Study On Synthesis Of P-Aminophenol By Direct Electroreduction Of Nitrobenzene

P-aminophenol , abbreviated as PAP, is an important organic fine chemical and medicine intermediate. It mainly applies to the production of medicines, dyes developing agents and so on. At present the methods of PAP production mainly include:(l) P-nitrophenol powdered iron reduction method;(2) p-nitrophenol catalytic hydrogenation method;(3)nitrobenzene catalytic hydrogenation method;(4) nitrobenzene direct electroreduction method in domestic and abroad. The nitrobenzene electroreduction method has the merits of high product quality (high purity, low iron content), agreement with the drugs manufacture requirements after simple treatment,moreover having no pollutes basically in the technological process, therefore it becomes the present hotspot of R&D in the domestic and abroad. This dissertation studied the electrode process of direct electroreduction nitrobenzene to /j-aminophenol on different electrodes in sulfuric acid systems. The synthetic technology has also been discussed in this dissertation.The main research work of this dissertation is as follows: Based on the chemical reaction engineering theory and the nitrobenzene electroreduction mechanism, the plate and frame electrolyzer was designed and applied to the process of electroreduction nitrobenzene to p-aminophenol. This dissertation measured the residence time distribution data of the electrolyzer by means of the pulse response method and studied the rule of flow pattern along with the current capacity change. Under different conditions ,this dissertation studied the cyclic voltammetry properties of nitrobenzene on different electrodes by means of the dynamic cyclic voltammetry method and the electrode materials applied to the NB electroreduction have been selected primarily.Baseed on the results of cyclic voltammetry tests, this dissertation used p-electrode systems to measure the steady-state- polarization curves of nitrobenzene on different electrodes in H-type diaphragm cell, and obtained each primary factor s influence rule and the exchange current density value of each electrode.And then on the basis of the conclusions of fundamental researchs upword, the effects of influence factors on the the yield of p-aminophenol and the current efficiency,such as electrode material, current density, quantity of electricity circulated, nitrobenzene concentration . sulpuric acid concentration and so on, have been studied in detail in the systems of hign temperature , strong acidity and oxygen-poorthrough a series of electrolysis experiments in this paper.After all using Pb as anode Monel metal as cathode Dupont Nafion 417 cation-exchange membrane as membrane, this dissertation obtained the optimum technological condition: reaction temperature about 85C, current density 500A m-2, sulphuric acid concentration 20%(wt.) , nitrobenzene apparent concentration 6.75% (wt.), quantity of electric charge 95% of theory.Under this condition, the average yield of p-aminophenol and the current efficiency could reach above 70% during the 600 hours continual electrolysis ,which indicated that the electrolyzer structure matched the reaction well and the electrode & diagram materials were stable. Meanwhile during the course of investigation on the stability of Monel metal, its activeness and selectivity droped after 600 hours.In order to disclosure the reason why the electrocatalysis activeness and selectivity droped after being used several hundred hours continuously, the x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscope (EDS) have been used to characterize the surface condition variations of Monel metal. The results indicated: Monel metal belongs to the Cu-Ni alloy around the electrolysis experiment.And after being used for 600hr, the surface layer element composition and geometry distribution of the alloy changed, namely in the alloy the Cu element /which superficial free enthalpy was smaller, "concentrated" to the alloy surface,and formed one kind of marble structure microcrystallite.Thus the electrode surface becamed rough a...