Method for producing monomethyl terephthalate

Claim 1

METHOD FOR PRODUCING HIGH-PURITY MONOMTHYL TEREPHTHALATE SUITABLE DIRECTLY AS A STARTINF PRODUCT FOR THE PRODUCTION OF POLYESTER FIBERS, COMPRISING THE FOLLOWING PROCESS STEPS: A. OXIDIZING P-XYLENE TO P-TOLUIC ACID BY REACTING SAID PXYLENE WITH AN OXYGEN CONTAINING GAS IN A GAS-LIQUID CONTACT SYSTEM AT A TEMPERATURE BETWEEN 90* AND 130*C, A PRESSURE BETWEEN 3 AND 15 ATMOSPHERES, IN THE PRESENCE OF A POLYVALENT HEAVY METAL SALT AS THE OXIDATION CATALYST, AND FOR A TIME SUCH THAT THE CONVERSION OF SAID P-XYLENE TO SAID P-TOLUIC ACID IS BETWEEN 15 AND 60 PERCENT; B. REACTING THE P-TOLUIC ACID FROM STEP (A) WITH METHANOL IN A FIRST ESTERIFICATION STAGE AT A TEMPERATURE BETWEEN 150* AND 230*C AND A PRESSURE BETWEEN 15 AND 60 ATMOSPHERES AND THEN REACTING THE RESIDUAL P-TOLUIC ACID SUBSTANTIALLY COMPLETELY TO P-TOLUIC ACID METHYL ESTER BY COUNTERCURRENT CONTACT WITH GASEOUS METHANOL AT TEMPERATURES BETWEEN 220* AND 260*C AND PRESSURES AT WHICH SAID METHANOL IS SUBSTANTIALLY IN VAPOR FORM; C. OXIDIZING P-TOLUIC ACID METHYL ESTER FROM STEP (B) WITH AN OXYGEN CONTAINING GAS IN A GAS-LIWUID SYSTEM AT A TEMPERATURE BETWEEN 140* AND 170*C, PRESSURES FROM 1 UP TO 6 ATMOSPHERES, IN THE PRESENCE OF A POLYVALENT HEAVY METAL SALT AS THE OXIDATION CATALYST, AND FOR A TIME SUCH THAT BETWEEN 20 AND 45 PERCENT OF SAID METHYL ESTER IS CONVERTED TO MONOMETHYL TEREPHTHALATE; D. SEPARATING THE CRYSTALLINE MONOMETHYL TEREPHTHALATE REACTION PRODUCT FROM THE REACTION MIXTURE FOLLOWING STEP (C); E. DISSOLVING SAID MONOMETHYL TEREPHTHALATE IN A SOLVENT WHICH EXHIBITS A STRONG TEMPERATURE DEPENDENCE FOR THE SOLUBILITY OF MONOMETHYL TEREPHTHALATE, AND CONTACTING THE RESULTING SOLUTION WHICH ACTIVATED CARBON TO REMOVE COLOR IMPURITIES THEREFROM; F. COOLING THE THUS-TREATED SOLUTION TO RECRYSTALLIZE THE MONOMETHYL TEREPHTHALATE THEREFROM; AND G. RECOVERING THE RESULTING HIGH-PURITY MONOMETHYL TEREPHTHALATE PRODUCT.