increase in oxygen level was found to be 150 days and 15 days, respectively. This result can be attributed to the greater permeability of CZ-resin vial to oxygen (79.06 cm 3-mm/m 2-24 h-atm) when compared with nitrogen (12 cm 3-mm/m 2-24 h-atm). The ingress of oxygen into CZ-resin vials was determined experimentally and it was found to verify the model. These results indicate that CZ-resin vials may be inappropriate for packaging oxygen-sensitive formulations even in the presence of a nitrogen-filled headspace.

Oxygen Permeability and Phase Transformation of Sr0.9Ca0.1CoO2.5 + δ

Oxygen permeation properties of (A′=Ca, Sr, Ba, and Mg) were investigated. The oxides with ≤ 0.2 had hexagonal structure at room temperature. The disk membranes (1.0 mm thick) made of these oxides, when cooled from high temperature, showed significant rates of oxygen permeation down to critical temperatures characteristic of the kind of oxides, below which the rates sharply diminished. Among the oxides tested, showed the largest rate ( at standard temperature and pressure ) at 900°C. As indicated by the X‐ray diffraction and thermogravimetry‐differential thermal analysis, this oxide underwent phase transformation between the above structure (low‐temperature phase) and a cubic perovskite structure (high‐temperature phase), which were oxygen nonpermeable and oxygen permeable, respectively. On heating, the oxygen content (2.5 +δ) of the oxide decreased in two steps, i.e., first from 2.75 to 2.6 over the temperature range 400 to 600°C without changing the structure, and then from 2.6 to 2.5 at the temperature of transformation to the high‐temperature phase (about 900°C). The rate of oxygen permeation of the oxide at 900°C was found to depend on the membrane thickness. Based on these results, oxygen permeation and its relevance to phase transformation are discussed. © 1999 The Electrochemical Society. All rights reserved.

99/02602 A novel process to fabricate membrane electrode assemblies for proton exchange membrane fuel cells

Lithium microbatteries with different positive electrode materials (V2O5, LiCoO2, TiOS) in association with a solid electrolyte (LiPONB) and a lithium negative electrode are very promising energy storage systems that can fit all the applications requirements. One of the challenges of the technology is related to the fact that lithium microbatteries are easily degraded in atmosphere. Indeed, these devices require encapsulation with a barrier material, which exhibits extremely low permeation rates for water vapour and oxygen. To obtain such a high barrier, we chose to direct our studies on layers deposited by plasma-enhanced chemical vapour deposition (PECVD), and more particularly on amorphous materials like silicon oxide (SiOx) and silicon nitride (SiNx). Both the active layers of the microbattery architecture and the multilayer encapsulation stack will be discussed.

Oxygen permeation rates through ion-conducting perovskite membranes

An explicit oxygen permeation model has been developed for ion-conducting membranes with a high ratio of electronic to ionic conductivity, which makes it possible to correlate the permeation flux to directly measurable variables. Surface exchange kinetics at each side of the membrane is emphasized and their resistance to oxygen permeation has been quantitatively distinguished from the bulk diffusion resistance. A series of experimental measurements of oxygen fluxes for La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ over a wide range of temperature and oxygen partial pressures were used for model regression purposes and for mechanism analysis. It is concluded that oxygen permeation at low temperatures (750°C) is limited by the rate of oxygen-ion recombination but is dominantly controlled by bulk diffusion at high temperatures (950°C). This is consistent with activation energies for oxygen vacancy diffusion and for the surface exchange rates, which are estimated at 74 kJ/mol and 227, 241 kJ/mol, respectively.

Comparative effects of de-aeration and package permeability on ascorbic acid loss in refrigerated orange juice

Several factors including pH, cultivar, extraction method, metal ion content and storage conditions affect the rate of ascorbic acid loss in refrigerated fruit juices. While oxygen permeation rate and product de-aeration also influence ascorbic acid loss, little comparative data on these two variables exist despite the potential usefulness of such data in optimizing the packaging of juice. De-aerated and non-de-aerated single-strength orange juices were packaged and stored at 7°C in experimental glass containers constructed with oxygen permeability rates of 0·35, 0·39, 0·43, 0·79, 1·18 and 1·60 ml/day/container at 7°C. The rate of ascorbic acid degradation inversely correlated with permeation rate for both de-aerated and non-de-aerated juices regardless of initial dissolved oxygen content. Degradation was best described by zero-order and first-order kinetics for de-aerated and non-de-aerated juices, respectively. Headspace volume had no effect on ascorbic acid loss in both de-aerated and non-de-aerated juices when nitrogen flushed. Juice in high oxygen permeability containers showed a faster decrease in ascorbic acid content, independent of initial dissolved oxygen content. These results indicate that both package barrier properties and de-aeration are major factors in maintaining ascorbic acid in refrigerated orange juice. Copyright © 1999 John Wiley & Sons, Ltd.

Preparation of oxygen gas barrier poly(ethylene terephthalate) films by deposition of silicon oxide films plasma‐polymerized from a mixture of tetramethoxysilane and oxygen

To prepare silicon oxide (SiOx)-deposited poly(ethylene terephthalate) films with high oxygen gas barrier capability, SiOx deposition by plasma polymerization has been investigated from the viewpoint of chemical composition. Tetramethoxysilane (TMOS) is suitable as a starting material for the synthesis of the SiOx films. The SiOx deposition under self-bias, where the etching action occurs around an electrode surface, is effective in eliminating carbonaceous compounds from the deposited SiOx films. There is no difference in the chemical composition between the SiOx films deposited under self-bias and under no self-bias. The SiOx films are composed of a main component of SiOSi networks and a minor component of carbonized carbons. The SiOx films deposited under no self-bias from the TMOS/O2 mixture show good oxygen gas barrier capability, but the SiOx films deposited under the self-bias show poor capability. The minimum oxygen permeation rate for poly(ethylene terephthalate) films deposited SiOx film is 0.10 cm3 m−2 day−1 atm−1, which corresponds to an oxygen permeability coefficient of 1.4 × 10−17 cm3-cm cm−2 s−1 cm−1 Hg for the SiOx film itself. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2091–2100, 1999

Preparation of oxygen gas barrier poly(ethylene terephthalate) films by deposition of silicon oxide films plasma-polymerized from a mixture of tetramethoxysilane and oxygen

To prepare silicon oxide (SiOx)-deposited poly(ethylene terephthalate) films with high oxygen gas barrier capability, SiOx deposition by plasma polymerization has been investigated from the viewpoint of chemical composition. Tetramethoxysilane (TMOS) is suitable as a starting material for the synthesis of the SiOx films. The SiOx deposition under self-bias, where the etching action occurs around an electrode surface, is effective in eliminating carbonaceous compounds from the deposited SiOx films. There is no difference in the chemical composition between the SiOx films deposited under self-bias and under no self-bias. The SiOx films are composed of a main component of SiOSi networks and a minor component of carbonized carbons. The SiOx films deposited under no self-bias from the TMOS/O2 mixture show good oxygen gas barrier capability, but the SiOx films deposited under the self-bias show poor capability. The minimum oxygen permeation rate for poly(ethylene terephthalate) films deposited SiOx film is 0.10 cm3 m−2 day−1 atm−1, which corresponds to an oxygen permeability coefficient of 1.4 × 10−17 cm3-cm cm−2 s−1 cm−1 Hg for the SiOx film itself. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2091–2100, 1999

Effect of Surface Modification on Catalytic Properties of Sr[sub 0.25]Bi[sub 0.5]FeO[sub 3−δ] Membranes

Membranes of mixed ionic-electronic conductors have been widely studied for gas separation, electrosynthesis, and removal of pollutants. Not only the rates but also the selectivities of these processes are determined critically by the surface catalytic properties of the membranes, which in turn are determined by the morphology, microstructure, and composition of the surfaces. In this study, nanoporous Sr0.25Bi0.5FeO3-δ (SBF) layers, with or without the impregnation of catalysts, were applied to dense SBF membranes using a sol-gel process to investigate the effect of surface modification on the catalytic properties. It is found that both oxygen permeation rates and methane conversion of a dense SBF mixed-conducting membrane coated with a nanoporous SBF layer are much higher than those of an as-sintered SBF membrane without surface modification. Nanoparticles of nickel loaded into the porous SBF surface layer further enhanced methane conversion.

Oxygen Permeation Through Composite Oxide-Ion and Electronic Conductors

Oxygen Permeation Through Composite Oxide-Ion and Electronic Conductors

Effect of crosslinking on the physicochemical properties of proton conducting PVDF-g-PSSA membranes

Poly(vinylidene fluoride) (PVDF) membranes, radiation-grafted with styrene and sulfonated, were studied as a candidate material for polymer electrolyte fuel cell (PEFC). In particular the effect of the use of crosslinkers in the polymer structure was investigated using bis(vinyl phenyl)ethane (BVPE) and divinylbenzene (DVB) as reagents. Water uptake in the H+ form, proton conductivity and ion exchange capacity of the PVDF-g-PSSA membranes, as well as transport properties of oxygen and hydrogen were determined at room temperature. Crosslinking with DVB resulted in a more pronounced decrease in the properties; the use of BVPE had no significant influence. Even on the permeation of oxygen and hydrogen the BVPE had little effect: the diffusion coefficient and solubility remained at the same level as for the non-crosslinked membranes. Increasing the membrane thickness was found to be at least as effective in reducing the oxygen permeation rate as using crosslinkers.