Development And Performance Study Of Novel CO₂-Tolerant Dual-Phase Oxygen Permeable Membrane With High Flux

In the context of "double carbon target",the demand for pure oxygen in the energy sector is increasing day by day.Mixed conductor oxygen permeable membrane is a kind of inorganic dense ceramic membrane with mixed conductivity of both oxygen ions and electrons,which is attracting attention because it can separate pure oxygen from air with high selectivity.However,the trade-off between the stability and permeability of oxygen permeable membranes has been a bottleneck in their industrial application.The IC-MIEC type dual-phase oxygen permeable membrane,which consists of fluorite material for ionic conducting（IC）and perovskite material for mixed ionic-electronic conducting（MIEC）,has become a research hotspot in recent years because it shows superior stability under harsh atmospheres such as CO₂ compared to the single-phase perovskite type oxygen permeable membrane.However,the oxygen ion conduction limitations prevalent in dual-phase membranes still prevent them from meeting industrial oxygen permeability requirements.Therefore,it is of great significance to develop a novel oxygen permeable membrane with high flux and stability,and systematically investigate the influence law and mechanism of various factors on permeability in the process of oxygen separation to promote its industrial application.The fluorite phase is the main conductor of oxygen ion conduction in IC-MIEC type dual-phase oxygen permeable membrane.Enhancing its conductivity and electron conductivity not only weakens the oxygen ion conduction limitation in dual-phase membrane,but also extends the triple phase boundary（TPB）where oxygen surface-exchange reaction（OSER）occurs to the whole membrane surface,and at the same time reduces the blocking effect of electron conduction in the fluorite phase.In addition,the addition of appropriate sintering aids to the fluorite material is accompanied by an improvement in conductivity behavior while reducing its higher sintering temperature.Based on the above theoretical basis,in this paper,a new type of dual-phase oxygen permeable membrane with high oxygen permeability and stability is developed from the perspective of material structure design,which is the most critical factor affecting membrane performance,and experimental studies are conducted to investigate the influence law and mechanism of different material modification methods on the performance of dual-phase membrane.Then,the effect of operating conditions on the oxygen permeability of dual-phase membranes,in addition to material factors,was revealed through the simulation of oxygen permeation process,and intuitively reflects the flow,heat and mass transfer situation during the oxygen transfer process,and the mechanism of oxygen component transport in the basin and the key influencing mechanism were deeply analyzed.Specific studies were conducted as follows:（1）Firstly,three sintering aids with different contents of Co,Cu and Fe were added to the Ce0.8Sm0.2O2-δ（SDC）fluorite phase by both Grain boundary selective segregation（GBS）and lattice solid solution（SS）.The aim is to investigate the influence laws and mechanisms of the addition method,type and content of sintering aid on the conductivity behavior of fluorite phase,so as to seek the best way to improve the conductivity behavior of fluorite phase and provide theoretical support for the development of novel dual-phase membranes.At the same time,the effect and mechanism of different sintering aids and addition methods on SDC fluorite materials were analyzed.The results show that the GBS method has a better enhancement effect on conductivity than SS method,and introduces more electronic conductivity.The SDC with the addition of 2 mol%co sintering aid has the highest total conductivity and mixed conduction capability.At 700℃ and 800℃,the total conductivity reaches 0.04 S·cm-1 and 0.09 S·cm-1,respectively.（2）The potential correlation and mechanism between fluorite phase conductivity behavior and dual-phase membrane performance were deeply resolved by combining SDC modified by sintering aids with Co-free perovskite material Cu0.2Fe0.8O3-δ-Sm0.5Sr0.5（SSCF）.The results showed that the oxygen permeation performance of the dual-phase membrane was positively correlated with the total conductivity and mixed conduction capabilityof the fluorite phase.The improved conductivity behavior of SDC results in enhanced mixed ion electron conduction（MIEC1）capability,which forms a dual-phase membrane with mixed conduction in both phases by combining with SSCF（MIEC2）which has mixed conduction capability.The developed MIEC1-MIEC2 novel dual-phase membrane 2Co-SDCSSCF has the highest oxygen permeability,reaching 1.21 mL·min-1·cm-2 at 950℃under He sweeping conditions,which is 17%higher than before the modification.The oxygen permeability decays to 0.78 mL·min-1·cm-2 after a long time stability test under CO₂ atmosphere.（3）To address the problem of performance degradation after long-term stability tests under CO₂ atmosphere,the SSCF of perovskite phase was modified by Nb doping to reveal the intrinsic mechanism of Nb doping to enhance the stability of perovskite,and the interaction between dislocation density and oxygen vacancies in ceramic oxygen permeable materials was elucidated by using SSCF as the research object.The results show that the configuration entropy and polarization impedance increase and the conductivity decreases after Nb doping,and the double exchange mechanism is followed before and after Nb doping.（4）For Nb doping modification,the stability of dual-phase membrane is improved,but the oxygen permeability is decreased.Firstly,the dual-phase membranes were further optimized by the dual element coordination method for A and B positions of perovskite phase.Then,the influence laws and principles of each modification method on the properties of dual-phase membrane materials and the effect of sintering system on the mechanical properties of dual-phase oxygen permeable membranes were systematically investigated,and applied it to a partial oxidation of methane（POM）membrane reactor.The results showed that Nb doping reduced the oxygen permeability of the dual-phase membrane under He atmosphere but significantly improved the structural stability and CO₂ tolerance.The properties were further optimized after coordinated optimization of the dual elements,and the oxygen permeability was stable at 0.82 mL·min-1·cm-2 after a long time test in CO₂ atmosphere.The results of the modification study for the IC-MIEC type dual-phase membrane proved the feasibility of the design method and enriched the oxygen permeable membrane design concept.（5）Based on the computational fluid dynamics（CFD）method,the oxygen permeation equations applicable to dual-phase membranes were compiled and linked in FLUENT software to establish a three-dimensional mathematical model of flow,heat and mass transfer describing the oxygen permeation process.A comprehensive analysis of the influence law and mechanism of different operating conditions on oxygen permeation performance was presented in addition to material factors,and the internal flow field,pressure field,temperature field and component distribution in the oxygen separation process were revealed in depth and intuitively,bridging the gap in simulation studies of oxygen transport processes in dual-phase membranes,providing theoretical support and technical guidance for its industrial application.The results show that the oxygen concentration accumulation at the peripheral corners of the permeate side and the resulting reduction in the oxygen partial pressure gradient are detrimental to the oxygen permeation performance,which can be improved by a reasonable structural design of the membrane separation device.