| The membrane made by mixed ionic and electronic conducting (MIEC) oxide can separate oxygen from air directly, when a difference of oxygen partial pressure (DOPP) passes through it at high or intermediate temperatures. Without the electricity circuit and with selectivity of 100% for oxygen, both make the MIEC membrane separation a promising method due to the simplification of membrane preparation and the convenience for its usage. This thesis investigated two key issues for the practical application of MIEC membranes. It included the preparation of membranes with large geometrical size, and the utilization of waste energy in metallurgical slag for MIEC membrane separation.Firstly, the recent progress on the MIEC materials was reviewed for its basic theory, new materials, and prospect of potential application. Their potential applications introduced included membrane separation for oxygen, cathode and anode materials for SOFC, and ceramic membrane reactor to produce the synthesis-gas from methane. Secondly, the preparation and characterization of resulting membranes was generally introduced. The phase compositions and microstructure of as-prepared membranes were investigated by XRD and SEM methods respectively. The oxygen permeability of resulting membranes was measured by steady method, and the total electrical conductivity of as-prepared samples was measured by 4 probe method using AC impedance apparatus.Considering the convenient sealing and assembling for tubular membrane, thirdly the tubular membranes of SrCo0.8Fe0.1Sn0.1O3-δ (SSCF) were prepared by extrusion and characterized on its phase composition, micro morphology, and oxygen permeation. It was found that the permeability of resulting SSCF membrane increased with the temperature and difference of oxygen partial pressure (DOPP) through it. At 900oC and a little DOPP of Po2(h) =0.209 atm·Po2(l) =0.12atm, the resulting SSCF tubular membrane had the permeability of 0.5×10-6mol·cm-2·s-1, moreover, the permeability of it kept unchangeable during the period of 160h operation.Fourthly, the SrCo0.8Fe0.2O3-δ tubular asymmetric membrane (TAM) was prepared by co-firing method and characterized for its phase composition, micro morphology, and its permeability. The resulting TAM sample was consisted by two layers: 1) a dense top layer of SrCo0.8Fe0.2O3-δ (SCF) with thickness of 50μm; and 2) a porous substrate layer of (SrCo0.8Fe0.2O3-δ)0.85(SrSnO3)0.15 (SCF-SS). As compared with the SCF and SCF-SS tubular symmetric membranes (TSM), the resulting TAM sample had an improved permeability, and they had the same geometrical size. At 900℃, the resulting SCF TAM sample had a permeability of 1.91ml.cm-2.min-1, and it was 31.7% and 47.4% higher than that of SCF and SCF-SS TSM samples respectively.Finally, for the utilization of waste heat of metallurgical slag to cut the cost of oxygen separation by MIEC membrane, a proto type separator combined with a high temperature air generator (HTAG, factually a fixed reaction bed) was setup. The separator was heated and fed by high temperature air (HTA), which was heated by the fixed reaction bed. The fixed reaction bed was consisted by grains of high temperature steel slag, and it heated the fluent cool air into HTA. In the separation experiments, the HTA heated the permeable membrane to 865℃when the 7 m3/h fluent air passed through the steel slag of 1050℃. Moreover, the resulting separator made by 3-membrane-assembling (SSCF tubular membrane with out diameter of 9.2 mm, wall thickness of 1.5 mm, and length of 140 mm) produced 34ml oxygen per minute at 865℃.Key w ords: perovskite-type oxide; mixed ionic and electronic conducting; oxygen... |
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