Patent ID: 7608733

Claim:
A process for producing terephthalic acid, said process comprising: oxidizing in a steady state operation para-xylene in a liquid phase of a reaction medium contained within a reaction zone of a bubble column reactor, wherein less than 0.03 volume percent of said reaction medium has a para-xylene concentration greater than 25,000 ppmw on a time-averaged basis, wherein said oxidizing is carried out in a manner such that when said reaction medium is theoretically partitioned into 30 horizontal slices of equal volume, a pX-max horizontal slice has the maximum para-xylene concentration of all of said 30 horizontal slices and a pX-min horizontal slice has the minimum para-xylene concentration of all the horizontal slices located above said pX-max horizontal slice, wherein said para-xylene concentration is measured in a liquid phase of said reaction medium on a time-averaged and volume-averaged weight basis, wherein the ratio of the para-xylene concentration of said pX-max horizontal slice to the para-xylene concentration of said pX-min horizontal slice is at least 5:1.