Structural Regulation Of Iron-Based Sulfide Oxygen Carriers And Enhancement Mechanism For Chemical Looping Combustion

Carbon emissions associated with fossil energy account for 89%of China’s total carbon emissions,and its efficient and low-carbon utilization is an inevitable requirement for achieving the goal of carbon neutrality.Chemical looping combustion has the advantages of energy cascade utilization and In-situ separation of CO₂,and is one of the important directions of low-carbon utilization of fossil energy.Among them,the design of oxygen carriers with high oxygen load,excellent kinetic properties and reproducibility is the key and main challenge to support the commercial application of chemical looping combustion technology.In this paper,aiming at the bottleneck of the traditional high oxygen load oxygen-loader-sulfate oxygen-carrier intrinsic structure regulation,this paper proposes an idea of regulating the intrinsic structure based on iron-based sulfide doping.Different sintering temperatures,precursor types and proportions were used to achieve controllable synthesis and intrinsic structure control.The structure-activity relationship was established by comparing the conversion efficiency of different sulfate oxygen-loaded gases.Combined with a variety of characterization methods,the migration path of oxygen and sulfur ions of oxygen-carrying gas was analyzed,and the mechanism of structural regulation and synergy enhancement reactivity and reproducibility was clarified,so as to realize the directional strengthening of the combustion process of chemical looping.The main research contents and conclusions are as follows:Firstly,the effects of sintering temperature and precursor on the crystal structure of CaFeSO oxygen-carrier were explored,and it was found that the sintering temperature had a significant effect on crystal nucleation and growth,and the crystal structure gradually changed from irregular aggregates to layered structure with the increase of temperature.The composition and ratio of precursors are also important factors affecting the crystal structure,and an appropriate increase in the content of iron atoms is conducive to the formation of CaFeSO structure.The characterization of crystal structure and electronic structure showed that the constructed CaFeSO lattice stripes were neat and regularly distributed,stacked layer by layer,and the average size was about 50-80 nm,in which Fe and O atoms were active in the bulk phase and S atoms were relatively active.By adjusting the temperature,atmosphere,precursor type and ratio,a thermally induced CaFeSO oxygen carrier synthesis strategy was established,and the synergistic regulation of crystal structure and electronic structure was realized.Secondly,by comparing CaFeSO with other sulfate oxygen carriers,it was found that the average CO conversion efficiency of CaFeSO oxygen carriers was only reduced by 15%after ten cycles,and showed good reactivity at low temperature,and the average CO conversion efficiency could be maintained at about 80%.In addition,CaFeSO oxygen carrier still has obvious layered crystal form after multiple cycle tests,and no problems such as melting and agglomeration are found,and the crystal phase of the system after reaction is mainly composed of Ca₂Fe₂O₅,CaFeSO and Ca S,and Ca O does not appear,showing excellent reactivity and reproducibility.Thirdly,through the characterization methods of programmed temperature reduction/oxidation,In-situ XPS and In-situ XRD,the study of the change of intrinsic characteristics before and after the oxygen carrier reaction shows that the internal oxygen atoms of CaFeSO oxygen carrier have three chemical states:lattice oxygen,surface oxygen and oxygen vacancies,which have a large oxygen storage capacity and strong oxygen transport capacity,and the reduction reaction can be completed at a lower reduction temperature,and the reduction process follows:Ca SO₄,Ca₂Fe₂O₅→Ca S→CaFeSO.For the oxidation stage,CaFeSO oxygen carriers consume less oxygen at lower oxidation temperatures to complete their regeneration,and the oxidation process follows:CaFeSO→Ca₃Fe₄S₃O₆→Ca S,Ca₂Fe₂O₅→Ca SO₄.The mechanism of CaFeSO oxygen carrier oxygen and sulfur ion migration and conversion was analyzed,and the mechanism of structural regulation synergistic enhancement reactivity and reproducibility was further elucidated.