Study On The Regulation Effect Of Perovskite-Type Oxygen Carrier A/B Metal On The Production Of Ethylene From Ethane Through Chemical-Looping Oxidation Reaction

There is about 10%ethane in natural gas and shale gas,and the use of oxidative dehydrogenation to produce ethylene is of great significance to alleviating the oil crisis.Chemical looping oxidation has been applied to the oxidation of ethane due to its moderate oxidizability and low product throughput,and the oxygen carrier is the key to this method.Perovskite oxygen carriers are used in chemical looping oxidation due to the flexibility of A/B site metals,good oxygen storage-release performance,and low cost.However,there is a problem of low ethylene yield when reacting with ethane.Therefore,it is important to obtain the ABO₃with the best response effect and further improve its performance through the regulation of radius and valence,and to find out the internal factors that affect its performance.Using citric acid complexation method to prepare different ABO₃,A_1-xAˊ_xBO₃,AB_1-yBˊ_yO₃and A_1-xAˊ_xB_1-yBˊ_yO₃perovskite-type oxygen carriers.Study the effect of different A/B position metals on the oxygen carrier ethane reaction performance,and obtain the oxygen carrier with the best reaction performance.Through the A/B-site metal doping,the influence of the radius,valence state,doping ratio of the A-site doped metal and different B-site doping metals and ratios on the oxygen carrier reaction performance was investigated.Through XRD,SEM,O₂-TPD,XPS and other characterization methods,the oxygen carrier crystal phase composition,apparent morphology,oxygen release performance and composition of different elements were analyzed,and then the internal factors affecting the reaction performance were obtaine.The main conclusions are as follows:（1）The oxygen carrier ABO₃with the best ethane reaction performance was obtained,and the factors affecting its continuous reaction performance and cycle stability were explored.1)When different A/B-site metals form the perovskite oxygen carrier,BaCoO₃has the best reaction performance with ethane.The conversion rate of ethane is 60%,the selectivity of ethylene is 75%,and the yield of ethylene is 46%.2)Surface adsorbed oxygen and lattice oxygen divide the oxidation of ethane into two stages.The surface adsorbed oxygen completely oxidizes ethane to CO₂and H₂O in the initial stage,and then lattice oxygen dehydrogenates ethane to produce ethylene.The reaction time of lattice oxygen is 80 minutes,and the relatively high proportion of Co³⁺enables the reaction to have a high ethylene yield.3)After 12 cycles of BaCoO₃,the specific surface area and pore diameter are slightly reduced,which reduces the conversion of ethane by about 4%,the ethylene selectivity is almost unchanged,and its cycle stability is good.（2）The influence laws and internal factors of different valence states of A-site metal radius and ratio regulation,and different B-site metal ratio regulation on the ethane reaction are obtained.1)The A site is doped with divalent metal,and the oxygen carrier reaction performance has not been improved.For trivalent metal doping,as the radius of the doped metal increases,the ethane conversion rate first increases and then decreases.As the doping ratio increases,the ethane conversion rate first increases and then decreases,and the ethylene selectivity gradually decreases.When the B-site metal is adjusted,the ethylene yield is better when Cu doped.As the doping ratio increases,the ethylene yield first increases and then decreases.2)The higher the ratio of lattice oxygen in the oxygen carrier,the greater the ethane conversion rate;the higher the Co³⁺content,the greater the ethylene selectivity.3)When the oxygen carrier doping ratio is too high,the doped metal will not be able to enter the oxygen carrier,resulting in a decrease in the oxygen carrier reaction performance,and the reaction performance of A site doping with 30%La and B site doping with 20%Cu is improved.（3）The A/B site metal co-doping adjustment improves the Ba_0.7La_0.3Co_0.8Cu_0.2O₃reaction performance and improves the cycle stability.1)The ethane conversion rate increased by about 7%,the ethylene selectivity increased by about 5%,and the ethylene yield increased by about 7%to 53%.2)The temperature of adsorbed oxygen on the surface of the oxygen carrier and the release temperature of lattice oxygen decreases,and the action time of lattice oxygen becomes longer,increasing to 94 min.The increase in the ratio of lattice oxygen/surface adsorbed oxygen and the ratio of Co³⁺/Co²⁺results in the improvement of the co-doped oxygen carrier ethane reaction performance.3)After 12 cycles,the oxygen carrier can still restore the perovskite crystal form.The slight decrease in specific surface area and pore diameter reduces the conversion of ethane by only about 2.5%,the selectivity of ethylene is almost unchanged,and the yield of ethylene is only reduced by about 1.5%.