Liquid phthalic anhydride recovery process using a rectification tower with benzoic acid control

摘要

A process for recovering phthalic anhydride as a liquid from a vapor phase oxidation product which comprises mixing the vapor phase oxidation product having a temperature of about 130 DEG C. or greater with a first stream comprising maleic anhydride, benzoic acid present in an amount of less than 8 mole %, based on the total concentration of the first stream, and at least one compound selected from the group consisting of: citraconic anhydride and phthalic anhydride, in a rectification tower such that a substantial portion of the phthalic anhydride contained within the vapor phase oxidation product transfers from the vapor phase to a liquid phase and a substantial portion of the by-products contained in the first stream which are more volatile than phthalic anhydride transfer from the liquid phase to the vapor phase and wherein a vapor-to-liquid weight ratio in the range between about 2 to 20 is exhibited within the rectification tower, thereby forming a liquid phase phthalic anhydride product having a phthalic anhydride concentration in the range between about 50-100 wt. %.