Continuous system for oxidizing substituted aromatic hydrocarbons and producing carboxylic acids

Claim 1

IN A PROCESS FOR PRODUCING AROMATIC POLYCARBOXYLIC ACIDS BY OXIDIZING POLYALKYL AROMATIC HYDROCARBONS CONTAINING 1 TO 3 CARBON ATOMS IN ALKYL GROUPS WITH MOLECULAR OXYGEN IN THE PRESENCE OF A CATALYST COMPRISING IN CONJOINT PRESENCE BROMINE AND A HEAVY METAL OXIDATION CATALYST AND IN THE PRESENCE OF A LIQUID PHASE OF SATURATED MONOCARBOXYLIC ACID CONTAINING 2 TO 5 CARBON ATOMS PER MOLECULE AT A TEMPERATURE IN THE RANGE OF FROM 320 TO 440*F., A PRESSURE IN THE RANGE OF FROM 50 TO 500 P.S.I. FOR A TIME OF FROM 0.1 TO 3 HOURS, THE IMPROVED METHOD OF OPERATION WHICH COMPRISES EFFECTING SAID OXIDATION IN A CONTINUOUS STAGED COUNTERCURRENT REACTION SYSTEM CONTAINING AT LEAST TWO OXIDATION ZONE STAGES, INTRODUCING AN AMOUNT OF AIR IN THE FINAL OXIDATION ZONE STAGE IN AN AMOUNT PROVIDING AN EXCESS OF OXYGEN FOR OXIDATION IN SAID FINAL OXIDATION ZONE STAGE BUT LESS THAN REQUIRED TO GIVE OFF-GASES CONTAINING MORE THAN 8 VOLUME PERCENT OXYGEN, AND INTRODUCING OXYGEN-CONTAINING OFF-GASES FROM SAID FINAL OXIDATION ZONE STAGE TO A PRECEDING OXIDATION ZONE STAGE TOGETHER WITH AN AMOUNT OF AIR WHICH WILL GIVE LESS THAN 8 VOLUME PERCENT OXYGEN IN THE OFF-GASES FROM SAID PRECEDING STAGE.