Abstract: A continuous process for oxidizing a di-alkyl substituted aromatic compound with compressed air in a primary bubble column reactor; including removing a portion of the three phase reaction medium to a post-oxidation bubble column unit supplied with compressed air separating the post oxidation reaction medium to an overhead gas and an underflow slurry; collecting overhead gases from the oxidation reactors and the de-gassing unit and conducting the combined overhead gases to a water removal column (WRC); transferring the underflow slurry from the de-gassing unit to a digestion unit to effect further oxidation without addition of air to the digestion unit; removing overhead gases to the water removal column; crystallizing the final oxidation slurry; and filtering the slurry on a rotary pressure filter; wherein a portion of the energy of the off gas from the WRC is employed to drive an air compressor to supply the compressed air for oxidation.