Activity Of Bismuth Oxide Promoted Iron-based Oxygen Carriers And The Mechanism Study

With people's attention to a series of serious problems such as global climate change and sea level rise,controlling CO₂ emissions has become the focus of attention of the world.As the world's largest CO₂ emitter,China urgently needs to develop economically viable large-scale CO₂ capture technology.Chemical-looping combustion?CLC?has the advantages of CO₂ separation and energy gradient utilization and is a CO₂ capture technology with great development potential.Oxygen carrier has important research significance as a key link in CLC.Because of its good thermodynamic properties,environmental protection,abundant reserves,and low cost,iron-based oxygen carriers are considered to be a type of oxygen-carrying body with promising industrial applications.However,its low reactivity has greatly limited its application in CLC.This article mainly focuses on the problem of low reactivity of iron-based oxygen carriers,according to oxygen release characteristics of oxygen carriers,studied on the effect of Bi₂O₃ additives on the activity of iron-based oxygen carriers and the mechanism of action.Firstly,Fe₂O₃/Al₂O₃ composite iron-based oxygen carriers with different calcination temperatures and different Bi₂O₃ loadings were prepared by sol-gel method.Using a mixed gas of CO and N₂ as reaction gas,the effect of calcination temperature,Bi₂O₃ loading,and reaction temperature on the reactivity of iron-based oxygen carriers was investigated using Thermo Gravimetric Analyzer?TGA?.The experimental results show that the sample after calcining at 1250°C has the highest reactivity with a loading of 10%Bi₂O₃,which is about 1.5 times more than the sample without Bi₂O₃;The reaction temperature has a great influence on the activity of the oxygen carrier.950°C is the most suitable temperature for the reaction of the oxygen carrier prepared in this article.In order to further explore the performance of the new iron-based oxygen carrier,a fluidized bed experiment was conducted in a vertical tube furnace and it was found that the oxygen-bearing body sample added with Bi₂O₃ maintained a high continuous reaction capability during the reduction reaction,that is,they had better reaction stability.In addition,the experimental results of the fluidized bed are consistent with those of TGA.The reaction kinetics of the novel iron-based oxygen carriers was studied using the shrinking model theory.The calculated results showed that the oxygen-bearing body samples added with Bi₂O₃ reduced the activation energy of the reaction between the oxygen carrier and the CO,making the reaction easier and increasing the reactivity of the oxygen carrier;Through XRD,SEM,EDS,BET and other characterization methods,the influence of Bi₂O₃ promoter on the activity of iron-based oxygen carrier and the mechanism of action were analyzed in depth.The characterization results show that the addition of Bi₂O₃ additives partially destroyed the lattice of Fe₂O₃,resulting in lattice distortion,and formed a solid solution of iron oxide,but did not change the appearance of Fe₂O₃,and the specific surface area of the oxygen carrier did not change significantly;BiFeO₃,which has a perovskite structure,and a synergistic effect of the oxygen carrier of the bimetal oxide,is also the main reason why the Bi₂O₃ promoter can increase the activity of the iron-based oxygen carrier.