Study On The Performance Of Chemical Looping Oxidative Dehydrogenation Of Ethane To Ethylene Based On Bimetallic Oxygen Carriers

Ethylene is an essential building block for many chemical industries,such as polyethylene,styrene,polyvinyl chloride,and ethylene oxide and its annual production is regarded as an indicator of the development level of the petrochemical industry in a county.Compared with traditional steam thermal cracking with high energy consumption and high pollution,oxidative dehydrogenation is an exothermic reaction and can overcome thermodynamic limitations,providing a new solution for the production of ethylene.However,the high cost of oxygen source,deep oxidation,and potential safety hazards bring new challenges to oxidative dehydrogenation.Chemical looping oxidative dehydrogenation（CL-ODH）uses the lattice oxygen of the oxygen carrier as the oxygen source to overcome the problems caused by molecular oxygen oxidative dehydrogenation,which has attracted wide attention from researchers.Oxygen carrier is a prerequisite for the realization of the chemical chain process.In this paper,bimetal oxide is used as the oxygen carrier,and its performance and mechanism of ethane oxidative dehydrogenation have been investigated.Firstly,86 kinds of bimetal oxides were screened by thermodynamic simulation software,and the oxygen carriers with controllable oxidation ability were screened out.The thermogravimetric experiment and the fixed-bed pulse experiment are used to explore the oxygen carrying capacity and oxidation capacity of the bimetal composite oxygen carrier.Among them,Ca Fe₂O₄,Ca₂Fe₂O₅ and Co Fe₂O₄ three kinds of bimetallic composite oxygen carriers have higher oxygen carrying capacity,which is beneficial to the chemical-looping combustion of ethane at a high reaction temperature;Ni Cr₂O₄ and Co Cr₂O₄ bimetallic composite oxygen carriers have a higher oxygen carrying capacity.The thermal cracking reaction has a high catalytic effect.The Cu Mn₂O₄ bimetallic composite oxygen carrier has high reactivity（70.5%）and high oxygen capacity（13.5wt.%）is a potential oxygen carrier for ethane chemical-looping oxidative dehydrogenation.Secondly,the Na₂WO₄/Cu Mn₂O₄ bimetallic composite oxygen carrier with core-shell structure was prepared,and at the same time,high oxygen capacity（12.5wt.%）,high conversion rate（56.4%）and high selectivity（90.0%）were realized.The core-shell structure of fresh oxygen carriers and surface morphology were characterized by SEM,H-TEM,H₂-TPR,XRD and SEM-Mapping.In the fixed bed pulse experiment,the Na₂WO₄/Cu Mn₂O₄ bimetallic composite oxygen carrier showed excellent oxidation reactivity.In the ten redox cycle experiments,the excellent cycle performance of the oxygen carrier was confirmed.Finally,the reaction mechanism and kinetic analysis of Na₂WO₄/Cu Mn₂O₄bimetallic composite oxygen carrier are carried out.The morphology and structure of the oxygen carrier after different pulse times were characterized by XRD,SEM and H-TEM.Studies have shown that Cu Mn₂O₄ oxygen carrier provides lattice oxygen,and Na₂WO₄ covering the surface of Cu Mn₂O₄ oxygen carrier prevents direct contact between Cu Mn₂O₄ oxygen carrier and ethane,thereby changing the ethylene selectivity of Cu Mn₂O₄ composite oxygen carrier.The isothermal method was used to study the kinetics of Na₂WO₄/Cu Mn₂O₄ bimetallic composite oxygen carrier.The Flyn-Wall-Ozawa and Doyle kinetic methods were used to obtain the oxygen release reaction kinetics of Na₂WO₄/Cu Mn₂O₄ bimetallic composite oxygen carrier.Finally,it is determined that the reaction order of Na₂WO₄/Cu Mn₂O₄ bimetallic composite oxygen carrier is 2.87,the reaction model is a random nucleation model（n=2）,the activation energy is 40.5 k J/mol,and the pre-exponential factor is 159.6.