The invention discloses a method for preparing 4-aminodiphenylamine, which comprises the following steps: (1) mixing
aniline and an alkali water solution, and distilling out
aniline-water
azeotrope; (2) adding
nitrobenzene to react; (3) adding water and a hydrogenation catalyst, and introducing
hydrogen gas; (4) carrying out
solid-liquid separation to separate the hydrogenation catalyst and a
liquid phase, returning the hydrogenation catalyst to the step (3) or returning the hydrogenation catalyst to the step (3) after regeneration, separating the
liquid phase to obtain an organic phase and an alkali water solution, rectifying the organic phase to obtain 4-aminodiphenylamine and
aniline, and returning the aniline to the step (1); and (5) returning the alkali water solution to the step (1) or returning the alkali water solution to the step (1) after the alkali water solution is treated by
activated carbon. In the method disclosed by the invention, the
activated carbon is used for treating the circulating alkali water solution so as to remove impurities, thereby improving the purity of the circulating alkali water solution and avoiding the use of an expensive
electrolytic process. Thus, the invention has the advantages of short process
route and low equipment investment, is simple to operate, lowers the
operating cost and reduces the environmental
pollution.