PRODUCTION OF HIGH-PURITY PHTHALIC ANHYDRIDE

PURPOSE:Crude phthalic anhydride from o-xylene is brought into contact with an oxygen-containing gas at elevated temperature in the presence of alkali metal salt of maleic acid, succinic acid or benzoic acid, then subjected to distillation to give the titled substance free from phthalide. CONSTITUTION:Crude phthalic anhydride containing impurities such as phthalide, which is obtained by the vapor-phase oxidation of o-xylene, is brought into contact with an oxygen-containing gas in the presence of an alkali metal salt of maleic, succinic or benzoic acid at 150-300 deg.C for 0.5-30hr, then subjected to distillation to give high-purity phthalic anhydride. The amount of the alkali metal salt added is 10-10,000, preferably 50-1,000ppm as the alkali metal atom based on the curde product and the oxygen-containing gas is at least 0.001mol/ hr, preferably 0.002-0.01mol/hr per kg of the crude product calculated at oxygen gas.