PREPARATION FOR PHTHALIC ANHYDRIDE OF HIGH PURITY

PURPOSE:To remove impurities efficiently and obtain the titled compound industrially and advantagenously, by bringing crude phthalic anhydride obtained by the catalytic vapor phase oxidation into contact with a gas containing oxygen in the presence of an alkali metallic salt of a carboxylic acid and an alloy composition containing Mn at a high temperature,and distilling the resultant mixture. CONSTITUTION:Crude phthalic anhydride prepared by the catalytic oxidation of o-xylene is treated with a gas containing molecular oxygen in the presence of one or more alkali metallic salts of carboxylic acids, e.g. maleic, succinic and benzoic acids, and an alloy composition containing Mn at a temperature as high as 150-300 deg.C for 0.5-30hr, and the resultant mixture is then distilled to give the aimed compound. Preferably, the gas containing the oxygen is brought into contact with one kg phthalic anhydride at >=1X10mol/hr flow rate expressed in terms of oxygen gas, and the alkali metallic salts are used in an amount of 10-10,000ppm (weight) expressed in terms of metallic atmos. The contact area of the alloy containing Mn is preferably >=1X10m .