| abstract |
1. IN A PROCESS OF PURIFICATION OF TEREPHTHALIC ACID (TA) CONTAINING P-FORMYLBENZOIC AND P-TOLUIC ACIDS AS MAIN IMPURITIES AND LESSER AMOUNTS OF COLOR-BODY IMPURITIES, OTHER HEAVY END BY-PRODUCTS, AND MULTIFUNCTIONAL IMPURITIES BY THE CATALYTIC HYDROGENATION AT A TEMPERATURE IN THE RANGE FROM 225 TO 300*C. OF A SOLUTION SUBSTANTIALLY SATURATED WITH SUCH IMPURE TA AT SAID TEMPERATURE IN A LIQUID PHASE OF SOLVENT COMPRISING WATER OR ACETIC ACID CONTAINING 0 TO 45 WEIGHT PERCENT WATER, COOLING THE RESULTING SOLUTION CONTAINING P-TOLUIC ACID AS THE MAIN IMPURITY IN QUANTITY TO CRYSTALLIZE TA AT A TEMPERATURE IN THE RANGE OF 50-165*C. AND SEPARATING CRYSTALLINE TA FROM MOTHER LIQUOR; THE IMPROVEMENT COMPRISING CRYSTALLIZING TA BY COOLING THE SOLUTION THROUGH FLASH EVAPORATION OF A PORTION OF SOLVENT FROM THE TEMPERATURE RANGE OF 225 TO 300*C. DOWN TO A LOWER TEMPERATURE HAVING 180* C. AS THE MINIMUM TEMPERATURE AND A LOWER PRESSURE SUFFICIENT TO MAINTAIN REMAINING SOLVENT IN THE LIQUID PHASE AT SUCH LOWER TEMPERATURE; SUBJECTING THE SUSPENSION OF CRYSTALLINE TA IN REMAINING SOLVENT TO A CLASSIFICATIONLIQUID DISPLACEMENT SYSTEM OPERATED AT SUCH LOWER TEMPERATURE WHEREIN A SUBSTANTIAL PORTION OF THE REMAINING LIQUID SOLVENT SOLUTION OF P-TOLUIC ACID AND OTHER UNDESIRABLE IMPURITIES ARE REMOVED AND A CONCENTRATED CRYSTALLINE TA SUSPENSION IS DILUTED WITH FRESH SOLVENT AT SUCH LOWER TEMPERATURE AND RECONCENTRATED AS A MEANS FOR DISPLACING SUBSTANTIALLY ALL REMAINING ORIGINAL SOLVENT SOLUTION OF P-TOLUIC ACID AND OTHER UNDESIRABLE IMPURITIES, AND FORMING A NEW SUSPENSION OF CRYSTALLINE TA IN HOT FRESH SOLVENT; DEPRESSURIZING AND QUENCHING SAID NEW SUSPENSION OF CRYSTALLINE TA BY THE ADDITION THERETO OF COLD FRESH SOLVENT IN AN AMOUNT TO DEPRESSURIZE TO ATMOSPHERIC PRESSURE AND COOL DOWN TO AT LEAST THE BOILING POINT OF THE FRESH SOLVENT AT ATMOSPHERIC PRESSURE, AND SEPARATING CRYSTALLINE TA FROM FRESH SOLVENT AT ATMOSPHERIC PRESSURE. |