Vapor-phase catalytic hydrogenation, aniline

The non-monotonic functional dependence of kinetic rate expressions is well known in gas-solid catalytic reactions, and was reported in the literature for many other systems. Takahashi et al. (1986) reported the non-monotonic behaviour for the hydrogenation of benzene, Cordova and Gau (1983) for benzene oxidation to maleic anhydride, Yue and Olaofe (1984) for the catalytic dehydrogenation of alcohols over zeolites, and Das and Biswas (1986) for the vapor phase condensation of aniline to diphenylamine. 

The predominant process for manufacture of aniline is the catalytic reduction of nitroben2ene [98-95-3] ixh. hydrogen. The reduction is carried out in the vapor phase (50—55) or Hquid phase (56—60). A fixed-bed reactor is commonly used for the vapor-phase process and the reactor is operated under pressure. A number of catalysts have been cited and include copper, copper on siHca, copper oxide, sulfides of nickel, molybdenum, tungsten, and palladium—vanadium on alumina or Htbium—aluminum spinels. Catalysts cited for the Hquid-phase processes include nickel, copper or cobalt supported on a suitable inert carrier, and palladium or platinum or their mixtures supported on carbon. 

Aniline is an aromatic amine used in the manufacture of dyes, dye intermediates, rubber accelerators, and antioxidants. It has also been used as a solvent, in printing inks, and as an intermediate in the manufacture of pharmaceuticals, photographic developers, plastics, isocyanates, hydroquinones, herbicides, fungicides, and ion-exchange resins. It is produced commercially by catalytic vapor phase hydrogenation of nitrobenzene (Benya and Cornish 1994 HSDB 1996). Production of aniline oil was listed at approximately 1 billion pounds in 1993 (U.S. ITC 1994). Chemical and physical properties are listed in Table 1-2. 

Vapor Phase Hydrogenations of Nitro Compounds. Catalytic hydrogenation of nitro compounds can be carried out in the vapor phase, provided the boiling point of the compound is low enough and the material is thermally stable. These two conditions effectively limit this process to aliphatic and relatively simple aromatic nitro compounds such as nitrobenzene or nitroxylene. Eady vapor-phase hydrogenation processes used fixed-bed catalysts. However, fluidized-bed catalytic vapor-phase hydrogenations, such as the one illustrated by the process for aniline, have become more common (see Amines, aromatic, aniline and derivatives). 

Catalytic hydrogenation requires a catalyst such as nickel, copper, platinum, molybdenum, or tungsten. These catalysts usually are supported on other materials and are especially prepared for the type of reduction to be carried out. Reduction conditions vary widely, depending on the nature of the nitro compound and the catalyst. Reduction may be carried out in solvent in the vapor phase or in the liquid phase. Aniline can be made by continuous vapor-phase reduction of nitrobenzene at 350 to 460°C at nearly atmospheric pressure. Some reductions, on the other hand, are run at 1000 to 4000 psi. 

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