Production of terephthalic acid with excellent optical properties through the use of pure or nearly pure oxygen as the oxidant in p-xylene oxidation

A process for making an aromatic carboxylic acid, said process comprising the steps of:

• a) providing a body of liquid contained within a reactor vessel, said body of liquid comprising an organic solvent, at least one catalyst selected from the group consisting of manganese and cobalt, and a bromine initiator;
• b) maintaining said body of liquid in a recirculating flow pattern by impeller means positioned therein;
• c) injecting an aromatic alkyl reactant directly into said recirculating portion of the body of liquid at a reactant injection point or points of highest turbulence within a turbulent flow field produced by said impeller means so as to rapidly disperse the reactant into said body of liquid;
• d) injecting pure or nearly pure oxygen into said body of liquid at a point of highest shear which is directly adjacent to, and produced by said impeller means, so as to rapidly disperse oxygen in the liquid as small bubbles for rapid consumption upon injection into the liquid;
• e) maintaining the oxygen-aromatic alkyl mixture in the reactor vessel at a pressure of 90-300 psig, and a temperature between 170.degree. C. and 190.degree. C., for a residence time of about 60 minutes;
• f) recovering aromatic carboxylic acid product having essentially no colored impurities directly from the reactor,
• wherein the aromatic alkyl is p-xylene, the aromatic carboxylic acid is terephthalic acid, and the reactor is a liquid oxygen reactor.

A process for making a terephthalic acid having an optical density, as measured at 340 nm, of less than or equal to 1.28, said process comprising the steps of:

• a) providing a body of liquid contained within a reactor vessel, said body of liquid comprising an organic solvent, at least one catalyst selected from the group consisting of manganese and cobalt, and a bromine initiator;
• b) maintaining said body of liquid in a recirculating flow pattern by impeller means positioned therein;
• c) injecting an p-xylene reactant directly into said recirculating portion of the body of liquid at a reactant injection point or points of highest turbulence within a turbulent flow field produced by said impeller means so as to rapidly disperse the reactant into said body of liquid;
• d) injecting pure or nearly pure oxygen into said body of liquid at a point of highest shear which is directly adjacent to, and produced by said impeller means, so as to rapidly disperse oxygen in the liquid as small bubbles for rapid consumption upon injection into the liquid;
• e) maintaining the oxygen and p-xylene mixture in the reactor vessel at a pressure of 90-300 psig, and a temperature between 170.degree. C. and 190.degree. C., for a residence time of about 60 minutes;
• f) recovering terephthalic acid product having an optical density, as measured at 340 nm, of less than or equal to 1.28 directly from the reactor.