Process for the recovery of terephthalic acid from solutions containing alkali metal salts of terephthalic acid

Claim 1

IN A CYCLIC PROCESS OF PRODUCING TEREPHTHALIC ACID FROM REACTION PRODUCTS OBTAINED BY SUBJECTING A NEUTRAL ALKALI METAL SALT OF A BENZENE CARBOXYLIC ACID OTHER THAN TEREPHTHALIC ACID TO A REARRANGEMENT REACTION AT TEMPERATURES ABOVE 340*C., SAID REACTION PRODUCTS COMPRISING SUBSTANTIAL QUANTITIES OF A DIALKALI METAL TEREPHTHALATE, THE IMPROVEMENT WHICH COMPRISES (STEP 1) DISSOLVING THE DIALKLI METAL TEREPHTHALATE CONTAINED IN THE REACTION PRODUCT IN AN INERT SOLVENT MEDIUM SELECTED FROM THE GROUP CONSISTING OF WATER, WATER-MISCIBLE ORGANIC SOLVENTS AND MIXTURES THEREOF, (STEP 2) REACTING THE DISSOLVED DIALKALI METAL TEREPHTHALATE WITH AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF BENZENE CARBOXYLIC ACIDS OTHER THAN TEREPHTHALATE ACID AND THEIR ACID ALKALI METAL SALTS TO FORM THE CORRESPONDING RELATIVELY INSOLUBLE MONOALKLI METAL TEREPHTHALATE AND A SOLUTION OF THE CORRESPONDING SOLUBLE NEUTRAL ALKALI METAL SALT OF SAID BENZENE CARBOXYLIC ACID, (STEP 3) REACTING THE MONOALKALI METAL TEREPHTHALATE FROM STEP 2 WITH A BENZENE CARBOXYLIC ACID OTHER THAN TEREPHTHALIC ACID IN THE PRESENCE OF AN INERT SOLVENT MEDIUM SELECTED FROM THE GROUP CONSISTING OF WATER, WATER-MISCIBLE ORGANIC SOLVENTS AND MIXTURES THEREOF, TO FORM INSOLUBLE TEREPHTHALIC ACID AND A SOLUTION OF THE CORRESPONDING SOLUBLE ACID ALKALI METAL SALT OF SAID BENZENE CARBOXYLIC ACID, SEPARATING THE TEREPHTHALIC ACID FROM THE SOLUTION OBTAINED IN STEP 3, RECYCLING THE ACID ALKALI METAL SALT OF THE BENZENE CARBOXYLIC ACID FROM STEP 3 INTO STEP 2, AND RECYCLING THE NEUTRAL ALKALI METAL SALT OF THE BENZENE CARBOXYLIC ACID FROM STEP 2 INTO THE THERMAL REARRANGEMENT REACTION TO FORM ADDITIONAL REACTION PRODUCT COMPRISING SUBSTANTIAL QUANTITIES OF DIALKALI METAL TEREPHTHALATE.