Selective heterogeneous catalytic hydrogenation of adiponitrile to 1,6 hexamethylenediamine over precious metal on carbon catalysts

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Previously, at the Department of Organic Chemistry and Technology of BME, a new method for selective liquid-phase heterogeneous catalytic hydrogenation of nitriles to primary amines was developed. Complete conversion, high isolated yield (90%) and selectivity to primary amine (95%) can be obtained in the hydrogenation of benzonitrile under mild reaction conditions (30 C, 6 bar), over a supported palladium catalyst (Pd/C), in a mixture of two immiscible solvents (water/dichloromethane) and in the presence of a medium acidic additive (NaH2PO4). Very pure product (>99% purity) can be achieved without applying any further purification procedures (e.g. distillation). During the course of my MSc-work, I have screened some carbon supported precious metal catalysts (10% Pd/C, 10%Pt/C, 5% Rh/C, 5% Ru/C and 5% Ir/C) and investigated the effects of the catalytic metals, temperature, catalyst/substrate ratio and solvents on the selectivity, isolated yield and the coversion of adiponitrile under the same conditions used in the palladium-catalysed hydrogenations of benzonitrile or benzyl cyanide. Under similar conditions, however, the palladium-catalysed hydrogenation of adiponitrile resulted in complete conversion with lower isolated yield (57%), but neither primary amine (1,6-hexamethylenediamine, HMDA) nor other important intermediate, 6-aminocapronitrile (ACN) was obtained.

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Liquid phase hydrogenation of adiponitrile (ADN) to 6-aminocapronitrile (ACN) and hexamethylenediamine (HMD) was investigated on Ni/SiO2 catalysts prepared under different conditions. In this reaction, the highly reactive imine intermediate forms condensation byproducts by reacting with the primary amine products (ACN and HMD). A highly dispersed Ni/SiO2 catalyst prepared by the direct reduction of Ni(NO3)2/SiO2 was found to suppress the condensation reactions by promoting the hydrogenation of adsorbed imine, and it gave excellent hydrogenation activity and primary amine selectivity. Addition of NaOH increased the primary amine selectivity to 79% at the ADN conversion of 86%.
New production technologies for nylon intermediate chemicals are advancing—slowly—toward commercialization. Researchers at nylon intermediates manufacturers including DuPont, BASF, DSM, Rhodia, and Solutia are developing several new routes to nylon's key raw materials—caprolactam for nylon 6 and the comonomers adipic acid and hexamethylenediamine (HMD) for nylon 6,6. However, the road to commercialization for these technologies has been full of delays, and the conflicting opinions among competitors as well as would-be partners demonstrate that, so far, there are no sure technological winners. In August, DSM announced that it had linked up with Shell Chemicals to develop a new butadiene-based route to caprolactam (C&EN, Aug. 28, page 10). The agreement signaled the end of a research alliance between DSM and DuPont under which the two firms had amassed some 40 joint patents on the new technology. In August, DSM announced that it had linked up with Shell Chemicals to develop a new butadiene-based route to caprolactam (C&EN, Aug. ...
Studies of the chemical preparation, BET surface areas, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature-programmed reduction (TPR) and catalytic activities of several nickel catalysts were carried out for the catalytic hydrogenation of adiponitrile, in a continuous process at 1 atm pressure, 443 K, and in the absence of ammonia. Surface areas decrease with NiO reduction temperature. XRD, XPS and TPR measurements detect NiO incipient reduction at 473-498 K, a NiO reducibility inhibitor character for potassium, and 99.9% reduction degrees above 573 K. Selectivities of 100% with respect to 6-aminohexanenitrile are obtained at 60% conversion for catalysts with potassium contents of 10.5 X 10(-4) g K2O/g Ni.
A series of bimetallic NiCrx and NiMox catalysts were prepared by co-reduction of mixtures of dry iodides of appropriate composition with sodium naphthalene as reducing agent. Observations by transmission electron microscopy (TEM) and local analyses (scanning TEM and energy-dispersive X-ray spectrometry) showed that this procedure gave finely divided homogeneous alloys. The bimetallic powders (50–200Å) developed a large BET surface area (100–170 m2g−1). Auger spectra showed that chromium was strongly segregated on the surface in an oxidized state, whereas molybdenum was metallic and no segregation was observed. The turnover number (TON) of cyclohexene hydrogenation did not depend on the nature of the promoter or on the composition (TON=0.28±0.2 s−1). For acetophenone hydrogenation, NiCrx catalysts exhibited catalytic activity greater than commercial Raney nickel; the initial rate on NiCr0.12 was ten times greater. In addition to their great activity, NiCrx catalysts showed better selectivity, the yield of 1-phenylethanol being as high as 95%. NiMox catalysts were approximately as reactive as commercial Raney nickel, with an increase in the rate of hydrogenolysis of the COH bond.
The Ni–B amorphous alloy in the form of ultrafine particles was prepared by chemical reduction with BH4− in aqueous solution. In comparison with other Ni-based catalysts, such as the ultrafine Ni powder prepared by NH2NH2 reduction and Raney Ni catalyst used commonly in the industrial nitrile hydrogenation, the as-prepared Ni–B catalyst exhibited higher activity and better selectivity to ethylamine during the liquid phase hydrogenation of acetonitrile. Under the present reaction conditions, the maximum yield of ethylamine over the Ni–B amorphous alloy reached 67.6%, much higher than that over Raney Ni (
CONTENTS I. Introduction 319 II. Reaction conditions 319 III. Deamination of primary amines 322 IV. Mechanism of the catalytic reduction of nitriles 322 V. Influence of dinitrile structure on the course of the reaction 326 VI. Influence of the nature of the catalyst on the course of the reaction 327
The activity and selectivity of platinum for the liquid-phase hydrogenation of cinnamaldehyde into cinnamyl alcohol are improved by adding FeCl2 to the reaction medium. Analytical microscopy shows that iron is deposited on Pt-particles. The reaction data are interpreted in terms of a dual-site mechanism.
Carbon nanotube-based catalysts (Pt, Ru, and Pt–Ru) were developed and compared with their analogues on activated carbon for the selective reduction of cinnamaldehyde to the corresponding unsaturated alcohol. The use of a mesoporous nanostructured support, which makes mass transfer limitations less significant, gave far better activities than microporous activated carbon. A bimetallic system was found to afford a remarkably high selectivity (93%) for high conversion levels (80%), provided that a thermal pretreatment was performed on the catalyst. These results can be rationalized in terms of electron transfer from the support to the metal.
The CoB amorphous alloy catalyst was prepared by chemical reduction of Co2+ ions with BH4− in aqueous solution. Its activity and selectivity were measured during the liquid phase hydrogenation of acetonitrile and the effects of various factors, such as the reaction time, acetonitrile concentration, hydrogen pressure, reaction temperature, and solvent, were investigated. The following results were obtained: (1) The maximum ethylamine yield of 69% was obtained at the total conversion of acetonitrile. (2) The acetonitrile hydrogenation was zero-order with respect to acetonitrile and first-order with respect to hydrogen. Meanwhile, the selectivity to ethylamine increased slightly with the increase of either hydrogen pressure or acetonitrile concentration. (3) Increased reaction temperature resulted in a great enhancement in the activity (the apparent activation energy was determined as 46 kJ/mol) but a slight decrease in the selectivity to ethylamine. (4) Addition of a little H2O may result in an increase in the activity. All these effects are discussed based on the reaction mechanism. In comparison with other Co-based catalysts, such as Raney Co, pure Co powder catalyst, and the crystallized CoB catalyst, the amorphous CoB catalyst exhibited much higher activity and better selectivity to ethylamine. Although Ni-based catalysts had higher activity, their poorer selectivity to ethylamine suggested that they were not suitable for the title reaction under the present conditions. Based on the reaction mechanism and various characterizations, including SAED, XRD, SEM, TEM, EXAFS, XPS, hydrogen chemisorption, and DSC, the promoting effects on the activity and selectivity of the CoB amorphous catalyst are discussed briefly by considering both the structural characteristics and the electronic interaction between the Co and the alloying B.
Two Ni–MgO systems were synthesized and characterized as nickel catalysts for the hydrogenation of 1,6-hexanedinitrile (adiponitrile) in the gas phase. The activity results were compared with those obtained for a commercial Raney–Ni. All three catalysts showed high selectivity to 1,6-hexanediamine, for a total conversion with a maximum of 96% for the Ni–MgO catalyst, which was made from a NiO–MgO solution. However, only Ni–MgO catalysts showed high selectivity to 6-aminohexanenitrile (83 and 77%, respectively) and high conversion (87 and 85%, respectively). The higher selectivity to 6-aminohexanenitrile could be related to the presence of octahedral crystallites in the Ni–MgO catalysts.
Layered double hydroxides (LDHs) with a hydrotalcite-like structure and containing Ni2+/Co2+/Mg2+/Al3+ cations in different amounts were prepared and activated in various conditions. Depending on the chemical composition and the calcination temperature, mixed-oxide and spinel-like phases of complex compositions are obtained. They lead to well-dispersed bimetallic phases of high metal loadings upon reduction. Temperature-programmed reduction by H2 showed that the introduction of Mg decreases the reducibility of metals and that most of the Ni and Co are together in bimetallic aggregates. These catalysts were tested in the gas-phase hydrogenation of acetonitrile between 350 and 450 K and with a H2/CH3CN molar ratio of ca. 33. The main product is ethylamine (MEA); secondary products are N-ethyl,ethylimine at low conversion, diethylamine and triethylamine at high conversion. The Ni-free catalyst is three orders of magnitude less active than the Ni-containing samples. The by-products are formed by condensation between “imine-” and “amine-like” adsorbed species on metal and acid sites (bifunctional mechanism) and on the metal sites alone as well. The tuned addition of Mg (Mg/(Mg+Ni+Co)≈0.25) lowers the surface acidity and the bifunctionalized formation of by-products consequently. A net increase in MEA selectivity is further reached thanks to the formation of bimetallic NiCo phases. It is proposed that by-product formation on the metal surface occurs by condensation at Ni0 sites between multibonded adsorbed species, which could be of the acimidoyl and aminomethylcarbene types. The first role of Co is the dilution of the Ni surface in small ensembles less prone to accomodate neighboring multibonded species. The IR spectroscopy of adsorbed CO provided evidences of the dilution of Ni by Co in bimetallic NiCo particles. A catalyst obtained from the Co/Ni/Mg/Al (0.27/0.26/0.22/0.25) LDH, calcined at 393 K and then reduced at 893 K, exhibits the highest selectivity to ethylamine, 98.2% at 10% CH3CN conversion.
The study of the activation energies of reduction of stoichiometric and nonstoichiometric potassium-free and potassium-doped NiO was carried out by means of temperature-programmed reduction experiments, using two compared theoretical methods. Nonstoichiometric NiO shows the lower initial activation energy of reduction, whereas stoichiometric NiO shows a higher initial activation energy for starting the autocatalytic nucleation. Studies of the chemical preparation, BET surface areas, X-ray diffraction, X-ray photoelectron spectra, scanning electron microscopy, and measurements of catalytic activities of the nickel samples for the catalytic hydrogenation of 1,6-hexanedinitrile, in a continuous process at 1 atm pressure and 443 K, in the absence of ammonia, were also carried out. Surface areas decrease when NiO reduction temperatures increase. XRD, XPS, TPR, and SEM measurements detect NiO incipiently reduced between 463 and 498 K, a NiO reducibility inhibitor character for potassium, and 99.9% reduction above 573 K for all NiO forms. 100% selectivities with respect to 6-aminohexanenitrile may be obtained at 60% conversions for catalysts with potassium contents of 10.5 [times] 10[sup [minus]4] g K[sub 2]O/g Ni on reduced nonstoichiometric NiO. A mechanism for the continuous process is proposed. 29 refs., 5 figs., 7 tabs.
Three phase hydrogenation of adiponitrile (ADN) to hexamethylene diamine (HMD) proceeds via aminocapronitrile (ACN). In a first step it has been investigated in selected conditions of temperature, pressure, reagent and catalyst concentrations, avoiding external and intraparticle transfer limitations. Based on initial reaction rates, a Langmuir Hinshelwood model has been selected, involving limiting surface reaction between dissociate hydrogen and nitriles adsorbed on different sites. From concentration profiles different ACN adsorption coefficients depending on ADN concentration have been derived and explained by amine-nitrile interactions. Additional runs performed at lower stirring speeds have then been analysed using the intrinsic kinetic law to estimate the gas-liquid and liquid-solid mass transfer parameters. Comparison with parallel physical measurements performed in the same equipment but without reaction is discussed.
A model for batch heterogeneous reactors is presented in which the unsteady state behaviour of the different kinetic phenomena is considered. The model takes into account the accumulation of reactants in the pores of the catalyst, the accumulation of the adsorbed components on the surface of the pores and the kinetics of adsorption and desorption process. The effects of these factors are analyzed. Finally the model was applied to examine experimental data.
The co-hydrogenation of acetonitrile and butyronitrile over Raney-Co was investigated in order to obtain insight into the mechanism underlying the formation of secondary amines. Acetonitrile was reduced much faster to the corresponding primary amine due to stronger adsorption on the catalyst surface. In parallel, dialkylimines were formed and subsequently converted to secondary amines. It is suggested that the dialkylimines are formed by reaction of partially hydrogenated intermediate species on the cobalt surface with amines. In this respect, n-butylamine was found to react much faster than ethylamine. The stronger inductive effect of the butyl chain is thought to facilitate nucleophilic attack of the amine at the α-C-atom of the surface species. By comparing the C2 and C4 balance for dialkylimines and dialkylamines, it was found that direct hydrogenation of the dialkylimine cannot be the only way of dialkylamine formation. Instead, it is suggested that alkyl group transfer occurs by reaction of a monoalkylamine with a dialkylimine and cross-transfer between two dialkylimines.
This paper deals with the three-phase catalytic hydrogenation kinetics of adiponitrile on Raney nickel. It has been stated that the surface reaction is the limiting step, and that hydrogen is being dissociated at the catalyst surface. The Langmuir-Hinshelwood kinetic formalism seems to be the most appropriate model to fit the experimental data. The major difficulty relative to model discrimination based on the Langmuir-Hinshelwood hypothesis concerns the types of catalytic sites involved: a single site according to competitive adsorption or two catalytic sites corresponding respectively to hydrogen and nitrile. Compared to initial kinetics, complete kinetics provide much more information and this is the main reason why they generate more accurate laws. This accuracy permits significant discrimination between the two models for the catalytic sites, a distinction not achieved by any other means.A complementary analysis of parameter estimation and significance reveals an incomplete determination of the adsorption constants, which can only be optimized through their ratios. Also discussed are other significant effects on the hydrogenation kinetics, such as the role of the solvent and evidence of interactions between species, with a view to future possible Langmuir-Hinshelwood modeling in the liquid phase.
The hydrogenation kinetics of a dinitrile over a Raney-type nickel catalyst was evaluated from experiments performed in a fed-batch operating autoclave at 320– and 2– hydrogen pressure. This complex catalytic reaction consists of two main parts: almost 100% selective hydrogenation of the dinitrile to the corresponding aminonitrile and consecutive hydrogenation to either the desired primary diamine or to pyrrolidine via ring formation. An extensive study has been made on the effects of mass transfer in the applied slurry-type reactor for this reaction. The gas–liquid mass transfer is enhanced by the presence of catalyst particles, and at typical hydrogenation conditions, kLa values up to can be reached. A Sherwood correlation for the three-phase reactor showed that important parameters in the gas–liquid mass transfer are stirrer speed and the density and viscosity of the solvent. The kinetic experiments were performed in absence of mass and heat transfer limitations. The kinetic data were modeled using two rate models based on Langmuir–Hinshelwood kinetics, assuming the reaction of dissociatively adsorbed hydrogen and nitrile compound as rate-limiting step. The first model involved competitive adsorption between hydrogen and organic compound and the second model was based on non-competitive adsorption. Both models successfully described both reaction parts. The reaction of dinitrile to aminonitrile is nearly 100% selective due to the relatively strong adsorption of the dinitriles as compared to the aminonitriles. By increasing the hydrogen partial pressure, higher yields of primary amine can be obtained. The models predict that operating in the mass-transfer regime at relatively high temperatures reduces the formation of the primary diamine.
The influence of LiOH promotion on Co-based Raney-catalysts for the selective hydrogenation of butyronitrile to n-butylamine was explored. Doping with LiOH led to an increase in the fraction of metallic surface area and reduced concentration of Lewis acid sites resulting from alumina particles decorating the metal surface. Two factors were found to be crucial to achieving high selectivity to primary amines. These factors include a low adsorption constant of n-butylamine relative to butyronitrile (because adsorbed butylamine is necessary for byproduct formation) and a low concentration of Lewis acid sites catalyzing condensation reactions.
Amorphous binary (CoB, NiB) and ternary (CoBCr, NiBCr) alloys prepared by chemical reduction with NaBH4 were characterized by atomic absorption spectroscopy (AAS), nitrogen physisorption (BET), X-ray diffraction (XRD), temperature programmed desorption (TPD), temperature programmed reduction (TPR), hydrogen chemisorption, scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS) and the influence of their properties on catalytic performance in the hydrogenation of unsaturated nitriles to unsaturated amines was studied. The hydrogenation over NiB(Cr) catalysts lead to preferential hydrogenation of the CC bond, whereas the hydrogenation over CoB(Cr) catalysts occurred preferentially to the unsaturated amine. Addition of chromium dramatically increased the activity of both NiB and CoB catalysts, due to its effect on the binding energy of adsorbed hydrogen and the adsorption strength of the nitrile functional group. Amorphous cobalt borides treated with sodium hydroxide can hydrogenate unsaturated nitriles to primary unsaturated amines with medium-to-high selectivity without the presence of ammonia.
Glucose hydrogenation has been studied in a well stirred, high-pressure batch reactor on promoted Raney-nickel catalysts. Mo-, Cr-, and Fe-promoted catalysts were prepared by soda attack on Ni40-χAl60Mχ alloys. Sn-promoted catalysts were obtained by controlled surface reaction of Sn(Bu)4 on the hydrogen-covered surface of a Raney-nickel obtained from a Ni2Al3 alloy. The loading of tin is stoichiometric and its distribution on the nickel surface is very homogeneous down to nanometer scale. For an optimum promoter concentration the catalysts are up to seven times more active than unpromoted ones. A good distribution of the promoter in the catalyst grain is required to obtain the best rate enhancement; in the case of molybdenum this is obtained by annealing the alloys. The promoters in a low-valent state on the nickel surface act as Lewis adsorption sites for the oxygen atom of the carbonyl group which is then polarized and thus more easily hydrogenated via a nucleophilic attack on the carbon atom by hydride ions. The activities of Mo- and Cr-promoted catalysts decrease slightly after several recyclings in successive hydrogenation experiments. This is mostly due to surface poisoning by cracking products formed in side reactions. Fe- and Sn-promoted Raney-nickel catalysts deactivate very rapidly because Fe and Sn are leached away from the surface. Iron is washed to the liquid phase whereas tin remains in the Raney-nickel micropores.
This personal account summarizes our recent developments of catalytic hydrosilylations and hydrogenations of carboxylic amides and nitriles to selectively give amines. Special focus is given to highly chemoselective iron- and zinc-catalyzed reductions of amides.
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