Recovery of phthalic anhydride from still residue

Claim 1

IN A PROCESS OF CATALYTIC OXIDATION OF NAPHTHALENE TO PHTHALIC ANHYDRIDE, THE RECOVERY OF PHTHALIC ANHYDRIDE COMPRISING: DISTILLING PHTHALIC ANHYDRIDE OXIDATION PRODUCT OF NAPHTHALENE TO TAKE PHTHALIC ANHYDRIDE OVERHEAD, HEATING STILL RESIDUE FROM THE FOREGOING DISTILLATION WITH A SATURATED MONOHYDROXY ALCOHOL OF MOLECULAR WEIGHT LESS THAN 140, TO FORM THE PHTHALIC ACID ESTER OF THE ALCOHOL USED, FILTERING UNREACTED SOLID FROM THE REACTION MIXTURE, DISTILLING THE OAINED FILTRATE AT A TEMPERATURE LESS THAN 110*C. TO DECOMPOSE THE SAID ESTER, REMOVING THE REGENERATED ALCOHOL BY DISTILLATION, SEPARATING REGENERATED PHTHALIC ANHYDRIDE AND RECYCLING RECOVERED ALCOHOL TO THE TREATMENT OF FURTHER QUANTITIES OF STILL RESIDUE.