Preparation And Property Of B-site Doped Mixed Conducting Oxygen Permeable Membrane

The mixed-conducting oxygen permeable membrane is a kind of oxygen separation inorganic ceramic membrane with the conductivity of both oxygen ion and electronic at a high temperature. The partial oxidation of CH4 in coke oven gas(COG) to hydrogen in a mixed ionic-electronic conducting(MIEC) ceramic membrane reactor has been showing a great application prospect in the comprehensive utilization of existing resources to alleviate the energy crisis. Meantime, Oxy-fuel combustion based on the MIEC oxygen permeable membrane is the most promising technology for CO2 capture. High oxygen permeability and excellent stability are both requried for MIEC membrane to realize the practical application. In this thesis, the effect of Zr-doped content in the B-site on the oxygen permeability and stability of perovskite-typed oxides Ba Co0.7Fe0.3-x Zrx O3-d was systematically investigated. In addition, the effect of different doped elements in the B-site of electronic-conducting phase on the properties of Ce0.8Gd0.2O2-d-Ba0.95La0.05Fe0.9M0.10O3-δ dual-phase membrane was also studied in this work.A series of mixed ionic-electronic conducting materials, Ba Co0.7Fe0.3-x Zrx O3-δ(x = 0 ~ 0.12) were successfully synthesized with a sol–gel method. Effects of zirconium content on the properties of these membrane materials were systematically studied. A pure cubic perovskite structure was obtained for BCFZ membrane materials with an appropriate amount of zirconium(x = 0.04 ~ 0.10). The grain size of the samples gradually decreases with increasing zirconium content. The structural stabilities of the membranes in different atmospheres(H2, O2 and CO2) are significantly improved by substituting an appropriate amount of iron by zirconium. However, increase of the zirconium content also leads to a decrease in the electrical conductivity, which is confirmed by the first principles calculations and experiment results.The oxygen permeation performance of BCFZ membranes under pure He, CO2-containing, COG atmospheres was systematically studied using a home-made equipment. The oxygen permeation performance of BCFZ membrane shows prodigious difference in three atmospheres. Under a pure He atmosphere, with increasing the zirconium content, oxygen permeation flux of the membranes increases and reaches a peak at x = 0.06, and then decreases. All the the oxygen permeation fluxes drops gradually with the prolongation of time at the low temperature(￡ 800 °C). Under a CO2-contining atmosphere, BCFZ membranes show serious degradation of oxygen permeation fluxes and structure. Under a COG atmosphere, the oxygen permeation fluxes of all the membranes were considerably higher than that under a pure He atmosphere. Among all the samples, the good long-term operation stability and highest permeation flux of 18.3 ml min-1 cm-2 at 900 °C under an air/COG gradient were achieved in the Ba Co0.7Fe0.24Zr0.06O3-δ membrane reactor.Expanding sintering time improves the grain growth of the BCFZ and has no obvious influence on the phase structure. For BCFZ membrane materials, the grain bulk of the BCFZ membranes is a faster path for oxygen ion diffusion and the grain boundary acts as a barrier. Hence, samples with larger grain sizes have remarkably higher oxygen permeation fluxes. Comprehensive analysis of the results indicates that the oxygen permeability depends on the combined effect of the oxygen vacancy concentration, grain size and electrical conductivity, which are affected by the zirconium content.A series of dual-phase membrane materials with a composition of 60 wt% Ce0.8Gd0.2O2-δ-40 wt% Ba0.95La0.05Fe0.9M0.10O3-δ(CGO-BLFM0.10, M = Fe, Nb, Zr, Zn, Sc, Y) were successfully synthesized with a sol-gel method. All BLFM0.10 oxides show a pure cubic perovskite structure. There is no chemical reaction between CGO and BLFM0.10, indicating very good chemical compatibility. Oxygen permeation fluxes under a pure He atmosphere follow the order: CGO-BLF > CGO-BLFZn0.10 > CGO-BLFY0.10 > CGO-BLFZr0.10 > CGO-BLFNb0.10 > CGO-BLFSc0.10. Under a CO2-contining atmosphere, oxygen permeation fluxes show a decrease compared that under a pure He atmosphere. Among them, CGO-BLFSc0.10 showed the best oxygen permeation stability under a pure CO2 atmosphere. CO2-corrosion on the perovskite phase is the main reason for the damage of the property of fluorite-perovskite-typed dual-phase membrane materials in CO2 atmosphere, and improving CO2-corrosion resistance of electronic phase of perovskite materials can effectively enhance the stability of dual phase membrane materials.