Preparation Of P-Aminophenol By Electrochemically Reducing Of Nitrobenzene

P-Aminophenol (PAP), a fine chemical material and medicines intermediate, is widely used in medicine, rubber, dye and sensitive material. The PAP used in medicine must be with high purity, which could be prepared through electrochemical reduction of Nitrobenzene.Phenylhydroxylamine (PHA) is generated as an intermediate when Nitrobenzene is electrochemically reduced. Acids can ismomerise PHA to PAP by the Bamberger rearrangement, which determine the selectivity towards PAP. Some acids are studied to increase the selectivity of PAP. PHA is prepared by the Nitrobenzene reduction using zinc powder:the temperature is 62℃-66℃, the reaction time is 60 min, and maximum yield is 74.49%. In aqueous solution, resin has a high catalytical effect. It has been found that the preferred embodiment in acid at 80 "C are as follows:the concentration of H+is 0.5mol/L-2 mol/L, reaction time is 15 min, the most effective acid is phosphoric acid. Cyclic voltammetry is used to study the catalytic effect of several catalysts, which suggests that kieselguhr, sulphated zirconia and beta zeolite have high catalytic activity. P-Chloroaniline (PCA) is produced in the existence of HC1, and when Cl-concentration is 0.3mol/L, PAP selectivity is over 80%.Attempt to release Cl2 on cathode for prolonging the anode lifetime, HC1 and H2SO4 are used as cathode electrolyte and anode electrolyte respectively, separated by cation exchange membrance. The Cl- diffusion behavior is studied as follows:Cl" concentration was rised from 0 to 0.14mol/L after 10h when 5% HC1 is added on the other side of CMV membrance at 60℃and the static Cl-diffusion coefficient through CMV membrane is 1.54×10-6cm2/s at 60℃, while the diffusion coefficient in CMV is 10-7cm2/s. PCA and AN can firstly precipitate together from the solution by controlling the pH=4.5, and then PAP can separate out by adjusting pH= 6.5. AN can be purified by reduced pressure distillation, the purity is over 98%.The recycling of sulfuric acid by diffusion dialysis is studied. The acid recovery efficiency with APS, AHT and AAV membranes are investigated. When the flow rate is 0.003ml/min, the acid recovery efficiency with APS, is up to 68%, which is better than AHT and AAV. PAP and AN could be intercepted by membrances, the penetration rate of PAP and AN is only 1.1% and 0.96%, respectively.