Reaction SMILES: BrBr.O.[C:4]([OH:18])(=[O:17])[C:5]1[C:6](=[CH:10][C:11](=[CH:15][CH:16]=1)[C:12]([OH:14])=[O:13])[C:7]([OH:9])=O>C(O)(=O)C.[Zr].[Mn].[Co]>[CH:15]1[C:11]([C:12]([OH:14])=[O:13])=[CH:10][C:6]2[C:7]([O:18][C:4](=[O:17])[C:5]=2[CH:16]=1)=[O:9]
Reactant: O=C(O)c1ccc(C(=O)O)c(C(=O)O)c1
Agent: [Co]
Agent: [Mn]
Agent: [Zr]
Solvent: O
Solvent: CC(=O)O
Product: O=C(O)c1ccc2c(c1)C(=O)OC2=O

Procedure:
We have discovered an improved process for the manufacture of trimellitic acid anhydride by the steps of catalytic oxidation of pseudocumene in the presence of acetic acid in an oxidation zone wherein liquid-phase conditions are maintained and wherein the weight ratio of acetic acid to pseudocumene is in the range of about 0.5:1.0 to about 5.0:1.0 and the catalyst comprises one or more heavy metal oxidation catalysts comprising zirconium, cobalt, and manganese to provide about 0.1 to about 0.4, preferably about 0.22 to about 0.32, weight percent total metals based on pseudocumene and a source of bromine and to provide a total of about 0.10 to about 0.30 weight percent total bromine based on pseudocumene, wherein the total weight ratio of bromine ions to total metal ions is about 0.5 to about 2.0, the zirconium content is about 1 to about 5%, preferably about 2.0 to about 4.0, and the manganese content is about 14 to about 60%, each metal by weight of the total metals and wherein the cobalt content is about 35 to about 80 weight percent, temperatures in the oxidation are in a range of about 220° F. to about 480° F., preferably about 300° F. to about 430° F., cooling the oxidation reaction effluent to crystallize trimellitic acid, separating and recovering crystallized trimellitic acid from the acetic acid solvent mother liquor, distilling from the acetic acid mother liquor to obtain a mixture of acetic acid and water for concentration of the acetic acid content to provide acetic acid solvent concentrate for recycle to the oxidation and to obtain a bottoms fraction having high melting solids, heating the crystalline trimellitic acid to convert it to its anhydride and distilling the anhydride to obtain trimellitic acid anhydride product. The improvement arises from conducting the thermal conversion of the trimellitic acid to its anhydride continuously in two series staged dehydration zones with heat removal by evaporation from the liquid in each of the dehydration zones. The first dehydration zone is operated at a temperature in the range of about 400° to about 500° F., preferably about 420° to about 480° F., and at a pressure in the range of about 10 to about 25 pounds per square inch absolute and the second dehydration zone is operated at a temperature in the range of about 400° to about 500° F., preferably about 420° to about 490° F., and a pressure in the range of about 50 to about 400 mm. Hg thereby converting trimellitic acid to its anhydride and evaporating acetic acid solvent and hydrocarbon. The crude trimellitic anhydride is purified by distillation at a temperature in the range of about 425° to about 575° F., preferably about 450° to about 550° F., and an absolute pressure of about 4 to about 400 mm. Hg, preferably about 4 to about 300 mm. Hg, and condensing the vaporized overhead fraction to obtain trimellitic anhydride product. In the present novel integrated proces for commercial production of trimellitic anhydride the vapor from the first dehydration zone and the acetic acid mother liquor are combined as feed for distilling acetic acid and water mixture therefrom leaving a residue having high melting solids. The residue is combined with the bottom fraction from the distillation of the trimellitic anhydride having catalyst metals and the combined material added to the first dehydration zone in an amount of up to about 50 weight percent, preferably about 10 to 45 weight percent, of the combined residue and bottom fraction.