Study On Characteristics Of Modified NiFe₂O₄ Oxygen Carrier In Methane Chemical Looping Hydrogen Production

The chemical looping hydrogen production technology is a potential hydrogen production technology.NiFe₂O₄ oxygen carrier is one of the oxygen carriers with the best comprehensive hydrogen production performance,but it still has shortcomings such as insufficient reaction stability and reaction activity.In this research,the hydrogen production performance and reaction stability of NiFe₂O₄ oxygen carrier are optimized and improved from three aspects:metal doping,inert carrier loading and reaction conditions optimization.First,the NiFe₂O₄ oxygen carrier was doped with Ce,W,and Sr by the sol-gel method.Through the chemical looping hydrogen production experiment,it was screened out that doped with 10wt%Ce-NiFe₂O₄ oxygen carrier has the highest hydrogen production.The chemical looping hydrogen experiment was carried out on NiFe₂O₄ oxygen carriers with different Ce doping contests,and the oxygen carrier with the highest hydrogen production was 6wt%Ce-NiFe₂O₄.HSC Chemistry thermodynamic simulation and characterization analysis results show that after Ce is doped into NiFe2O4 oxygen carrier,the content of spinel structure with higher reactivity in the oxygen carrier is greatly increased,thereby improving the reactivity and hydrogen production of the oxygen carrier;at the same time,the specific surface area of the oxygen carrier is increased after the metal Ce is doped,which is conducive to the full contact between the reactive gas and the active sites of the oxygen carrier in the CLH process,thereby promoting the gas-solid reaction.However,with the increase of Ce doping amount,Ce appears in a large amount in the form of Ce O₂in the oxygen carrier.Because the reactivity of Ce O₂ is lower than that of spinel structure,The increase of Ce O₂ will gradually reduce the hydrogen production of the oxygen carrier.Then,the NiFe₂O₄ oxygen carrier was loaded with Si O₂,Ti O₂ and Al₂O₃ by themechanical mixing method.Through the chemical looping hydrogen production experiment,it was screened out that doped with 50wt%Al₂O₃-6wt%Ce NiFe₂O₄ oxygen carrier has the highest hydrogen production.The chemical looping hydrogen experiment was carried out on 6wt%Ce NiFe₂O₄ oxygen carriers with different Al₂O₃ loading contests,and the oxygen carrier with the highest hydrogen production was 50wt%Al₂O₃-6wt%Ce NiFe₂O₄.At the same time,the reaction stability of the oxygen carrier was significantly improved,after 15 cycles keep the hydrogen production stable.The characterization analysis results show that the inert carrier Al₂O₃ can effectively increase the specific surface area of the oxygen carrier,which is conducive to the gas-solid reaction,thereby increasing the hydrogen production of the oxygen carrier.In addition,after the oxygen carrier is loaded with the Al₂O₃ inert carrier,Al₂O₃ is evenly coated on the spinel structure,which effectively prevents the collapse and loss of the spinel structure of the oxygen carrier in the cyclic reaction.At the same time,the loading of the inert carrier suppresses the agglomeration of active sites in the process of chemical looping hydrogen production,reduces the occurrence of sintering,and effectively improves the reaction stability of the oxygen carrier.Finally,the optimal experimental conditions of modified OC in chemical looping hydrogen production were screened.The optimal gel p H of the oxygen carrier is 7.5.The optimal reaction temperature of the CLH process is 850℃,the optimal deionized water injection volume is 0.05ml/min.Modification of oxygen carrier by metal Ce and inert carrier Al₂O₃,the hydrogen production of the oxygen carrier is increased,the content of Ce and Niin the oxygen carrier is reduced,and the economy of the chemical looping hydrogen production system is improved.