A process for preparing phthalic anhydride by gas-phase oxidation of
xylene, naphthalene or mixtures thereof over two different fixed-bed
catalysts arranged in zones in a shell-and-tube reactor which is
thermostated by means of a heat transfer medium is carried out so that the
maximum temperature in the second catalyst zone in the flow direction is
at least 52.degree. C. lower than the maximum temperature in the first
catalyst zone.
The process of the present invention makes it possible to prepare phthalic
anhydride in high yields under conditions relevant to industrial practice.
