Because the content of anthraquinone and its homologues and other components in crude phthalic anhydride is very small, no material calculation has been carried out in the reaction section, and the boiling point is very different from that of phthalic anhydride, which is easy to remove and has little impact on the product. Moreover, impurities in crude phthalic anhydride can be basically removed after distillation in a light component tower, which can meet the design requirements.Therefore, the heavy component tower in the phthalic anhydride distillation section is only introduced and not calculated in this design.In this chapter, when material balance is carried out for the phthalic anhydride distillation section, it can be approximated that the phthalic anhydride melt extracted from the bottom of the light component tower is the product phthalic anhydride (i.e. logistics 3).Similarly, only light component columns are considered in the design calculation section of rectification column in this design.