Process for the purification of crude acetic anhydride

Claim 1

A process for the purification of crude acetic anhydride, which contains at least 89.5% by weight of acetic anhydride, by continuous fractional distillation to obtain substantially pure acetic anhydride having a content of above 98% by weight of acetic anhydride and having a permanganate number of less than 10 and a color number of less than 5, the steps comprising: introducing the crude acetic anhydride into a first evaporator and separating the crude acetic anhydride into vaporous distillable and non-vaporous non-distillable components; thereafter removing the non-distillable components from the first evaporator and from the purification process and then introducing the vaporous distillable components into about the central section of a fractional distillation column and fractionally distilling it therein; withdrawing from the top of the column components having a boiling point below that of acetic anhydride, withdrawing from near the bottom of the column substantially pure acetic anhydride having a content of above 98% by weight of acetic anhydride and having a permanganate number of less than 10 and a color number of less than 5, and removing from the sump of the column a liquid residue consisting substantially of crude acetic anhydride and accumulated impurities having a boiling point higher than that of acetic anhydride; said fractional distillation being the sole fractional distillation of said pure acetic anhydride and returning up to about 8% by weight of the liquid residue to said first evaporator, based upon the initial amount of crude acetic anhydride introduced into the first evaporator.