Preparation And Properties Of Selecitive Hydrogenation Catalyst For Adiponitrile

The double active functional group of hexamethylene diamine determines that it is an important chemical intermediate.Various downstream products such as nylon,fiber,resin and other polymer materials prepared by condensation reaction are widely used in various fields such as aerospace,minerals,agriculture,etc.At present,China's production capacity of hexamethylene diamine is not enough to match its growing demand.It is the main task to realize industrial large-scale production of hexamethylene diamine at an early date.For the adiponitrile hydrogenation process,the traditional Raney-type catalyst exhibits excellent catalytic activity and has poor mechanical properties.The process requires the addition of alkaline additives,serious pollution and other disadvantages,and the products in many studies are mostly the primary amines coexisting with hexamethylenediamine and 6-aminocapronitrile,which mainly increases the difficulty of subsequent separation.Therefore,several new supported catalysts were designed and applied to the hydrogenation of adiponitrile.In this paper,a series of nickel-based single metal catalysts were prepared by using co-current co-precipitation method and sol-gel method using alumina as the carrier.The production process was optimized,and the difference in the catalytic performance of different preparation methods for the hydrogenation of adiponitrile without alkaline additives was studied and compared.Secondly,a series of nickel-based bimetallic catalysts modified with metal oxides?MO_x=CeO₂,La₂O₃ or MgO?were further prepared,and the effects of different metal additive types,active metals,additive metal content,reaction conditions and other factors on the catalytic performance of Ni-based catalysts in the adiponitrile hydrogenation reaction were also explored.The experimental results show that the introduction of metal additives will produce a synergistic effect between bimetals,promote dispersion to a certain extent,and reduce the particle size of Ni particles.In particular,the introduction of CeO₂ will present sub-nano-cluster dispersed Ni particles,which is conducive to the formation of the Ni-CeO₂ interface to control the electrons and surface structure of the nickel particles,and serves as an electron donor for the active site of Ni,promoting the reduction of nickel metal,instead of changing the crystalline state or H₂ activation energy barrier.It was also found that the yield of hexamethylene diamine increased exponentially with the number of reduced nickel species.After loading CeO₂,the center of the d-band calculated by density functional theory has changed and is close to the Fermi level,this is a reasonable explanation for accelerating the reaction rate.By using a Ni-Ce₃/Al₂O₃catalyst containing only 3 at%CeO₂,adiponitrile can be completely converted for 3hours at 90^oC and 7 MPa H₂ to achieve 100%conversion of adiponitrile and 91%selectivity to hexamethylenediamine.It does not contain 6-aminocapronitrile as a by-product.