The Preparation And Reaction Performance Of The Catalyst For Ethane Lattice Oxygen Oxidative Dehydrogenation

Ethylene is an important petrochemical basic raw material,and its market demand is increasing year by year.Ethane dehydrogenation can convert low-value low-carbon alkanes into high-value-added olefins.Compared with catalytic dehydrogenation,the introduction of oxidant in oxidative dehydrogenation can break the restriction of thermodynamic equilibrium and effectively strengthen the conversion of alkane molecules.However,the presence of gaseous oxygen in the oxidative dehydrogenation process can easily lead to excessive oxidation reactions,which not only reduces the selectivity of olefins,but also presents safety hazards such as explosions.The lattice oxygen oxidative dehydrogenation process uses variable valence metal oxides as catalysts.The lattice oxygen is used in the reactor to selectively oxidize ethane into ethylene and water,and then the lattice oxygen is re-oxidized in the regenerator to supplement the lattice oxygen.It can not only achieve a breakthrough in the thermodynamic balance limit,but also avoid the peroxidation problem caused by gaseous oxygen,and has important research and application value.This dissertation is devoted to the development of high-efficiency ethane lattice oxygen oxidative dehydrogenation catalysts,using perovskite and iron oxide as the oxygen carriers,and carried out a series of research work from the catalyst composition,preparation method and process conditions.Firstly,the perovskite-type catalyst with good thermal stability was prepared.The elemental composition and preparation conditions of the catalyst showed that the lattice oxidation dehydrogenation performance was the best when the calcined temperature was 950^oC and the composition was La_0.6Sr_1.4Fe O₄.After the alkali metal Li is supported on the surface of the perovskite catalyst,the reducibility of the perovskite and the release rate of lattice oxygen are reduced,which can further increase the ethane conversion while ensuring the selectivity of ethylene.The optimized catalyst 0.5Li-La_0.6Sr_1.4Fe O₄ has an ethane conversion about 40%,an ethylene selectivity about 85%,and exhibits excellent stability in a continuous oxidation-reduction reaction cycle.In contrast,the initial reaction performance of Na modification is similar,but the stability is poor during the continuous reaction and regeneration process.Secondly,through the screening of a large number of metal oxides,it was found that iron oxide is a good oxygen carrier for lattice oxygen oxidative dehydrogenation,and the key to its application is to effectively inhibit the peroxide reaction at the initial stage of the reaction.Furthermore,a series of iron-based bimetallic oxide catalysts were prepared using alumina as a carrier.It was found that the introduction of W in the Fe-W bimetallic system weakened the reducibility of the catalyst and reduced the rate of release of lattice oxygen,which can not only inhibit the peroxidation reaction in the initial stage of the reaction,but also prolong the duration of reaction activity.On the optimized catalyst Fe-W/Al₂O₃（Fe₂O₃=20 wt%,Fe:W=6）,the ethane conversion is about 20%,and the ethylene selectivity is about 85%.Although the activity is lower than that of the perovskite catalyst,the activity time is prolonged,the ethane processing ability is greatly improved,and its reaction performance remains basically stable in the continuous oxidation-reduction reaction cycle.Finally,the reaction conditions of the above two catalyst systems were optimized,and the applicability of the introduction of water vapor in the reaction process and the dehydrogenation of propane and butane was investigated.The results show that for the Fe-W/Al₂O₃ catalyst,the introduction of water vapor in situ can supplement the lattice oxygen to a certain extent and prolong the activity time;compared with the strong cracking activity of the 0.5Li-La_0.6Sr_1.4Fe O₄catalyst for propane and butane,the activity of the Fe-W/Al₂O₃ catalyst is still dominated by dehydrogenation.Combining the two catalyst systems,although the activation time is prolonged due to the increase in the amount of lattice oxygen,the initial activity is still low.