Recovery of phthalic anhydride from still residues

Claim 1

IN THE RECOVERY O FPHTALIC ANHYDRIDE FROM STILL RESIDUES PRODUCED IN DISTILLING CRUDE PHTHALIC ANHYDRIDE, THE IMPROVEMENT WHICH COMPRISES COMMINUTING SOLIDIFED STILL RESIDUE TO PARTICLES OF A SIZE TO PASS THROUGH A STANDARD 1/2-INCH SIEVEM HEATING SAID PARTICLES IN A SOLIDLIQUID EXTRACTION SYSTEM WITH A SOLVENT SELECTED FROM THE CLASS CONSISTING OF LOWER ALKYL KETONES AND LOWER ALKYL ACETATESD, MAINTAINED AT A REFLUX TEMPERATURE BELOW ABOUT 150* C. PHTHALIC ANHYDRIDE BEING SOLUBLE IN SAID SOLVENT AND NONREACTIVE THEREWITH, RECOVERING AN EXTRACT CONTAINING PHTHALIC ANHYDRIDE FROM SAID SYSTEM, DISTILLING THE EXTRACT TO FIRST REMOVE THE SOLVENT THEREFROM, AND DISTILLATE THE EXTRACT RESIDUE TO RECOVER PHTHALIC ANHYDRIDE AS A DISTILLATE THEREFORM.