Study On The Preparation And Reaction Performance Of Cu-based Oxygen Carriers For Chemical Looping Combustion

Coal is our country’s main energy source.The massive use of coal caused the atmospheric CO₂ concentration to rise which leaded to environmental problems such as the greenhouse effect and melting glaciers and rising sea levels.So the development of efficient CO₂ capture technology was urgent.The chemical-looping with oxygen uncoupling（CLOU）process was a new type of combustion technology that can effectively capture CO₂ with low energy consumption,and can effectively reduce the emission of sulfur and nitrogen pollutants.The development of oxygen carrier was the key of the CLOU.Cu-based oxygen carrier has the charceteristics of high reactivity and high oxygen-carrying capacity,but the melting point of Cu O was relatively low,and sintering and agglomeration were likely to occur during the CLC process,which would cause its reactivity to decrease or even completely inactivate.Therefore,in this paper,the reaction activity,stability and reaction kinetics of copper-based oxygen carriers were studied.Four Cu-based bimetallic OC（80Cu20Mn,40Cu60Fe,60Cu40Co and 60Cu40Ni）were prepared by sol-gel method in this work.The oxygen release and adsorption behavior and Chemical looping combustion（CLC）behavior with gaseous and char of the OCs were examined.The oxygen transport capacity remained stable for 80Cu20Mn,40Cu60Fe and 60Cu40Ni,but a remarkable decrease was observed for 60Cu40Co.For the CLC tests with gaseous fuel,only 80Cu20Mn exhibited stable CO conversion,while the other three OC showed reducing CO conversion in the redox cycles.It was found that both 60Cu40Co and 60Cu40Ni were sintered and insufficient oxidation was confirmed after CLC with 11.3%CO/N₂ through XRD and SEM.In the CLC with char,all the OC significantly enhanced carbon conversion((3),reaction rate()as well as CO₂ selectivity((4₂).However,thedecreased during the cycle,indicating that the activity of the oxygen carrier decreased,of which 80Cu20Mn decreased the least,showing the best stability.Agglomeration,sintering,transformation of active components into composite salts such as Cu Fe₂O₄ and Cu Mn O₂ and deposition of ash were responsible for the deteriorated performance of the Cu-based bimetallic OC.At the same time,through isothermal kinetic experiments and theoretical calculations,it was found that the reduction processes of 80Cu20Mn and 60Cu40Co oxygen carrier with CO gas follow the shrinking nucleus model,and the integral form of the mechanism function is(（3）=1-（1-）^3/4.However,the reaction mechanism of 40Cu60Fe has changed.The first step of reaction process follows the shrinking geometry（cylindrical symmetry）model,and the integral form of the mechanism function is(（3）=1-（1-）^1/3.The activation energies of the reaction of 80Cu20Mn、60Cu40Co and 40Cu60Fe were 10.01 k J/mol,22.91 k J/mol and 11.38k J/mol.Due to sintering of the 60Cu40Ni oxygen carrier,its reaction mechanism had changed,which could’t be described by the same model.