Preparation Of The Bifunctional Supported Nickel Based Catalysts And Its Catalytic Performance In Adiponitrile Hydrogenation

?-Caprolactam is one of the most important organic chemical intermediates.It is also the main raw material for the synthesis of nylon-6 fiber,nylon-6 engineering plastics and film.The industrial production routes of ?-caprolactam mainly include cyclohexanone-hydroxylamine route,toluene nitration route and cyclohexane photonitrification route.The traditional production route is mainly cyclohexanone-hydroxylamine route,and the production capacity of ?-caprolactam by this route is more than 95%of the total production capacity.Cyclohexanone is prepared from benzene or phenol by cyclohexanone-hydroxylamine route,and then cyclohexanone oxime is prepared by oximation of cyclohexanone and hydroxylamine,followed by converting to ?-caprolactam through Beckmann rearrangement in the presence of oleum.However,cyclohexanone-hydroxylamine routes have several disadvantages such as multi-step reations,low atom efficiency,high energy consumption,reactor corrosion,environmental pollution and large amounts of ammonium sulphate are formed.In recent years,researchers at home and abroad have paid close attention to the study of the new production process of ?-caprolactam,with emphasis on reducing cost and developing green production process.Hexanediamine is also an important chemical raw material,mainly used in the synthesis of nylon-66 and nylon-610,as well as in the production of nylon resin,polyurethane,plastics,coatings,adhesives,bleach,rubber auxiliaries and so on.Butadiene hydrocyanation/adiponitrile hydrogenation method is new technologies for production ?-caprolactam,which can effectively overcome the above-mentioned problems so as to be one of the main options for green ?-caprolactam production.Adiponitrile hydrogenation is the key step and needs improvement.Hence,we designed and prepared a novel catalytic material with polymetallic synergistic catalytic effect and applied in highly selective hydrogenation of adiponitrile to 6-aminohexanenitrile and 1,6-hexanediamine.The results of this work would also simplify and improve the present technology of?-caprolactam production and is of great scientific value and application prospects.Ni/sepiolite,potassium and(or)lanthanum doped Ni/sepiolite catalysts were prepared by the incipient impregnation method and applied in adiponitrile hydrogenation.It was revealed that the potassium could inhibit the formation of the 1-azacycloheptane by-product by neutralizing some acid sites on the catalyst,and the lanthanum could efficiently reduce the diameter and improve the dispersion of the active nickel particles.It shows that the catalyst doped with potassium and lanthanum gives the best catalytic performance,the selectivity to 6-aminohexanenitrile and 1,6-hexanediamine reaches to 91.3%at 92.5%conversion of adiponitrile under 393 K and 2.0 MPa.Different inorganic acids were used to activate sepiolite,and the acid-activated sepiolites supported nickel and potassium bimetallic catalysts were prepared.The catalytic performance of the acid-activated sepiolite supported K-Ni bimetallic catalysts were investigated in adiponitrile hydrogenation in liquid phase.It was revealed that the potassium could increase the alkalinity of the catalyst with the aim of inhibiting the formation of the 1-azacycloheptane.And the addition of potassium reduces the particle size of nickel and improves its dispersion.Compared with hydrochloric acid and sulfuric acid,nitric acid treatment increases more silanol groups(Si-OH)on the sepiolite surface,which is helpful to nickel particles adsorption and dispersion.Nitric acid activated sepiolite supported nickel and potassium bimetallic catalysts(K-Ni/NASEP)present the best catalytic performance,the conversion of adiponitrile comes up to 92.0%under moderate conditions of lower temperature and pressure,the selectivity to 6-aminocapronitrile and 1,6-hexanediamine is up to 95.2%.Activated carbon supported potassium and iron doped nickel-based catalysts were prepared.The catalytic behaviors were conducted on the hydrogenation of adiponitrile to 6-aminohexanenitrile and 1,6-hexanediamine under 338 K-358 K and 2 MPa hydrogen pressure.It can be deduced that the reducibility of the nickel oxide,the surface of the Ni0+content and the dispersibility of nickel nanoparticles can be significantly enhanced by doping a certain amount of iron as the results of the synergetic effect between nickel and iron.Moreover,the introduction of potassium not only can effectively increase the alkaline site of the catalyst so as to inhibit the formation of by-products,but also improve the dispersion of nickel nanoparticles by suppressing the sintering effect.However,the addition of excessive potassium is unfavorable to the nickel oxide reduction.It can be seen that activated carbon supported potassium and iron doped nickel-based catalyst gives better catalytic performance of 91.3%conversion of adiponitrile and 91.8%selectivity to 6-aminohexanenitrile and 1,6-hexanediamine under mild conditions of 348 K and 2 MPa.Multi-walled carbon nanotubes supported nickel nanoparticles doped with magnesia and copper catalysts were prepared by incipient wetness impregnation method and used in adiponitrile hydrogenation to 6-aminohexanenitrile and 1,6-hexanediamine.The results showed that the introduction of magnesia could lead to form NiO-MgO eutectic so as to restrain the reduction of nickel oxide,and it might increase the alkaline site which is conducive to the formation of primary amines in adiponitrile hydrogenation so as to increase the selectivity to 6-aminohexanenitrile and 1,6-hexanediamine.Moreover,the formation of NiO-MgO eutectic can also inhibit the sintering of nickel in a certain extent,hence promote the nickel dispersion.And it was revealed that doping of copper can highly promote the catalytic activity by attributing to the strong synergetic effect between copper and nickel which can lead to better dispersion of nickel nanoparticles,larger metallic surface area,lower reduction activation energy of nickel oxide precursor and higher ratio of Ni0+on the surface of the support.Multi-walled carbon nanotubes supported nickel nanoparticles doped with copper and magnesia presents the best catalytic performance of 96.3%conversion of adiponitrile and 91.2%selectivity to 6-aminohexanenitrile and 1,6-hexanediamine under 2 MPa and lower temperature of 328 K.Amine-,carboxyl-,hydroxyl-and nitrogen modified multi-walled carbon nanotubes(NH2-MWCNTs,COOH-MWCNTs,OH-MWCNTs and N-MWCNTs-T)supported nickel-based catalysts were prepared by wetness impregnation-reduction method and applied in adiponitrile hydrogenation.It was found that different functional groups such as NH2-,COOH-,OH-on the surface of MWCNTs can effectively act on metal ions by electrostatic attractions and chemical interactions so as to provide nucleation sites,and N species in MWCNTs can act as active sites for Ni deposition due to the strong electronic interactions between N species and Ni so as to promote ultra-small Ni nanoparticles formation,decrease the reduction activation energy of NiO,increase the amounts of zero-valent Ni as well as the Ni nanoparticles dispersion.Furthermore,the doped N on MWCNTs increases the lewis basicity,which favors the formation of primary amine of 6-aminohexanenitrile and 1,6-hexanediamine.Moreover,the basic ionic liquid[Bmim]OH may switch the selectivity by inhibiting nucleophilic addition of the primary amine to the?-carbon of aldimine via the stabilization of-NH2 groups in the amino-imine intermediates so as to impede by-products formation.In addition,the mechanism for adiponitrile hydrogenation in[Bmim]OH was studied by density functional theory calculations.Under optimized conditions,the selectivity to 6-aminohexanenitrile is up to 81.8%at 90.2%adiponitrile conversion or the selectivity to 1,6-hexanediamine is up to 90.4%at 100%adiponitrile conversion,especially it gives 97.8%total selectivity to 6-aminohexanenitrile and 1,6-hexanediamine at 95.3%adiponitrile conversion over Ni/N-MWCNTs-800 in the presence of[Bmim]OH.