Study On The Fe Based Non-noble Metal Catalysts For Acetylene Semi-hydrogenation

The ethylene fraction produced by thermal cracking of petroleum hydrocarbons contains 0.1?2.0 vol%of acetylene,which will lead to the poisoning of subsequent polyolefin catalysts and even the formation of explosive acetylenes.In industry,selective hydrogenation technology is used to remove acetylene,and the catalysts are all noble metal catalysts such as Pd.Noble metal catalysts have high activity but unsatisfactory selectivity and are prone to coking.Coupled with the shortage of resources and high prices,they urgently need to be replaced.Metallic iron is abundant and inexpensive,and the Fe^III-O single active site has been proven to have good acetylene hydrogenation performance,making it a very valuable alternative metal.In this research topic,an iron-based acetylene selective hydrogenation catalyst with excellent performance was developed using the most common commercial alumina as a support and an industrially feasible synthesis method.details as follows:1.Using ferric nitrate as the precursor and calcined spherical alumina at 1000°C as the carrier,the active component iron is loaded by a simple saturated impregnation method.The phase state of iron in the catalyst is adjusted through calcination activation and gas phase reduction process.The research results show that the unreduced oxidized catalyst has no hydrogenation activity,and the catalyst exhibits hydrogenation characteristics after hydrogen reduction,and the reduction temperature has a great influence on the performance of the catalyst.More than 50 sets of cross-variable experiments have determined that the optimal iron loading in the catalyst?-Al₂O₃/Fe O_x is 6%,and the optimal activation and reduction temperatures are 500°C and 450°C,respectively.Under the front-end hydrogenation process conditions,the catalyst?-Al₂O₃/Fe O_x can completely remove acetylene at 135°C,and the ethylene selectivity exceeds 80%.When the raw material also contains C3 fraction,the catalyst can simultaneously catalyze the selective hydrogenation of propyne and propadiene,the total conversion rate of the two is 56.7%,and the selectivity of propylene is 95.2%.After 120h long-term micro-reaction evaluation,there is no coke deposition on the surface of the catalyst,showing excellent anti-coking performance and long-term operation stability,and the overall performance reached the level of industrial Pd Ag catalysts.2.Through TPR,XRD,XPS analysis and characterization,it is clear that the iron oxide species in the catalyst?-Al₂O₃/Fe O_x is a mixed crystal form containing part of ferric oxide,and the ratio of ferrous iron to ferric iron in the optimal catalyst is 1:1.Through the experimental design of hydrogen deuterium exchange,acetylene-TPD and ethylene-TPD,it is found that the optimal catalyst with Fe^III/Fe^II ratio of 1:1 not only has the highest hydrogen activation capacity,but also has high acetylene adsorption capacity and relatively low ethylene adsorption capacity.It is the reason for its acetylene hydrogenation activity and ethylene selectivity.Therefore,it is speculated that during the selective hydrogenation of acetylene,Fe^III and Fe^II in a ratio of 1:1 will combine with hydroxyl groups to form a ring-complexed overall structure(Fe^II---HO===Fe^III).When the reaction occurs,the H on the hydroxyl group in Fe^II---HO===Fe^III will adsorb and activate acetylene,and the adjacent Fe^II and hydroxyl oxygen will interact with hydrogen to dissociate to form active hydrogen.The activated acetylene reacts rapidly with the adjacent active hydrogen to obtain ethylene.Ethylene is desorbed from the catalyst surface due to weak adsorption force,and the intermediate state catalyst also returns to the initial state,and the next catalytic reaction is continued.3.The catalyst was scaled up in kilograms and evaluated in a 750 m L industrial sideline.The evaluation results were basically equivalent to those of the micro-reaction.At 140°C,the acetylene conversion rate was 100%,and the ethylene selectivity was 81.8%.The support research shows that the?-type alumina calcined at about 1000°C has the best catalyst performance among the alumina supports calcined at different temperatures.At this temperature,the spherical and tooth spherical alumina supports have better performance,followed by clover-shaped supports.Pre-calcination at?600°C can effectively improve the strength of alumina carrier.Preparation technology research shows that distributed impregnation is beneficial to catalyst activity and can improve ethylene selectivity by more than 1%,temperature and hydrogen ratio in the reduction process have great influence on catalyst performance and should be strictly controlled.The process condition test shows that the catalyst?-Al₂O₃/Fe O_x is not sensitive to the change of reactor pressure and hydrogen content in the raw material.However,high space velocity and high acetylene content will reduce the acetylene conversion rate of the catalyst,so it is necessary to further increase the reaction temperature to ensure the acetylene in the raw material.of complete removal.In general,the catalyst?-Al₂O₃/Fe O_x is easy to be scaled up and has excellent adaptability to suppport?raw materials and working conditions,showing a good industrialization prospect.4.Based on the research on the iron-based single active component catalyst?-Al₂O₃/Fe O_x,a series of iron-based double non-precious metal catalysts were prepared by introducing the second active component.Among them,after the introduction of zinc oxide,zirconium oxide,and lanthanum oxide,the activity of the catalyst decreased instead.When the acetylene conversion rate was close to 100%,the reaction temperature all exceeded 150°C.However,the introduction of zirconium oxide and lanthanum oxide can improve the ethylene selectivity of the catalyst to more than 85%,which can be used as co-active components in subsequent studies.After the introduction of copper oxide,nickel oxide,and cobalt oxide,the catalyst activity is effectively increased,and the reaction temperature is significantly reduced.Especially for the iron-copper bimetallic catalyst,the acetylene conversion rate is close to 100%at 95°C,and the ethylene selectivity is greater than 75%.Compared with?-Al₂O₃/Fe O_x,the reaction temperature has dropped by 40°C and is already lower than 100°C.Compared with noble metal Pd Ag catalysts,it not only has absolute advantages in terms of price and environmental protection,but also competes in hydrogenation activity.