GB573468A - Improvements in or relating to the manufacture of acetic anhydride - Google Patents

Abstract

Acetic anhydride is produced by oxidation with molecular oxygen of a mixture of acetaldehyde and paraldehyde at below 60 DEG C. followed by distillation in which the water is entrained by the paraldehyde. The initial mixture may be obtained by partial polymerization of acetaldehyde or partial depolymerization of paraldehyde. Suitable depolymerizing agents are sulphuric, phosphoric and sulphonic acids and acidic salts such as zinc, aluminium and ferric chlorides and vanadic acid. The oxidation catalyst should be of such nature and quantity as not to neutralize the depolymerization agent; for instance, manganese or cobalt acetate should be used in small quantity; vanadic acid, especially when activated with acetic acid, may be used with or without cobalt or manganese acetates. An active vanadic catalyst may be made by adding hydrogen peroxide or another peroxidic compound to vanadium pentoxide in acetic acid, whereby the pentoxide is dissolved. Suitable apparatus is described. Examples describe the oxidation with oxygen of (1) paraldehyde, acetaldehyde, and vanadic acid; (2) paraldehyde, sulphuric acid and vanadic acid; (3) paraldehyde, acetic acid, sulphuric acid, cobalt acetate and copper acetate. In each case the water is removed with paraldehyde by azeotropic distillation. The concentration of percompounds in the reaction product can be reduced by diluting with paraldehyde or by adding manganese acetate, preferably after neutralizing any acid depolymerizing agent present. Specification 461,808 is referred to.