Nitro is the classical fcedstock for manufacture. Recently less chlorobenzene and are being used in aniline manufacturing processes in scvcral countries.

The reduction of nitrobenzcne with iron turnings and water in the presence of small amounts of hydrochloric acid is the oldest form of industrial anilinc manufacture. It would certainly have been replaced much earlier by more economical reduction methods if it had not been possible to obtain valuable iron oxide pigments from the resulting iron oxide sludge. However, the increasing demand for aniline has far surpassed the market for the pigments, so that not only catalytic hydrogenation processes (both liquid- and gas-phase) but also other feedstocks have been used for aniline production.

The modern catalytic gas-phase hydrogenation processes for nitrobenzene can be carried out using a fixed-bed or a fluidized-bed reactor:

Rayer and Allied work with nickel sulfide catalysts at 300-475 °C in a fixed bed. The activation of the hydrogenation catalysts with Cu or Cr, and the use of different supports and catalyst sulfidization methods with sulfate, H₂S or CS₂ all belong to the expertise of the corresponding firms. The seleetivity to aniline is more than 99%. The catalytic activity slowly decreases due to carbon deposition. However, the catalyst can be regenerated with air at 250-350°C and subsequent H2 treatment. Similar processes are operated by Lonza with Cu on pumice, by ICI with Cu, Mn, or Fe catalysts with various modifications involving other metals, and by Sumitomo with a Cu-Cr system.

The gas-phase hydrogenation of nitrobenzene with a fluidized-bed catalyst is used in processes from BASF, Cyanamid and Lonza. The BASF catalyst consists of Cu, Cr, Ba, and Zn oxides on a SiO₂ support; the Cyanamid catalyst consists of Cu/SiO₂. The hydrogenation is conducted at 270-290 °C and 1-5 bar in the presence of a large excess of hydrogen (H₂:nitrobenzene=ca. 9:1). The high heat of reaction is removed by a cooling system which is built into the fluidized bed. The selectivity to aniline is 99.5%; the nitrobenzene conversion is quantitative. The catalyst must be regenerated with air periodically.

An alternate manufacturing route for aniline is the ammonolysis of chlorobenrene or of phenol. For example, in the Kanto Electrochemical Co. process, chlorobenzene is ammonolyred to aniline with aqueous NH₃ at 180-220 °C and 60-75 bar in the presence of CuCl and NH₃Cl ("Niewland catalyst"):



Aniline can be isolated with 91 % selectivity from the organic phase of the two-phase reaction product.

Dow stopped operation of a similar process for aniline in 1966. Phenol can also be subjected to gas-phase ammonolysis with the Halcon/Scientific Design process at 200 bar and 425 °C:

Al₂O₃^.SiO₂ (possible as zeolites) and oxide mixtures of Mg, B, Al, and Ti are used as catalysts; these can be combined with additional cocatalysts such as Ce,V, or W. The catalyst regeneration required previously is not necessary with the newly developed catalyst. With a large excess of NH₃, the selectivity to aniline is 87-90% at a phenol conversion of 98%. The byproducts are diphenylamine and carbazole. This process has been operated since 1970 by Mitsui Petrochemical in a plant which has since been expanded to 45 000 tonnes per year. A second plant with a capacity of 90000 tonnes per year was started up by US Steel Corp. (now Aristech) in 1982.

In 1977, Mitsui Petrochemical started production of m-toluidine by the reaction of m-cresol with ammonia in a 2000 tonne-per-year plant, analogous to the phenol ammonolysis. Thus, there is another manufacturing path besides the conventional route (nitration of toluene and hydrogenation of m-nitrotoluene).

Du Pont has developed an interesting new manufacturing process for aniline. Benzene and ammonia can be reacted over a NiO/Ni catalyst containing promoters including zirconium oxide at 350°C and 300 bar to give a 97% selectivity to aniline with a benzene conversion of 13%:

Since the hydrogen formed in the reaction reduces the NiO part of the catalyst, a catalyst regeneration (partial oxidation) is necessary. Despite inexpensive feedstocks, industrial implementation is still thwarted by the low benzene conversion and the necessary catalyst reoxidation.