Process for resolving aromatic polycarboxylic acids capable of forming intramolecular anhydrides

Claim 1

A PROCESS FOR RESOLVING A MIXTURE OF AT LEAST TWO AROMATIC POLYCARBOXYLIC ACIDS, EACH OF SAID ACIDS HAVING TWO CARBOXYL GROUPS STERICALLT CAPABLE OF FORMING AN INTRAMOLECULAR ANHYDRIDE AND POSSESSING CHARACTERISTCALLY DIFFERENT DEHYDRATION TEMPERATURES, SAID MIXTURE BEING SELECTED FROM THE COMBINATIONS OF (A) 3-NITR ORTHOPHTHALIC ACID AND 4-NITRO ORTHOPHTHALIC ACID, (B) CHLORO ORTHOPHTHALIC ACIDS AND ORTHOPHTHALIC ACID, (C) METHYL ORTHOPHTHALIC ACIDS AND 3,6-DIMETHYL ORTHOPHTHALIC ACIDS, (D) 4-CARBOXY ORTHOPHTHALIC ACID AND ORTHOPHTHALIC ACID, (E) 4-CARBOXY ORTHOPHTHALIC ACID AND 4-METHYL ORTHOPHTHALIC ACID, AND (F) 4-T-BUTYL ORTHOPHTHALIC ACID AND 4-CARBOXY ORTHOPGTHALIC ACID, WHICH PROCESS COMPRISES HEATING SAID MIXTURE IN THE PRESENCE OF A REFLUXING AROMATIC HYDROCARBON TO A TEMPERATURE INTERMEDIATE OF SAID INDIVIDUAL DEHYDRATION TEMPERATURES FOR A PERIOD OF TIME SUFFICIENT TO DEHYDRATE ONLY ONE OF SAID AROMATIC ACIDS TO THE ANHYDRIDE THEREOF WHILE MINIMIXING DEHYDRATION OF THE OTHER OF SAID AROMATIC ACIDS, THEREBY FORMING A LIQUID FRACTION CONTAINING AROMATIC ACID ANHYDRIDE AND AROMATIC HYDROCARBON AND A SOLID FRACTION COMPRISING AROMATIC POLYCARBOXTLIC ACID, AND THEREAFTER SEPARATING THE TWO FRACTIONS.