Study On Ni-based Catalysts And Reaction Conditions For Synthesis Of M-Phenylenediamine By Catalytic Hydrogenation

The catalytic hydrogenation technology of m-Dinitrobenzene in liquid phase is anattractive and elegant routine for the production of m-Phenylenediamine, owing to itsadvantages such as high product yield, good product quality and less pollution toenvironment. Thus, it is practically significant to develop a new catalyst with highcatalytic performance for m-Dinitrobenzene hydrogenation.Supported nickel catalysts have been widely used for some hydrogenationtechnologies, due to their lower cost, easy availability, ideal catalytic reactivity andenvironmental benefit. Up to now, however, few works about hydrogenation ofm-Dinitrobenzene over the supported nickel catalysts have been reported. In thisthesis, the supported nickel catalysts have been used for the hydrogenation ofm-Dinitrobenzene in order to develop a catalyst with high activity, selectivity andlong service life.A series of supported nickel-based catalysts for the liquid-phase catalytichydrogenation of m-Dinitrobenzene to m-Phenylenediamine were designed andprepared by the incipient impregnation method, and their physico-chemical propertieswere characterized by means of nitrogen adsorption-desorption, X-ray diffraction,thermal gravimetry, differential thermal analysis, transmission electron microscopy,scanning electron microscopy, temperature-programmed reduction, infraredspectroscopy and pores size distribution. The catalytic performance of the catalystswas evaluated in autoclave reactor and trickle-bed reactor. Meanwhile, the effects ofthe reaction conditions on the catalytic performance of the catalysts were investigated.The reaction stability and the reasons for deactivation of the catalyst were alsostudied.Compared with the catalysts prepared by multi-step impregnation method, thecatalyst, Cat3, which was prepared by co-impregnation method with a solution ofnickel nitrate, lanthanum nitrate and potassium nitrate, showed better reactivity. Withethanol as solvent, under the conditions: reaction temperature, 373K;H2 pressure,3.0MPa;reduction time of the catalyst, 90 min;catalyst/m-Dinitrobenzene, 3wt.%;solvent / m-Dinitrobenzene, 2/1(wt./ wt.), conversion of m-Dinitrobenzene andselectivity of m-Phenylenediamine for Cat.3 in autoclave reactor were 99.9% andover 99.6% respectively after reaction for about 7 hours;moreover, it showed nodistinct deactivation after use for 20 times, i.e., it had very good catalyticperformance.Ni-La/SiO2 showed good catalytic performance for the hydrogenationperformance of m-Dinitrobenzene in trickle-bed reactor. With ethanol as solvent,under the conditions of 3.0MPa, 353K, GHSV 1000h-1, LHSV 0.22h-1, reduction timeof the catalyst 90 min, conversion of m-Dinitrobenzene and selectivity ofm-Phenylenediamine were over 98% and 99% respectively after reaction for about 3hours. This study provides an important information for the development of thetrickle-bed reactor.In this study, the reason of the deactivation for the catalysts in hydrogenation wasanalyzed. It was found that some organics deposited in the catalyst surface, whichresulted in the decrease of specific surface area, pore volume so as to the surfaceactive area of Ni, and this was the main reason for the deactivation of the catalyst.The oxidation with air then reduction with hydrogenation was the feasible methodfor the regeneration of the deactivated catalyst.