Oxygen Permeation Rate Research Articles

Solvent impact on esterification and film formation ability of nanofibrillated cellulose

In this study we have manufactured nanofibrillar cellulose and modified the fibre surface with ester groups in order to hydrophobise the surface. Nanofibrillated cellulose was chosen to demonstrate the phenomena, since due to its high surface area the effects at issue are pronounced. The prepared NFC ester derivatives were butyrate, hexanoate, benzoate, naphtoate, diphenyl acetate, stearate and palmitate. X-ray photoelectron spectroscopy, solid state NMR and contact angle measurements were used to demonstrate the chemical changes taking place on the cellulose surface. NFC ester derivatives can be prepared after a careful solvent exchange to a water-free solvent medium has been carried out. Butyl and palmitoyl esters were chosen for film forming tests due to the difference in their carbon chain lengths, and their contact angles and water vapour and oxygen permeation rates were studied. The prepared nanocellulose esters show increased hydrophobicity even at very low levels of substitution and readily form films when the films are prepared from acetone dispersions. The permeation rates suggest a potential use as barrier materials.

Modeling of a combined ion transport and porous membrane reactor for oxy-combustion

Ion transport membranes (ITMs) offer promising technology for high purity oxygen production (up to 99%) without adversely affecting the efficiency of the oxy-fired plants. The permeation rate of such ITMs can be increased by replacing the conventional inert sweep gas with a reactant/diluent mixture (e.g. CO2, CH4) as this reduces the permeate partial pressure on the permeate side of the membrane, which, along with the temperature, governs the permeation flux. The significant limitation of this approach is that an uncontrolled, exothermic consumption of the permeated specie, can lead to membrane damage, and thus limits the potential of ITMs using reactive sweep gases (i.e. ITM reactors). By using a multichannel ITM reactor (isothermal reactor), it is proposed to operate the ITM reactor at, or near to isothermal conditions (i.e. a spatially uniform temperature). This may be achieved by introducing a reactant into the permeate stream uniformly across the entire ITM reactor length from an adjacent channel with porous walls. The present work is aimed at modeling a nearly isothermal reactor using an ITM and a porous membrane to achieve uniform stoichiometric ratio of fuel/O2 in order to have a uniform combustion all along the length of the membrane. A two-dimensional, computational fluid dynamics (CFD) model is solved to study the characteristics. The simulations are based on the numerical solution of the conservation of mass, momentum, energy and species transport equations of two dimensional flows. For the CFD calculations, the commercial solver FLUENT has been used. The models used have been validated against the experimental results found in the literature and are found to be in good agreement. The influence on the performance of oxygen separation through the ITM has been studied by varying the flow conditions at the permeate side. Results show that an approximate uniform combustion can be achieved along with effective thermal management of the ITM using the present isothermal reactor. It is also observed that for a constant mass flow rate of fuel mixture, the permeation rate of oxygen through ITM increases with the increase in CH4/CO2 ratio. The results indicate that the oxygen permeation flux increases by approximately 3 times for reactive case compared to separation only case. Moreover it is shown that using the present reactor model the reaction zone can be controlled.

La–Sr–Fe–Co oxygen transport membranes on metal supports deposited by low pressure plasma spraying-physical vapour deposition

Dense La0.6Sr0.4Fe0.8Co0.2O3−δ (LSFC) membranes were successfully prepared on NiCoCrAlY metal supports by low pressure plasma spraying-physical vapour deposition. He leakage rate tests and microstructural analysis by SEM of the as-deposited films showed that a gas-tight membrane layer is achieved. Membrane thicknesses are between 40 and 65µm. The oxygen permeation flux was determined at atmospheric pressure in an air-Ar gradient at different temperatures between 700 and 950°C and compared with 1mm thick LSFC pellet. Although leakage was detected, noteworthy oxygen permeation rate of the supported membranes (∼0.3mlcm−2min−1 at 885°C) is reported.

Electrochemical Measurement of the Oxygen Permeation Rate through Polymer Electrolyte Membranes

An electrochemical method is developed for the measurement of the oxygen permeation rate through perfluorosulfonic acid (PFSA) membranes at various temperatures and relative humidities (RH) using a fuel cell setup. The oxygen permeability is determined from the oxygen-crossover-rate limited oxygen reduction reaction (ORR) current. The current vs. applied voltage relationship during the oxygen permeation rate measurement can be fully explained by a kinetic model accounting for the anode and cathode reactions, oxygen transport through the membrane, and oxygen diffusion from the cathode electrode to cathode flow channel. While demonstrated for a PFSA membrane, the presented electrochemical method to quantify the oxygen permeability is also applicable to any other types of proton or hydroxide conducting ionomeric membranes.

Laminar oxy-fuel diffusion flame supported by an oxygen-permeable-ion-transport membrane

A numerical model with detailed gas-phase chemistry and transport was used to predict homogeneous fuel conversion processes and to capture the important features (e.g., the location, temperature, thickness and structure of a flame) of laminar oxy-fuel diffusion flames stabilized on the sweep side of an oxygen permeable ion transport membrane (ITM). We assume that the membrane surface is not catalytic to hydrocarbon or syngas oxidation. It has been demonstrated that an ITM can be used for hydrocarbon conversion with enhanced reaction selectivity such as oxy-fuel combustion for carbon capture technologies and syngas production. Within an ITM unit, the oxidizer flow rate, i.e., the oxygen permeation flux, is not a pre-determined quantity, since it depends on the oxygen partial pressures on the feed and sweep sides and the membrane temperature. Instead, it is influenced by the oxidation reactions that are also dependent on the oxygen permeation rate, the initial conditions of the sweep gas, i.e., the fuel concentration, flow rate and temperature, and the diluent. In oxy-fuel combustion applications, the sweep side is fuel-diluted with CO2, and the entire unit is preheated to achieve a high oxygen permeation flux. This study focuses on the flame structure under these conditions and specifically on the chemical effect of CO2 dilution. Results show that, when the fuel diluent is CO2, a diffusion flame with a lower temperature and a larger thickness is established in the vicinity of the membrane, in comparison with the case in which N2 is used as a diluent. Enhanced OH-driven reactions and suppressed H radical chemistry result in the formation of products with larger CO and H2O and smaller H2 concentrations. Moreover, radical concentrations are reduced due to the high CO2 fraction in the sweep gas. CO2 dilution reduces CH3 formation and slows down the formation of soot precursors, C2H2 and C2H4. The flame location impacts the species diffusion and heat transfer from the reaction zone towards the membrane, which affects the oxygen permeation rate and the flame temperature.

Interactions between oxygen permeation and homogeneous-phase fuel conversion on the sweep side of an ion transport membrane

The interactions between oxygen permeation and homogeneous fuel oxidation reactions on the sweep side of an ion transport membrane (ITM) are examined using a comprehensive model, which couples the dependency of the oxygen permeation rate on the membrane surface conditions and detailed chemistry and transport in the vicinity of the membrane. We assume that the membrane surface is not catalytic to hydrocarbon or syngas oxidation. Results show that increasing the sweep gas inlet temperature and fuel concentration enhances oxygen permeation substantially. This is accomplished through promoting oxidation reactions (oxygen consumption) and the transport of the products and reaction heat towards the membrane, which lowers the oxygen concentration and increases the gas temperature near the membrane. Faster reactions at higher fuel concentration and higher inlet gas temperature support substantial fuel conversion and lead to a higher oxygen permeation flux without the contribution of surface catalytic activity. Beyond a certain maximum in the fuel concentration, extensive heat loss to the membrane (and feed side) reduces the oxidation kinetic rates and limits oxygen permeation as the reaction front reaches the membrane. The sweep gas flow rate and channel height have moderate impacts on oxygen permeation and fuel conversion due to the residence time requirements for the chemical reactions and the location of the reaction zone relative to the membrane surface.

Role of Ga3+ and Cu2+ in the High Interstitial Oxide-Ion Diffusivity of Pr2NiO4-Based Oxides: Design Concept of Interstitial Ion Conductors through the Higher-Valence d10 Dopant and Jahn–Teller Effect

We have investigated the crystal structure, nuclear- and electron-density distributions, electronic structure, and oxygen permeation rate of three K2NiF4-type oxides of Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ, Pr2Ni0.75Cu0.25O4+δ, and Sr2Ti0.9Co0.1O4–e, in order to study the role of d10 Ga3+, Jahn–Teller Cu2+, and interstitial oxygen O3 in the high oxygen diffusivity of Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ. The composition Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ has a larger amount of interstitial oxygen O3 atoms (δ = 0.31 at room temperature (RT)) compared with Pr2Ni0.75Cu0.25O4+δ (δ = 0.19 at RT) and the oxygen deficient Sr2Ti0.9Co0.1O4–e (e = 0.02 at RT). The interstitial O3 atom is stabilized by (1) the substitution of (Ni,Cu)2+ by higher valence Ga3+, (2) static atomic displacements of the apical O2 oxygen, and (3) local relaxation near d10 Ga3+. Nuclear-density distributions of Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ and Pr2Ni0.75Cu0.25O4+δ at high temperatures have visualized the −O2–O3–O2– diffusional pathway of oxide ions, w...

Partial oxidation of methane in Ba0.5Sr0.5Co0.8Fe0.1Ni0.1O3-δ ceramic membrane reactor

Ba0.5Sr0.5Co0.8Fe0.1Ni0.1O3-δ(BSCFNiO) perovskite oxides were synthesized using a combined EDTA-citrate complexation method, and then pressed into disk and applied in a membrane reactor. The performance of the BSCFNiO membrane reactor was studied for partial oxidation of methane over Ni/a-Al2O3 catalyst. The time dependence of oxygen permeation rate and catalytic performance of BSCFNiO membrane during the catalyst initiation stage were investigated at 850°C. In unsteady state, oxygen permeation rate, methane conversion and CO selectivity were closely related to the state of the catalyst. After 300 min from the initial time, the reaction condition reached to steady state and oxygen permeation rate were obtained about 11.7cm3·cm−2·min−1. Also, the performance of membrane reactor was studied at the temperatures between 750 and 950°C. The results demonstrated good performance for the membrane reactor, as CH4 conversion and CO selectivity permeation rate reached 98% and 97.5%, respectively, and oxygen permeation rate was about 14.5 cm3·cm−2·min−1 which was 6.8 times higher than that of air-helium gradient. Characterization of membrane surface by SEM after reaction showed that the original grains disappeared on both surfaces exposed to the air and reaction side, but XRD profile of the polished surface membrane indicated that the membrane bulk preserved the perovskite structure.

A novel ion transport membrane reactor for fundamental investigations of oxygen permeation and oxy-combustion under reactive flow conditions

Ion transport membrane (ITM) reactors present an attractive technology for combined air separation and fuel conversion in applications such as syngas production, oxidative coupling or oxy-combustion, with the promise of lower capital and operating costs, as well higher product selectivities than traditional technologies. The oxygen permeation rate through a given ITM is defined by the membrane temperature and oxygen chemical potential difference across it. Both of these parameters can be strongly influenced by thermochemical reactions occurring in the vicinity of the membrane, though in the literature they are often characterized in terms of the well mixed product stream at the reactor exit. This work presents the development of a novel ITM reactor for the fundamental investigation of the coupling between fuel conversion and oxygen permeation under well defined fluid dynamic and thermodynamic conditions, including provisions for spatially resolved, in-situ investigations. A planar, finite gap stagnation flow reactor with optical and probe access to the reaction zone is used to facilitate in-situ measurements and cross-validation with detailed numerical simulations. Using this novel reactor, baseline measurements are presented to elucidate the impact of the sweep gas fuel (CH4) fraction on the oxygen permeation and fuel conversion. In addition, the difference between well-mixed gas compositions measured at the reactor outlet and those measured in the vicinity of the membrane surface are discussed, demonstrating the unique utility of the reactor.

Partial oxidation of methane in a Zr0.84Y0.16O1.92–La0.8Sr0.2Cr0.5Fe0.5O3−δ hollow fiber membrane reactor targeting solid oxide fuel cell applications

A membrane reactor has been investigated to reform methane into fuel suitable for solid oxide fuel cells (SOFCs). An oxygen-permeable Zr.84Y0.16O1.92 (YSZ)–La0.8Sr0.2Cr0.5Fe0.5O3−δ (LSCF) hollow fiber membrane coated with Ru catalyst at the lumen side is used to construct the reactor. The reactor is tested at elevated temperatures with the shell and lumen sides of the hollow fiber exposed to the atmosphere air and methane, respectively. The reaction of methane with the permeated oxygen proceeds at a remarkably fast rate. Methane throughput conversion over 90% is attained at 950 °C at a high methane feed rate of 14.7 cm3 CH4 min−1 cm−2 membrane surface and oxygen permeation rate 7.9 cm3 min−1 cm−2; the effluent from the reactor is composed mainly of H2 (53.5%) and CO (35.7%), revealing that the dominating reaction occurring in the reactor is partial oxidation of the methane (POM). When the effluent is fed into a disk-shaped SOFC single cell, it exhibits stable performance. The mild exothermal nature of POM reaction and the high surface to volume ratio of hollow fiber membrane may allow us to construct and operate a compact autothermal methane reformer for SOFC applications.

La0.7Sr0.3FeO3−α perovskite hollow fiber membranes for oxygen permeation and methane conversion

Gas-tight La0.7Sr0.3FeO3−α (LSF) perovskite hollow fiber membranes were fabricated by the phase inversion/sintering technique using self-made ceramic powder. The permeation and reaction properties of the LSF membrane were investigated systematically by using He, CO2, H2 and CH4 as the sweep or reactive gas, respectively. The experimental results indicate that the cobalt-free LSF hollow fiber membrane exhibits good stability when exposed in inert gases like He and weak acid gases like CO2 but is not stable in a reducing environment. Continuous and severe segregation may occur when the LSF membrane is operated in H2 and CH4 atmosphere. The oxygen permeation rate is highly dependent on the formation rate of oxygen vacancies on the membrane sweeping side surface. Compared to He as the sweep gas, the use of CO2 restrained the oxygen permeation due to the strong chemical adsorption on the membrane surface. However, the LSF membrane still suffers from the reaction with H2 and CH4 to form porous debris on the membrane surface, which may initially promote the oxygen flux but will finally result in membrane leaking or even breakage. When using H2 or CH4 as the sweep gas, the oxygen in the air feed can be depleted completely by permeating through the membrane. Although the LSF membrane exhibits a kind of catalytic activity to the partial oxidation of methane into syngas with a maximum CO yield of 1.2%, additional catalyst is required to avoid the deep oxidation of the products so that high syngas yields can be achieved.

Effects of separation layer thickness on oxygen permeation and mechanical strength of DL-HFMR-ScSZ

It has been demonstrated in our previous studies that in order for greater methane conversion and less coke-formation, a higher oxygen permeation rate through the outer oxygen separation layer of a functional dual-layer ceramic hollow fibre membrane is needed. Besides new membrane materials with higher oxygen permeability, another way of improving oxygen permeation is to reduce the separation layer thickness, although this strategy is limited by the characteristic thickness, Lc, where bulk diffusion and surface oxygen exchange are both important. As a result, a series of La0.80Sr0.20MnO3−δ (LSM)-Scandia(10%)-Stabilized-Zirconia (ScSZ)/ScSZ-NiO functional dual-layer hollow fibres (DL-HF) with an outer oxygen separation layer thickness between approximately 8.0 and 72.4 μm were fabricated in this study, by using the single-step co-extrusion and co-sintering process. The effects of separation layer thickness on oxygen permeation and mechanical strength were investigated. The oxygen permeation of the LSM-ScSZ separation layer is more likely to be controlled by surface exchange at higher temperatures, and changes to mixed control by both bulk diffusion and surface exchange at lower temperatures. A thicker separation layer also results in a thinner catalytic substrate layer, and subsequently decreases the mechanical strength of the dual-layer hollow fibre membrane.

Effect of gas shutoff sequences on the degradation of proton exchange membrane fuel cells with dummy load during startup and shutdown cycles

In this paper, the effect of shutoff sequences of hydrogen and air on the degradation behaviours of proton exchange membrane fuel cells (PEMFCs) is investigated with two different shutdown procedures. After one of the gases is shut off, the dummy load is applied to consume the residual gas in the flow field. Theoretical analysis and experimental tests indicate that different gas shutoff sequences have great effect on the oxygen permeation rate across the membrane during introducing the dummy load, resulting in producing the H2/O2 interface at the anode in the next startup process. Electrochemical techniques, including the measurement of polarization curves, cyclic voltammetry, and cross-sectional scanning electron microscopy (SEM) of membrane electrode assemblies (MEAs) and transmission electron microscopy (TEM) of Pt/C catalyst are employed to evaluate the performance decay of PEMFCs after 1500 startup and shutdown cycles. The results show that the case if air is shut off firstly would significantly alleviate both the performance decay and the decrease in the electrochemically active surface area, resulting in an improvement in the durability of PEMFCs.

Designing polyethylene terephthalate‐based barrier resins

AbstractWe have studied the efficiencies of commercially available barrier resins used for food packaging and beverage bottle applications and compared them with resins made using copolymer and blending approaches. The effects of various copolymer related parameters that influence oxygen barrier performance and the underlying mechanisms for these effects in PET‐based copolymers and blends were investigated. Using these approaches, it is possible to make highly effective PET‐based copolymers for gas barrier applications. Blending of PET with phenolic and other organic materials shows equivalent barrier performance in PET copolymers having comonomer levels of <8‐mole %. Reduction in oxygen permeation rates results from the reduction or elimination of short range molecular motion of polyethylene terephthalate molecules. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

La0.2Sr0.8Fe0.8Ta0.2O3 − δ based thin film membranes with surface modification for oxygen production

High temperature dense ceramic membranes made from mixed ionic/electronic conducting perovskite ceramics represent a high potential as a reliable source for oxygen and syngas production. In this work, La0.2Sr0.8Fe0.8Ta0.2O3−δ based thin film perovskite system was evaluated, addressing the effect of structural surface modification on oxygen permeation rates. Membranes with ~20μm thick dense functional layer and varying surface area on permeate side were fabricated by a dip coating technique. Oxygen permeation was measured at temperatures between 800 and 1000°C by using varying partial pressure of O2 as a driving force. Maximum O2 flux values of ~5.8 and ~8.7ml·cm−2·min−1 were recorded for smooth and structured permeation surfaces, respectively. This indicates that the surface roughness, which corresponds to an increase in surface area at the permeate side; can lead to a significant improvement in oxygen permeation rates reaching ~50% at 1000°C.

MODELING AND OPTIMIZING PROPERTIES OF NANOCLAY–NITRILE RUBBER COMPOSITES USING BOX–BEHNKEN DESIGN

Abstract The mechanical behavior of acrylonitrile butadiene copolymer (NBR)–organomodified layered silicate (nanoclay) was modeled using design of experiments approach. A Box–Behnken design with three factors and three levels was used to model the relationship between properties of NBR nanocomposites and the ingredients. The factors considered in the design were silica content, nanoclay loading, and dicumyl peroxide content. The nanocomposites were evaluated for tensile strength, modulus, elongation at break, oxygen permeation rate, and effect of oil and heat aging on mechanical properties. Regression equations were generated to model the properties of interest and generate response surfaces and contour plots. The predicted properties of the nanocomposites were in good agreement with the experimental results. The contour plots were overlaid within the applied constraints to identify the combination of factor ranges that gives the optimal performance of the nanocomposites for application as control system bladders in satellite launch vehicles.

산소분리를 위한 Ba0.7Sr0.5CO0.8Fe0.2O3-δ관형 분리막 제조 및 투과 특성

<TEX>$Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$</TEX> 조성의 관형 분리막을 압출 성형 방법으로 제조하였다. 압출성형 직후 분리막의 TGA 분석결과 3단계의 무게감소로 첨가제와 탄산염이 분해되었고, 건조 수축율은 68 h 경과 후 변화가 없었으며 외경이 큰 분리막에서 높게 나타났다. 소결 후 분리막의 XRD 및 SEM 분석결과, 분리막은 단일상의 페롭스카이트 구조를 갖는 치밀한 막을 보였고, EDS 분석을 통해 <TEX>$Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$</TEX>와 유사한 성분함량을 가짐을 확인하였다. 두께 0.95 mm <TEX>$Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$</TEX> 관형 분리막의 압환강도(radial crushing strength)는 5.7 kgf/<TEX>$mm^2$</TEX>이였으며, <TEX>$950^{\circ}C$</TEX>에서 산소투과량은 146.85 mL/min(<TEX>$Jo_2$</TEX>=2.33 mL/<TEX>$min{\cdot}cm^2$</TEX>)를 나타냈었다. 투과 측의 진공펌프 사용이 쓸개 가스를 활용한 것보다 산소 투과량 증진에 효과가 있음을 알 수 있었다. Tubular <TEX>$Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-<TEX>${\delta}$</TEX>}$</TEX> membranes were prepared by extrusion. TGA results of green body membrane after extrusion showed three successive weight losses due to decomposition of organic additives and carbonate. Drying shrinkage rate of tubular <TEX>$Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-<TEX>${\delta}$</TEX>}$</TEX> membranes was no change after 68 h and higher in the membrane with large outer diameter. XRD and SEM results showed the sintered membranes were the single phase structure and dense. The stoichiometric molar ratio agreed well with composition ratio calculated by EDS results for <TEX>$Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-<TEX>${\delta}$</TEX>}$</TEX> membrane. Radial crushing strength of tubular <TEX>$Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-<TEX>${\delta}$</TEX>}$</TEX> membrane with 0.95 mm thickness was 5.7 kgf/<TEX>$mm^2$</TEX> and the oxygen permeation rate of same membrane was 146.85 mL/min (<TEX>$Jo_2$</TEX>=2.33 mL/<TEX>$min{\cdot}cm^2$</TEX>) at <TEX>$950^{\circ}C$</TEX>. Therefore, it was known that use of vacuum pump was more effective than that of sweep gas to obtain higher oxygen permeation flux.

Zr 0.84Y 0.16O 1.92–La 0.8Sr 0.2Cr 0.5Fe 0.5O 3− δ dual-phase composite hollow fiber membrane targeting chemical reactor applications

Gas-tight Zr 0.84Y 0.16O 1.92 (YSZ) and La 0.8Sr 0.2Cr 0.5Fe 0.5O 3− δ (LSCF) dual-phase composite hollow fibers were prepared by a phase-inversion/sintering technique. A high oxygen permeation rate of 3.8 ml cm −2 min −1 (STP), equivalent to 2.6 × 10 −6 mol cm −2 s −1, was measured with a 4.46-cm long hollow fiber by exposing its shell side to air and feeding CO at 30 ml/min into its lumen side at 950 °C. The CO oxidation reaction occurring in the as-constructed membrane reactor was found to proceed at a high rate and full conversion of CO to CO 2 was attained at the O 2 to CO ratio of 0.5. A numerical simulation was applied to the membrane reactor assuming plug flow model and equilibrium condition. The hollow fiber survived after 500 h of the test, and no significant change to its microstructure was observed. Since the YSZ–LSCF hollow fiber exhibited both high oxygen permeability and stability under stringent conditions, it holds promise for membrane reactor applications.

Mixed Conductivity, Nonstoichiometric Oxygen, and Oxygen Permeation Properties in Co-Doped Sr3Ti2O7−δ

Electrical conductivity and oxygen permeation rates in Co-doped Sr(3)Ti(2)O(7-δ) with Ruddesden-Popper type structures were investigated. The effects of metal dopants (M) in the Ti site of Sr(3)Ti(2)(M)O(7-δ) on the mixed conductivity were also studied. Doping of Sr(3)Ti(2)O(7-δ) with Co was found to be effective for improving the electrical conductivity as well as the oxygen permeation rate, which could be assigned to the increased oxygen vacancy concentration by doping Co(3+) into Ti(4+) sites. The nonstoichiometric oxygen of these oxides was measured by using a thermal gravimetric method. The creation of oxygen vacancies, which is compensated with Co(3+) doping, leads to higher oxide ion conductivity. The oxygen permeation rate monotonously increased with increasing amounts of Co in the Ti site. Sr(3)Ti(0.8)Co(1.2)O(7-δ) exhibited high oxide ion conductivity and a large oxygen permeation rate. The highest oxygen permeation rate achieved a value of 2.02 cc min(-1) cm(-2) at 1273 K for Sr(3)Ti(0.8)Co(1.2)O(7-δ). Neutron diffraction analysis and redox titration suggests that the oxygen diffusion occurs through oxygen vacancies in the perovskite block, but not through excess oxygen in the rock salt block.

Importance of pore structure control in porous substrate for high oxygen penetration in La 0.6Sr 0.4Ti 0.3Fe 0.7O 3 thin film for CH 4 partial oxidation

Effects of the pore structure of the support on the oxygen permeation rates of La 0.6Sr 0.4Ti 0.3Fe 0.7O 3 (LSTF) and La 0.7Sr 0.3Ga 0.6Fe 0.4O 3 (LSGF) films were investigated in this study. The pore structure of the support was an important factor for achieving a high oxygen permeation rate. Although LSGF membranes with the same thicknesses and compositions were used, the oxygen permeation rates increased with decreasing thickness of the substrate, suggesting a slow gas diffusion in substrate and so oxygen partial pressure on MIEC membrane may decrease comparing with that in gas phase. Oxygen permeation rates in LSGF membranes were also successfully simulated based on Fick's diffusion theory, and the model suggested that the gas diffusion in the porous substrate was highly important for achieving a high permeation rate in an asymmetric MIEC membrane. A laser manufacturing technique successfully prepared an LSTF substrate with straight pores, and the dense LSTF film with a 70 μm thickness was deposited on the prepared substrate. When the LSTF substrate with the straight pore structure was used for the LSTF film, the oxygen permeation rate was considerably improved and achieved a value as high as 15 cm 3/min cm 2 (three times higher than that for CH 4 fed to the substrate with random pores) under a CH 4 partial oxidation condition.