Recovery of phthalic and maleic anhydrides

Claim 1

IN THE PROCESS OF RECOVERING PHTHALIC ANHYDRIDE FROM MIXTURES THEREOF CONTAINING MALEIC ANHYDRIDE AND PHTHALIDE PRODUCED BY CATALYTIC OXIDATION OF ORTHO-XYLENE WHEREIN SAID MIXTURES IN GASEOUS STATE ARE CONTACT WITH A LEAN DIBUTYL PHTHALATE SOLUTION TO FORM A RICH SOLUTION, MALEIC ANHYDRIDE IS STRIPPED FROM THE RICH SOLUTION AND PHTHALIDE IS SUBSEQUENTLY STRIPPED FROM THE SOLUTION, AFTER REMOVAL OF PHTHALIC ANHYDRIDE, TO FORM A LEAN SOLUTION FOR RECYCLE TO THE CONTACTING STEP, THE IMPROVED METHOD OF OPERATION WHICH COMPRISES COOLING DIBUTYL PHTHALATE SOLUTION WHICH IS RICH IN PHTHALIC ANHYDRIDE AND PHTHALIDE TO A TEMPERATURE EFFECTIVE FOR CRYSTALLIZING SUBSTANTIALLY PURE PHTHALIC ANHYDRIDE WHILE RETAINING THE PHTHALIDE IN MOTHER LIQUOR AND SEPARATING PHTHALIC ANHYDRIDE IN CRYSTAL FORM FROM SAID MOTHER LIQUOR.