Patent ID: 7348452

Claim:
A process for the oxidation of p-xylene to terephthalic acid comprising oxidizing in the liquid phase a p-xylene composition comprising at least 80 wt. % p-xylene based on the weight of liquid reactants, at a temperature in the range of 120° C. to 250° C. and in the presence of a solvent, a source of molecular oxygen and a catalyst composition comprising less than 5 ppm of zirconium atoms, a source of nickel (Ni) atoms, a source of manganese (Mn) atoms, and a source of bromine (Br) atoms, to form a crude reaction mixture comprising terephthalic acid and incompletely oxidized reaction composition comprising 4-carboxybenzaldehyde (4-CBA) compounds, wherein the stoichiometric molar ratio of bromine atoms to manganese atoms is 1.5 or less, and the amount of nickel atoms is at least 500 ppm.