Preparation Of SDC-SSF Layered Dual-phase Oxygen Permeable Membrane And Research On Its Oxygen Permeability

Ceramic oxygen permeable membranes have important applications in the fields of pure oxygen separation,partial oxidation of methane and oxyfuel combustion.The key to achieving this is to prepare oxygen permeable membrane modules with high stability and high oxygen permeability.Compared with single-phase perovskite oxygen permeable membrane,fluorite-perovskite two-phase oxygen permeable membrane has higher stability,but lower oxygen permeability.In this thesis,based on the high stability biphasic oxygen permeable membrane,the supporting structure was constructed by two-sided etching method,and the supporting biphasic oxygen permeable membrane was prepared.Based on Ce_0.85Sm_0.15O_2-??80 wt.%?-Sm_0.6Sr_0.4FeO_3-??20 wt.%??SDC-SSF?dual-phase oxygen permeable membrane base membrane,different thicknesses were prepared by double-sided etching.SDC-SSF supported dual phase oxygen permeable membrane.The SDC-SSF supported dual-phase oxygen permeable membrane was characterized by XRD,SEM and EDS.It was found that the SDC-SSF base membrane was acid-etched to form a three-layered structure of"porous layer?fluorite phase?-thin dense layer?fluorite phase/perovskite phase?-porous layer?fluorite phase?",the acid etching method can efficiently etch the SSF perovskite phase components in SDC-SSF dual-phase oxygen permeable membranes,and effectively retain SDC fluorite phase to form a porous support,the SDC-SSF oxygen permeable membrane which are calcined at 1450 ^oC have an uniform and dense surface.As the SDC-SSF membrane is immersed in concentrated hydrochloric acid solution for a period of time,the surface of the membrane gradually forms a porous structure,and the pore diameter gradually increases,and the thickness of the dense functional layer gradually decreases.As the etching time prolongs,the etching rate of the membranes is gradually slowed down.After 28 hours of etching,the thickness of the dense layer is only 158.3?m,and the entire film remains intact and uniform,without delamination or uneven pore distribution.Oxygen permeation test of SDC-SSF dual-phase oxygen permeable membrane showed that oxygen permeability of the oxygen permeable membrane material increased with the increase of temperature in a certain gas flow rate range;At the same operating temperature,the oxygen permeability increases with increasing gas flow rate.At 950 ^oC,the oxygen permeability without etching membrane is 0.33 ml·cm^-2·min^-1,after 28 hours of etching,the oxygen permeability reached 0.49 ml·cm^-2·min^-1.After 28 hours of etching,the rate-determining step of the oxygen permeation membranes is converted into surface exchange control from bulk phase diffusion.The activation energy of the membrne without etching is Ea?0 h?=46.99 kJ·mol^-1,and the activation energy is reduced to Ea?28 h?=22.45 kJ·mol^-1 after 28 hours of etching.In order to further increase the oxygen permeability of SDC-SSFsupported oxygen permeable membranes,the surface exchange resistance of SDC-SSF oxygen permeable membranes can be reduced by introducing high active catalysts in the porous layer of the double layers.In this thesis,an improved the oxygen permeability can be attained for SDC-SSF oxygen permeable membrane by loading Co and Pt catalysts in porous substrates.The metallographic microscope and SEM-EDS element analysis of the diaphragm showed that Co and Pt catalysts can be loaded into the double-sided SDC porous carrier,respectively.Furthermore,the oxygen permeability of the as-prepared membranes are investigated.At 950 ^oC,the oxygen permeability of SDC-SSF membranes loaded with Co catalysts reached 0.53 ml·cm^-2·min^-1.The oxygen permeability of the membrane loaded with Pt catalyst reached 0.81ml·cm^-2·min^-1.The SDC-SSF membranes loaded with Co and Pt showed no significant change in oxygen permeability within 50 hours.It is shown that the Co catalysts and the Pt catalysts are well coupled with the SDC porous carrier.Meanwhile,the rate-determining step of supported Co catalyst is the surface exchanging step,and the rate-controlling step of supported Pt catalyst membranes is converted into bulk diffusion from surface exchange.