Preparation And Properties Of Ceramic Membranes For High Temperature Separation Of CO₂

Global excessive emissions of greenhouse gases,especially CO₂,make climate anomalies world wide.The technique of CO₂ emission reduction and capture has integrated all global focus.Especially,the power plant flue gas,which is the largest source of emissions,has become the main target for people to reduce emissions and capture of CO₂.Conventional CO₂ capture mostly used the organic membranes,but the operation temperature of the organic membranes is low and the selectivity of the organic membranes is low at high operating temperatures.So,it is very urgent that the new membrane materials are developed.Inorganic membranes are favored by people because of their high working temperature,good chemical stability and thermal stability.There are two research aspects in this paper,one is the preparation and performance of ceramic-melt carbonate dual-phase separation membrane for high temperature separation of CO₂;the other one is the preparation and performance studies of the proton-electron mixed conductor dense ceramic for high temperature conversion of CO₂.The yttria-doped zirconia?YSZ?with good oxygen ion conductivity,good chemical stability and high mechanical strength is selected as the oxygen ion conductor material under high temperature conditions,and the porous YSZ ceramic hollow fiber membrane is prepared by phase inversion combined with high temperature sintering technology;The YSZ-molten carbonate dual-phase membrane was obtained by loading the melted-carbonate into the porous YSZ membrane by an impregnation method.It was found that the composition of the core liquid is the key factor affecting the pore structure of the YSZ porous hollow fiber.The temperature and the flow rate of the sweep gas are important factors that affecting the separation performance.The experimental results of CO₂ separation performance show that the dual-phase membrane made of H₂O-C₂H₅OH-NMP mixed solution as the core liquid and YSZ sintered at 1550°C loaded molten carbonate,when the sweep gas flow rate is 100 mL min^-1 at 850°C,the flux of CO₂ can reach 0.22 mL?min^-1?cm^-2,and it can run steady at 700°C for 96 h.In this paper,La_0.6Sr_0.4Co_0.2Fe_0.8O_3-??LSCF?as oxygen ion-electron hybrid conductors with perovskite structure is studied.The preparation of the porous ceramic disk membrane,as well as the composition of the carbonate and the methods of the carbonates filtration,which affected the permeation of CO₂ are studied.The experimental results show that the permeation flux of CO₂ in LSCF-melt membrane is larger than that of YSZ-molten carbonate membrane;and there is a significant effect of thickness of LSCF porous membrane on the permeation flux of CO₂.When the thickness is 0.76 mm,the permeation of CO₂ at 850°C can reach 0.256 mL min^-1cm^-2.In order to reduce the membrane thickness,the LSCF porous hollow fiber membrane was prepared by phase inversion with high temperature sintering technology.The dual-phase LSCF-molten carbonate membrane was prepared by high temperature impregnation.The preparation process of LSCF hollow fibers membrane and dual-phase membrane was optimized.The influence of operating conditions on the permeation flux of CO₂ was investigated.It was found that the CO₂ permeation flux of the hollow fibers is 0.061 mL min^-1 cm^-2 at 500°C,and it reaches 0.876 mL min^-1 cm^-22 at 850°C,three times to the CO₂ flux of the disk membrane.The CO₂permeation stability test showed that the membrane has good thermal shock resistance and mechanical stability.According to the characteristics of the CO₂ dual-phase membrane permeation process,the physical model and mathematical model of the carbon dioxide dual-phase membrane permeation process were established on the literature.The simulation is performed using a mathematical model and the experimental results.According to the simulation,it is found that pre-equilibration is required before the carbon dioxide dual-phase membrane is premeated by CO₂.According to the simulation results,this paper proposes that there will be obvious potential changes on both sides of the membrane during the carbon dioxide permeation process.The open circuit potential can be directly measured by the voltmeter.This potential difference can reflect the effection of the reaction temperature and the partial pressure of CO₂.It is useful for the experiments and the application of technique of CO₂ dual-phase membrane.In the second aspect of this paper,the high temperature conversion of CO₂ into a more valuable chemical product is discussed.This chapter proposes the reverse water gas shift reaction?RWGS?using a proton membrane of perovskite structure.In the experiment,5 wt%Ti₄O₇-doped SrCe_0.9Y_0.1O_3-??SCY?ceramic powder?SCY-Ti for short?was used to make a multiphase mixed conductor hollow fiber dense membrane.It was assembled into a reactor to investigate the performance of the reaction that H₂ reduction CO₂.It was found that the SCY-Ti membrane itself has catalytic properties,and the reactor assembled with the modified membrane with SCY-Ti powders has the higher reaction performance.In the case of simulating waste hydrogen as a hydrogen source and simulating CO₂ off-gas as a raw material,the CO yield was 15.02%at 900°C.And the reactor was continuously operated to conver CO₂ to CO for 145 h,and its performance was steady.This provides an experimental basis for future waste hydrogen treatment and CO₂ conversion.