PRETREATMENT PROCESS FOR THE DISTILLATION OF CRUDE PHTHALIC ANHYDRIDE

摘要

Crude liquid phthalic anhydride produced from the catalytic air oxidation of o-xylene, and containing minor quantities of acids such as phthalic acid and in addition, compounds more volatile than phthalic anhydride, is subjected to a special pretreatment to remove the acids and the more volatile materials, said pretreatment having a relatively short residence time and comprising heating said crude liquid phthalic anhydride under a first pressure in the liquid phase to a temperature of about 235 DEG -330 DEG C for a sufficient time to convert said phthalic acid to phthalic anhydride and then expanding said heated liquid to a lower pressure than said first pressure to volatilize gases containing at least a portion of said more volatile substances and simultaneously cool resultant liquid to a temperature lower than the boiling point of phthalic anhydride at said lower pressure.