Process for the recovery of pure phthalic anhydride from the crude product obtained by the oxidation of o-xylene

摘要

Crude phthalic anhydride, obtained by the oxidation of o-xylene, is purified from maleic acid and water by distilling off 5 to 25% by weight of the crude material at a pressure of 20 to 200 mm. Hg and a still-temperature not exceeding 225 DEG C., and then distilling over pure phthalic anhydride at such a reduced pressure that the still-temperature does not exceed 200 DEG C. A tarry residue, comprising about 2 to 8% by weight of the crude material, remains behind as distillation-residue.