Process for the separation of isophthalic and terephthalic diesters

Claim 1

A PROCESS OF SEPARATING MIXTURES OF LOWER ALKYL ALCOHOL DI-ESTERS OF ISOPHTHALIC ACID AND TEREPHTHALIC ACID, WHICH COMPRISES CONTACTING SAID MIXTURES SUCCESSIVELY WITH TWO SOLVENTS HAVING DIFFERENT SOLUBILITY RATIOS FOR THE ISOPHTHALATE OVER THE TEREPHTHALATE, THE MIXTURES BEING FIRST CONTACTED WITH BENZENE IN AN AMOUNT JUST SUFFICIENT TO ENTIRELY DISSOLVE THE MORE HIGHLY SOLUBLE ISOPHTHALATE, WITHDRAWING THE UNDISSOLVED TEREPHTHALATE IN A NEARLY PURE STATE, REMOVING THE BENZENE FROM THE DISSOLVED MIXTURE OF ISOPHTHALATE AND TEREPHTHALATE, THE RESIDUAL MIXTURE THUS OBTAINED BEING THEN CONTACTED WITH A SOLVENT SELECTED FROM THE GROUP CONSISTING OF METHYL ALCOHOL, ETHYL ALCOHOL AND LOW MOLECULAR WEIGHT FATTY ACID ESTERS THEREOF IN AN AMOUNT JUST SUFFICIENT TO ENTIRELY DISSOLVE THE TEREPHTHALATE AND THE UNDISSOLVED EXCESS OF ISOPHTHALATE BEING WITHDRAWN IN A NEARLY PURE STATE, THE FOREGOING ORDER OF SEQUENCE IN CONTACTING THE MIXTURES WITH THE SOLVENTS BEING REVERSED WHEN THE RATIO OF ISOPHTHALATE TO TEREPHTHALATE IN THE STARTING MIXTURE IS GREATER THAN 20 TO 1, REMOVING THE SOLVENT FROM THE DISSOLVED MIXTURE AND RECYCLING THE RESIDUAL MIXTURE THUS OBTAINED TO REPEAT THE FOREGOING STEPS.