Study On Chemical Looping Coupling Production Of Hydrogen And Syngas Based On Ni/Fe Composite Oxygen Carriers

Energy sustainability and pollution are the main challenges for the economic and social development of the world today.Biomass energy has become the future direction of energy development,attributed to the characteristics of rich resources,carbon neutrality,and renewability.Hydrogen and syngas have long been indispensable basic raw materials for the chemical industry.But more than 85%of the hydrogen and syngas production comes from the steam reforming of methane.The high energy consumption and unsustainability have determined the development of new processes was inevitable.The chemical looping coupling production of hydrogen and syngas can satisfy co-produce hydrogen and syngas in one process,and the efficient conversion and energy utilization has attracted much attention.Therefore,the chemical looping coupling hydrogen and syngas production based on carbon-neutral fuel-bio-oil is a green and sustainable technology.The oxygen carriers are the soul of chemical looping technology.Fe-based and Ni-based oxygen carriers are also known as the two most promising oxygen carriers in the 21st century.Thus,this paper was based on the Ni/Fecomposite oxygen carrier to evaluate the performance of chemical looping coupling hydrogen and syngas production,and explore the process parameters and the modification.The main investigation contents and conclusions were as follows:（1）Based on Ni/Fecomposite oxygen carriers with distinct degrees of NiO modification,fixed-bed testing and the characterization analysis of XRD,H₂-TPR,SEM before and after the reaction of oxygen carriers were carried out.It was found that the formation of NiFe₂O₄ structure was the key to the enhancement of the oxygen carrier reaction activity,but the excessive loading of NiO would cause agglomeration and sintering,reduce the oxygen carrier reduction performance,and affect the quality of hydrogen and syngas.Besides,the loading of NiO was closely related to the formation of carbon deposits.An appropriate loading of NiO was conducive to reduce the formation of graphitic carbon,but the excessive loading of NiO would aggravate the formation of graphitic carbon and affect the activity of the oxygen carriers.In this article,20%NiO loading was the best.（2）For the Ni20Fe80 oxygen carrier loaded with 20%NiO,the process of oxygen supply coefficient,reaction temperature,and steam-oil ratio was explored.Besides,5cycles of test performance were carried out under the optimal conditions.The results showed that the co-production of hydrogen and syngas had the best performance with the oxygen supply coefficient of 0.55,the reaction temperature of 900°C,and the steam-oil ratio of 1.2.The maximum syngas yield was 1.78Nm³/kg,as the syngas purity was close to 80%,and the H₂/CO was 2.At this time,the hydrogen purity was 95.6%,and the hydrogen yield was 0.69 Nm³/kg.However,Ni20Fe80 showed phase separation and the negative phenomenon of pore structure collapsed during the cycles.After 5 cycles,the hydrogen yield dropped to 0.45 Nm³/kg as the hydrogen purity dropped to 92%.（3）To improve the defects of Ni20Fe80 oxygen carrier with poor cycle performance,selecting the modified metals of CeO₂,ZrO₂,and Al₂O₃ for modification optimization investigation.The results concluded that the high O^2-migration characteristics of CeO₂and the formation of CeFeO₃ further improved the selectivity to syngas and maintain stable cycle performance.The maximum syngas yield up to 2.01.Nm³/kg,and the purity of syngas was close to 81%;the purity of hydrogen was more than 96%,and the hydrogen yield was 0.72 Nm³/kg.Although The doping of ZrO₂ improved the cycling stability of the oxygen carrier,ZrO₂ was an inert carrier and did not participate in the reaction,influencing the quality of hydrogen and syngas.The doping of Al₂O₃ would deprive the iron element in NiFe₂O₄at the cyclic reaction process,forming a large amount of FeAl₂O₄and AlFe₂O₄ structures,and reducing the hydrogen production performance of the oxygen carrier.The minimum hydrogen yield was only 0.3 Nm³/kg.（4）The migration property of ferric ion was also studied on the oxygen carriers doped with three modified metals of CeO₂,ZrO₂,and Al₂O₃.The results showed that the surface of ferric ion molar ratio of the Ni15Fe60Ce25 oxygen carrier increased from 66.5%to 72.84%in 5 cycles,compared with the Ni15Fe60Zr25 and Ni15Fe60Al25 oxygen carrier.Therefore,the Feelement was easier to be reduced and oxidized by the steam,more conducive to hydrogen production.