Preparation And Property Of Symmetrical Dual-Phase Composite Membrane With Straight Open Pores

Oxygen transport membranes(OTMs),possessing both oxygen ion conductivity and electronic conductivity at elevated temperatures,can selectively allow oxygen to permeate through the membrane in the form of oxygen ions.Oxygen separation technologies based on OTMs have potential economic and environmental benefits.The OTMs hold promise to reduce the oxygen production cost by-30%compared to the traditional cryogenic distillation process.When the oxygen permeation process coupled with the oxidation-related reaction,it is expected to improve the conversion rate,and selectivity of high value-added chemicals.Meanwhile,OTMs can be applied to oxy-fuel combustion.Not only is it expected to show a net energy savings of 35%,but also to obtain flue gas containing high concentration of CO2,easy to separate,and capture CO2.In order for OTMs to become commercially applicable,not the membrane materials are required to have desired oxygen permeation flux,excellent chemical and thermal stability,high mechanical strength,and other properties,but also an efficient preparation technique is indispensable.Compared to single-phase OTM materials,dual-phase composite membrane materials have better long-term stability,higher mechanical properties,and wider design and application windows,making them easier to meet harsh requirements.Dual-phase composite membrane materials are expected to get practical application first.Two strategies are proposed to improve the oxygen permeation flux of the membrane.One is to thin the thickness of OTMs to shorten the oxygen ion diffusion path,the other is to improve the surface oxygen exchange rate through surface modification,and the configurations of OTMs based on porous support layer-dense separation layer are developed.The phase inversion tape casting method can prepare materials having gradient pore structures in one step.The finger-like straight pores they have are beneficial to reducing the transportation resistance.The results of our previous work show that OTMs prepared through such method possess higher oxygen permeability compared to the one prepared by conventional tape casting method;and this method is expected to be used to support the large-scale application of OTMs because of efficiency and inexpensiveness.This thesis is devoted to developing the configuration of OTM based on phase inversion tape casting method,and developing the preparation method that can be used for large-scale preparation of symmetrical OTMs.Chapter 1 introduces the working principle of OTMs,the status and the developing trends of membrane materials as well as the configuration and the relevant preparation technologies of OTMs.The research content of this thesis is proposed as well.In chapter 2,symmetrical Gd0.1Ce0.9O2-?-La0.6Sr0.4FeO3-?(GDC-LSF)dual-phase OTMs with straight open pores were prepared through a technique combining phase inversion tape casting,conventional tape casting and warm pressing.The surface of the GDC-LSF membrane was modified with Nd2NiO4+?(NNO)nanoparticles via impregnation technique.The oxygen permeability of membranes before and after surface modification was investigated.The result shows that NNO nanoparticles can dramatically enhance the surface oxygen exchange kinetics of the membrane.After impregnation with NNO,the oxygen permeation flux of the membrane increases from 0.38 mL·cm-2·min-1 to 1.53 mL·cm-2·min-1,under 900?and Air/He gradient conditions.The symmetrical configuration makes the membrane have a uniform stress distribution during the sintering process,endowing the membrane with high flatness and good thermal shock resistance.The symmetrical GDC-LSF membrane exhibits desired oxygen permeability,excellent thermal shock resistance,high mechanical property and satisfactory CO2 durability,promising for practical applications.In chapter 3,the technique developed in chapter 2 was used to prepare symmetrical Zr0.84Y0.16O1.92-La0.8Sr0.2MnO3-?(YSZ-LSM)dual-phase OTMs.Ce0.8Sm0.2O2-?(SDC)or NNO nanoparticles were impregnated on to the surface of the membrane.The oxygen permeability of membranes before and after surface modification was investigated.The result shows that the oxygen permeation flux of YSZ-LSM membrane without modification is 0.249 mL·cm-2·min-1 under 900? and Air/He gradient conditions.After impregnating with SDC or NNO,the oxygen permeation flux is increased to 0.323 mL·cm-2·min-1 and 0.554 mL·cm-2·min-1,respectively.The oxygen permeability of the membrane can be enhanced drastically through surface modification.Compared to SDC,NNO nanoparticles have a more significant effect on oxygen permeability of the membrane.The preparation technique can provide insights for the large-scale application of OTMs and the design and preparation of ceramic membranes used in other fields.In chapter 4,the summary of this thesis is presented,and the research prospect of the design and assembly of OTM devices is proposed as well.