Abstract: A process for the manufacture of phthalic anhydride by oxidation in the gas phase of an o-xylol naphthalene mixture. By producing a solution of 1 to 80 parts by mass naphthalene in 99 to 20 parts by mass o-xylol at a temperature of 0.degree. to 80.degree. C., storing the solution at that temperature, heating the solution only shortly prior to the reaction to 110.degree. to 180.degree. C., atomizing the heated solution into a hot airflow, passing the heated solution over metal oxide catalysts in the gas phase and collecting phthalic anhydride product, a problem-free manufacture of phthalic anhydride is attained.

Abstract: A method for utilizing distillation residues of phthalic anhydride or maleic anhydride, which comprises: (a) cooling hot, liquid distillation residues of said phthalic anhydride or maleic anhydride while flowing as a stream in a first organic liquid; (b) comminuting said distillation residues solidifying in said first organic liquid by means of a cutting edge rotating at high rpm to produce a granulate; (c) suspending said granulate in a second organic liquid; and (d) incinerating the suspension or converting the suspension into synthesis gas.