Study On Bifunctional Catalyst For Hydrogenation Of Benzene To Cyclohexylbenzene

Cyclohexylbenzene is an important new chemical intermediate,which can be used to produce phenol and co-produce high value-added cyclohexanone.Benzene hydroalkylation to produce cyclohexylbenzene has the advantages of wide raw material sources,simple process,and environmental friedly in the production process.However,the existing catalysts have a catalytic performance gap due to the mismatch between the hydrogenation metal active site and the alkylation acid site There is still a long way to go towards industrial applications,especially the low selectivity of cyclohexylbenzene.In view of the problems of the existing catalysts,this thesis firstly studied the relationship between the matching degree of the metal active sites and acid sites of the catalysts and the catalytic performance of the hydroalkylation of benzene to cyclohexylbenzene.On this basis,the excellent performance,especially a benzene hydroalkylation catalyst with high cyclohexylbenzene selectivity and high catalytic stability was developed,and the kilogram scale-up preparation and molding of the catalyst was successfully achieved.The main results of this thesis are as follows:(1)First,using Hβ zeolite as the support and bimetallic Pd-Ni as the hydrogenation active component,the metal hydrogenation of the catalyst was studied by using different preparation methods,changing the acidity of the H(3 zeolite and adjusting the active metal component and its content.The relationship between the matching of the active site and the alkylated acidic site with the catalytic performance of benzene hydroalkylation to cyclohexylbenzene was investigated.The results show that the preparation method significantly affects the catalytic performance,and the catalyst prepared by the reduction method has the highest selectivity.The main reason for this result is that the reduction method can better retain the framework structure and acid amount of the molecular sieve support,as well as having larger pores.The structure is conducive to the formation and desorption of cyclohexylbenzene;the ratio of SiO2/Al2O3 determines the acidity of the Hβ zeolite support and thus affects the catalytic performance.The Hβ zeolite with a low SiO2/Al2O3 ratio is more suitable for benzene hydrogenation due to more acid sites for the synthesis of cyclohexylbenzene.The introduction of precious metals can improve the hydrogen activation and hydrogenation capacity of the catalyst,thereby greatly improving the activity of the catalyst.Among the catalysts examined,the 0.1Pd-4Ni/Hβ25(SiO2/Al2O3=25)prepared by the reduction method has the best catalytic performance due to the good degree of matching of the metal active sites and acid sites.At a temperature of 150℃,H2 pressure of 2.0 MPa,a mass space velocity of 42 h-1,and a molar ratio of hydrobenzene of 0.33,the conversion rate of benzene is about 19%,and the selectivity of cyclohexylbenzene can reach 80%,but its stability still needs to be further improved.(2)Compared with 0.1Pd-4Ni/Hβ25,the 0.1Pd-4Ni/HY5 catalyst has better catalytic performance because it has more acid sites.Based on this,the 0.1Pd-4Ni/HY5 catalyst was prepared and shaped in kilogram scale.The catalyst life evaluation results show that the 0.1Pd-4Ni/HY5 catalyst prepared by scale-up has excellent catalytic performance,especially selectivity and stability.Under the reaction conditions of temperature 150℃,H2 pressure 2.0 MPa,mass space velocity 42 h-1,and hydrogen benzene molar ratio 0.33,within 1000 h of continuous reaction,the benzene conversion rate is stably kept at the value above 26.3%,and the cyclohexyl selectivity remains above 85%.