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Mixed ionic‐electronic conducting La0.8Ca0.2Fe0.95O3−δ‐Ag (LCF‐Ag) ceramic hollow fiber membranes possess high structural stability and up to 2.24‐fold higher oxygen permeation fluxes relative to LCF hollow fibers. In this work, the oxygen permeation of LCF‐Ag hollow fiber membrane module is simulated under sweep gas and vacuum operation modes, whereas the kinetic parameters were obtained by fitting the experimental data with the simplified Tan–Li model. The good correlation obtained from the data regression confirmed the compatibility of the selected model on the LCF‐Ag hollow fiber membrane. The simulated results revealed that the countercurrent flow configuration is generally favored in sweep gas operation given its potential of complete oxygen separation under optimized conditions. For vacuum operation, the oxygen yield is practically the same for both flow configurations at a moderate vacuum setting. At a very low vacuum pressure setting, however, cocurrent flow is preferred over countercurrent flow for maximizing the oxygen yield. [ABSTRACT FROM AUTHOR]

New CO2‐resistant dual‐phase Sm0.2Ce0.8O1.925–SrCo0.4Fe0.55Zr0.05O3‐δ (SDC‐SCFZ) ceramics present a promising outlook for potential future applications in membrane reactors and solid oxide fuel cells. Their high oxygen permeation flux and stability in CO2 sweep gas also allow their integration in oxyfuel combustion. Here the structural characteristics, electrical conductivities, thermal expansion behaviors, and oxygen permeabilities of four different SDC‐SCFZ membranes with weight ratios of 10:90, 25:75, 50:50, and 75:25 (SDC:SCFZ) are systematically studied. Among these four SDC‐SCFZ compositions, 0.6 mm‐thick 25 wt% SDC‐75 wt% SCFZ displayed the highest oxygen permeation fluxes that reach 1.26 mL min−1 cm−2 at 950°C and retained its phase integrity under alternating He and CO2 sweep gas over 72 hours of operation. This composite also showed a moderate thermal expansion coefficient of 1.90 × 10−5 K−1 between 30°C and 1000°C and an electrical conductivity of at least 16 S cm−1 at 550°C and above. Modeling studies revealed that the oxygen permeation fluxes through 25SDC‐75SCFZ are limited by surface exchange reactions from 700°C to 800°C and mixed bulk diffusion and surface exchange reactions above 800°C. [ABSTRACT FROM AUTHOR]

Ce0.85Sm0.15O1.925–Sm0.6Sr0.4Al0.3Fe0.7O3‐δ (SDC‐SSAF) hollow fiber membranes aimed for oxyfuel application are fabricated via a phase inversion‐sintering technique using powders synthesized from EDTA–citrate complex method. Oxygen ions transport is revealed to be the limiting step that determines the overall oxygen transport rate in SDC‐SSAF. SDC‐SSAF hollow fiber membrane attained a maximum flux of 2.6 ml min−1 cm−2 at 950°C under an oxygen partial pressure difference of 1/0.02 atm (feed/permeate). Variation in oxygen partial pressure on the permeate side exerts larger influence on the oxygen permeation flux relative to the change on the feed side. Stability tests over 100 h demonstrate stable oxygen permeation flux under both He and CO2 sweep conditions. [ABSTRACT FROM AUTHOR]

Oxygen permeable ceramic membranes have potential applications as the high temperature membrane reactors for cost-effective syngas production from methane partial oxidation. The prerequisite to realize this potential is that the membrane must be chemically stable at high temperatures in atmospheres containing reducing or acidic gases. To improve the stability of conventional perovskite (SrCo 0.8 Fe 0.2 O 3 − δ ) ceramic membranes, a doping strategy has been adopted. For this purpose, an asymmetric SrCo 0.8 Fe 0.1 Ga 0.1 O 3 − δ (SCFG) hollow fiber membrane has been fabricated. Its respective oxygen permeability is tested using helium, carbon dioxide, hydrogen and methane as sweep gases, which are the main gas components during the partial oxidation of methane (POM) to syngas. The oxygen permeability of the as-prepared SCFG hollow fiber membrane is up to 3.75 mL·min − 1 ·cm − 2 at 1000 °C when supplied with air as the feed and swept by He, while it declines to 1.85 mL·min − 1 ·cm − 2 when swept by CO 2 . Whereas, the oxygen permeation fluxes increase to 3.98 and 3.81 mL·min − 1 ·cm − 2 at 1000 °C, respectively, when the membrane is swept by the reducing gases such as 4% H 2 -96% He and 20% CH 4 -80% He, keeping a stable operation for 220 h. During the membrane reactor (an integrated separation-reaction process) performance for the POM reaction using the SCFG hollow fiber packed with Ni–Al 2 O 3 catalysts, the ratio of H 2 /CO, the CH 4 conversion, the selectivity of CO and the oxygen permeability are 2.08, 100%, 33%, and 4.14 ml min − 1 cm − 2 , respectively upon steady operation for 23 h at 800 °C. The promising stability of SCFG membranes during POM reactions has been attributed to the stabilizing effect provided by the doped gallium oxide, which acts as an anchor for the perovskite structure to maintain the integrity of the crystal lattice structure in the reducing atmosphere. [ABSTRACT FROM AUTHOR]

Oxygen selective ceramic membranes have many important applications, not only for air separation but also as membrane reactors for cost-effective chemical synthesis. However, the prerequisite to realize these potentials is their stability in the presence of acid gases of CO 2 and reducing atmosphere containing H 2 and CH 4 . This work seeks to validate the applicability of robust triple layer hollow fiber membranes consisting of (Ag+YSZ)/YSZ/La 0.8 Sr 0.2 MnO 3-δ (LSM)+YSZ to separate O 2 from air in the presence of these unavoidable gases for more advanced applications. To prepare the triple layer hollow fiber, the dual-layer fiber was firstly synthesized via a combined phase inversion and sintering method where the dense YSZ layer was present on top of the porous LSM-YSZ layer. We further deposited either porous Ag or its mixture with YSZ layer above the dense YSZ surface. The final fiber consists of three layers in sequence from outside surface to inside surface of Ag+YSZ/YSZ/LSM+YSZ. The dense central YSZ layer acts as the ionic conducting phase to prevent gas diffusion while the other two porous layers serve as the electronic conducting phase with catalytic effect to enhance the surface reaction kinetics. To overcome the electronic conductivity limitation of YSZ, silver (Ag) short circuit paste was additionally used to seal the membrane and electronically connect the outer and inner surfaces for electron shuttle for the two surface O 2 exchange reactions. Ag-YSZ coated fiber performed better than Ag coated fiber and showed increasing fluxes from 0.1 to 0.53 mL min −1 cm −2 upon increasing temperature from 700 to 900 °C. The O 2 fluxes remained constant irrespective of changing the sweep gas from pure He to its mixtures containing CO 2 , H 2 , or CH 4 ; mirroring the membrane robustness to tolerate these gases at high temperatures. [ABSTRACT FROM AUTHOR]

La 0.6 Ca 0.4 Co 0.2 Fe 0.8 O 3-δ (LCCF) ceramic powder prepared by sol-gel method was used to fabricate LCCF hollow fiber (HF) membranes via a combined phase inversion-sintering technique. Three types of LCCF HF membranes were developed by changing the composition of the internal coagulation bath containing H 2 O, EtOH or the mixture of NMP + EtOH. The best one was achieved via the mixture (0.7NMP + 0.3EtOH by weight). At 1000 °C, the oxygen flux reached 6.16 mL min−1 cm−2 under inert sweep gas; however, it reached 8.83 mL min−1 cm−2 when reactive CH 4 was used as the sweep gas, mirroring the high capability of oxygen transport through the membrane. The good stability of the developed LCCF membrane was confirmed by a series of long-term operation tests up to 300 h with sweep gas containing CO 2. The findings of this work can advance the applications of LCCF membranes to reactors where CO 2 atmosphere cannot be avoided. • LCCF oxygen permeable hollow fiber membranes were developed via a phase-inversion and sintering technology. • O 2 flux of LCCF-0.7NMP membrane was significantly improved compared to that of the LCCF-EtOH or LCCF-H 2 O membrane. • LCCF membrane exhibited excellent and stable O 2 permeation performance in CO 2 atmosphere. [ABSTRACT FROM AUTHOR]

[Display omitted] • A three-layer sandwich hollow fiber was prepared using one-step sintering. • Excellent membrane can hold up to 240-h testing under pure CO 2 sweep gas. • The maximum oxygen flux of 2.15 mL min−1 cm−2 obviously surpasses the traditional membrane. Cobalt-free mixed ionic and electronic conducting (MIEC) oxygen permeation membrane is a kind of promising materials for advanced air separation technology. However, its low oxygen permeability limits its practical application. In this work, we successfully prepared a type of La 0.8 Ca 0.2 Fe 0.94 O 3-δ -0.05Ag (LCF-Ag) hollow fiber membrane with "three-layer sandwich" structure by using a combined one-step sintering and phase conversion technology. Under the same experimental conditions, the oxygen permeation flux of the membrane structure was 1.79 times that of the traditional membrane structure, and the maximum oxygen flux was achieved at 2.15 mL min−1 cm−2. The model fitting proved that the membrane with new structure can effectively reduce the resistance of bulk diffusion. The stability test of oxygen permeation flux was carried out alternately in pure He and CO 2 atmosphere. The membrane displays high stability during the long-term operation of 240 h. Despite the oxygen flux had decreased slightly when CO 2 was used as sweep gas due to chemical adsorption of CO 2 to occupy the active sites on the membrane surface. The oxygen flux could be fully recovered once sweep gas switching to He, which indicates that the perovskite structure was not been damaged due to its good chemical stability. These results prove the feasibility of the new membrane structure for oxygen separation with CO 2 resistance, which may expand their applications to membrane reactors where the presence of CO 2 is not avoidable. [ABSTRACT FROM AUTHOR]