Abstract: Provided is a process for producing pyromellitic dianhydride by feeding 1,2,4,5-tetraalkylbenzene to a fixed bed multitubular type reactor charged with a catalyst layer to carry out catalytic vapor phase oxidation. This process is characterized by dividing the catalyst layer into at least two layers to charge a layer at an outlet side of reaction gas and a layer at an inlet side of raw material mixed gas with the following catalyst A and catalyst B respectively or dividing the catalyst layer into at least three layers to charge a layer at an outlet side of reaction gas, an intermediate layer and a layer at an inlet side of raw material mixed gas with the following catalyst A, catalyst B and catalyst C respectively:catalyst A: a catalyst containing V.sub.a (A).sub.b P.sub.c Ag.sub.d (B).sub.e O.sub.

Abstract: A method for producing efficiently on a commercial scale pyromellitic anhydride having high purity and suffering only sparing coloration in a high yield from a raw material of high concentration is provided. By the use of a multilayer catalyst formed by packing on the reaction gas outlet side a first catalyst containing V and Mo and/or W and having an atomic ratio of Mo and/or W to V in the range of from 0.01 to 2, on the raw material mixed gas inlet side a second catalyst containing V, Mo and/or W and having an atomic ratio of Mo and/or W to V smaller than the atomic ratio of the first catalyst, and/or a third catalyst containing V and an alkali metal and having an atomic ratio of the alkali metal to V in the range of from 0.2 to 2.5, pyromellitic anhydride is produced by the vapor-phase oxidation of a tetraalkyl benzene with a molecular oxygen-containing gas.