ABSTRACT
The hydrogenation of nitrobenzene to para-aminophenol (PAP) takes place by way of an initial partial hydrogenation to phenylhydroxyl amine which then undergoes an in situ acid catalyzed rearrangement to PAP. This reaction is most commonly run over Pt/Carbon catalysts in the presence of aqueous sulfuric acid and surfactant to assist in dispersing the nitrobenzene throughout the reaction medium. The yield of PAP is closely related to those reaction parameters which facilitate, first, the partial hydrogenation step and, second, the acid promoted rearrangement before further hydrogenation to aniline can take place. We examined a number of reaction parameters such as hydrogen pressure, temperature, nitrobenzene concentration and the amount of surfactant present in the reaction mixture. High selectivity to PAP formation (>88%) and catalyst productivity (>220 g PAP / g catalyst / hr) at 100% conversion were achieved at a hydrogen pressure of 50 psig and 90°C.
