Study Of Preparation Of PAP By Hydrogenation Of Nitrobenzene On Bi-Functional Catalyst Of Pt

p-Aminophenol (PAP)is an important intermediate for the manufacture of analgesic and antipyretic drugs as paracetamol, dyestuff as sulfur dyes, mordant dyes and acid dyes et al. It also can be used as an additive to oil products, a catalyst for production of vinylcyanide, and an anti-ageing agent in rubber industry. In addition, it is also applied to the manufacture of developer, antioxidant. The hydrogenation of nitrobenzene, which operated in the presence of supported noble metal catalyst, aqueous acid medium and surfactant, was more competitive in many preparation technics of PAP. During the reaction, nitrobenzene was hydrogenated to β-phenyl hydroxylamine (PHA) and then rearranged to p-Aminophenol in aqueous acid medium. English HartingChemicals Co. and America Mallin Chrodt Co. had adopted this method to produce PAP. Beijing Medical University, Tianjin University and the Changchun Applied Chemistry Academe of Chinese Academy of Sciencer et al. had made lots of efforts on the investigation of the technics. However by now there is no report on successful industrial application on this technics in China. This technics had many advantages, such as the cheapness and easily availability of raw materials, low production cost and working procedure simplicity. The classical catalyst applied in the reaction was Pd or Pt supported on active carbon. The reaction was under the conditions of 70～110℃ and 0～1MPa with the presence of aqueous acid medium and surfactant. After the reaction, the catalysts suspendded in the left nitrobenzene and PAP could be received from water phase. But the disadvantages of traditional technics were obvious: the catalytic performance was not excellent, aqueous acid medium need acid-resistant equipment and in the other hand, the existence of the surfactant could do harm to procedure control and product purification. As to the aforementioned problems, two solutions were considered. One was to modify active carbon with diverse metal oxide through impregnation and calcinations, then to deposit Pt on the carbon. As a result, the selectivity of PAP was increased.The other solution was the application of a novel catalyst: Bi-functional catalyst. The catalyst was prepared with solid acid as carrier containing acid active sites which lead to the immediate rearrangement of the intermediate, ?-phenylhydroxylamine, to PAP at the surface of the catalyst, where the product PAP desorbed. The selectivity of PAP was improved because the migration distance of the intermediate, β-phenylhydroxylamine, was shortened. The catalysts were prepared and applied in the reaction of hydrogenation-rearrangement of nitrobenzene to PAP. The results showed that the selectivity of PAP was increased and the concentration of sulfuric acid was reduced greatly. In the mean while, the technics was simplified and adapted to industrial application without surfactant.In a word, this technics had some outstanding advantages for industrial application, such as low cost, small pollution emission and the reasonable energy consumption. Furthermore, a considerable enhance of the selectivity of PAP, as a result of the application of this promising Bi-functional catalyst, was achieved.