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Study On Catalytic Hydrogenation Of M-Dinitrobenzene And Its Reaction Kinetics Over Nickel-based Catalysts

Posted on:2004-07-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y X LiuFull Text:PDF
GTID:1101360092980625Subject:Industrial Catalysis
Abstract/Summary:PDF Full Text Request
The catalytic hydrogenation technology of m-dinitrobenzene in liquid phase is an attractive and elegant routine for the production of m-phenylenediamine, owing to the advantages such as high product yield, good product quality and much less pollution to environment. Thus, it is practically significant to develop a new catalyst with high catalytic property for m-dinitrobenzene hydrogenation. The supported nickel catalyst has been long-term used for some hydrogenation technologies, due to its lower cost, easy availability, ideal catalytic activity and environmental benefit. Up to now, however, few works about hydrogenation of m-dinitrobenzene over supported nickel catalyst has been reported. In this thesis, the supported nickel catalyst has been attempted to use for the hydrogenation of m-dinitrobenzene in order to find an effective catalyst with high activity, selectivity and long service life.A series of supported nickel-based catalysts for the liquid-phase catalytic hydrogenation of m-dinitrobenzene to m-phenylenediamine have been designed and prepared by the incipient impregnation and the sol-gel methods. The effects of supports, contents of nickel, calcination and reduction temperatures, promoters and preparation methods on the physico-chemical properties of catalysts have been characterized, using the technologies of nitrogen adsorption-desorption (BET), X-ray diffraction (XRD), thermal gravimetry (TG), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), temperature-programmed desorption of hydrogen (H2-TPD), X-ray photoelectron spectra (XPS) and infrared spectroscopy (IR), and the catalytic activities, selectivies and stabilities of the catalysts have been evaluated. Based on the thermodynamic and kinetic analyses for the hydrogenation reaction, the intrinsic kinetic model of Langmuir-Hinshelwood type has been established, and the related kinetic parameters have been evaluated. Finally, A B-P neural network is used to optimize the catalytic reaction conditions.It has been found that among the catalysts prepared by impregnation method, the nickel-based catalyst supported on SiO2 with the nickel content of 20wt% which is calcinated at 773K and reduced at 723K in hydrogen respectively, has showed the best activity and selectivity. Before impregnating nickel, the addition of 3wt% lanthana into Ni/SiO2 could enhance the activity, selectivity and stability of catalyst apparently.Compared with the catalysts prepared by impregnation method, the SiO2 supported nickel catalysts prepared by the sol-gel method have the special properties of higher specific surface area, higher dispersivity of nickel and higher thermal stability. Therefore, they have shown better activity and selectivity for m-dinitrobenzene hydrogenation. The addition of promoter La2O3 into such catalyst has made the performance of catalysts even better.Thermodynamic analysis for the reaction system has shown that the hydrogenation of m-dinitrobenzene to m-phenylenediamine, and the possibleintermediate hydrogenation are all strongly exothermal reactions and can carry through spontaneously. Based on the reaction scheme I, the intrinsic kinetic model of Langmuir-Hinshelwood type can well describe the experimental data, namely the intermediate of m-nitrobenzoic hydroxylamine can not be converted to the end product of m-phenylenediamine, but firstly transform to m-nitroaniline, and then to m-phenylenediamine. The activation energies of the related reactions are 20~36 kJ/mol, and the heat of the intermediates adsorption are -10~-28 kJ/mol. These values agreed well with those reported in literatures.The optimization by the B-P neural network for the reaction has shown the most favorable reaction conditions would be: alcohol is used as solvent, the reaction temperature is 365 K, the pressure is 2.9 MPa, and the catalyst amount is 20%. Under these reaction conditions, the yield of m-phenylenediamine is reached to 95.8%.
Keywords/Search Tags:m-dinitrobenzene, m-phenylenediamine, liquid-phase hydrogenation, supported nickel-based catalyst, incipient impregnation, sol-gel method, reaction kinetics, B-P neural network
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