Two different approaches have been used for manufacturing acetic anhydride. One process is a modified oxidation; the other involves ketene as an intermediate. The ketene is usually obtained from the dehydration of , and then reacted with acetic acid. Alternatively, ketene can be manufactured from acetone.

The modified acetaldehyde oxidation with air or O₂ was developed by Hoechst-Knapsack. A variation was developed by Shawinigan, in which a mixture of Cu and Co acetate was used as catalyst instead of Mn acetate. The reaction is run in the liquid phase at 50 °C and 3-4 bar.

The primary acetyl radical is formed from acetaldehyde by abstraction of hydrogen. This is oxidized by Cu to the acetyl cation, which reacts with acetic acid to form acetic anhydride:

In a parallel reaction, peracetic acid is formed by addition of O₂ to the acetyl radical with subsequent abstraction of hydrogen from acetaldehyde. The acid serves to reoxidize Cu⁺ to Cu²⁺:



Acetic acid formed from this acetoxy radical is, therefore, an inevitable coproduct.

The water formed can now initiate the secondary reaction of acetic anhydride to acetic acid if it is not quickly removed from the equilibrium by distillation with an entraining agent such as ethyl acetate. With 95% conversion of acetaldehyde an optimal ratio (56:44) of anhydride to acid is attained.

In the acetic anhydride manufacturing process involving the dehydration of acetic acid via ketene (Wacker process), acetic acid is first thermally dissociated into ketene and H₂O. The reaction takes place in the presence of triethyl phosphate at 700 - 750 °C and reduced pressure:

To freeze the equilibrium, the resulting H₃PO₄ is neutralized with NH₃ or pyridine while still in the gas phase, and the cracked gas is quickly cooled.

The higher boiling components (acetic anhydride, acetic acid, and water) are separated from the gaseous ketene in a system of graduated coolers. After removing the water, they are recycled to the cracking stage. The conversion of acetic acid is about 80%. The ketene selectivity exceeds 90% (based on CH₃COOH) at an acetic acid conversion of 70-90%. The ketene purified in this way is fed directly into acetic acid (e. g., in the Wacker process, in a liquid-seal pump), and converted at 45-55 °C and reduced pressures of 0.05-0.2 bar into acetic anhydride:

In this stage, selectivity approaches 100%. This acetic anhydride process has the advantage that ketene can be obtained on demand as an intermediary product. Furthermore, acetic acid from the most economical process can be used, including acetic acid from acetylation reactions with acetic anhydride.

New routes for the manufacture of acetic anhydride are the homogeneously catalyzed carbonylation of and methyl acetate as developed by Hoechst and Halcon, respectively. Starting from methanol or its further carbonylation to acetic acid, both processes are based fundamentally on synthesis gas, and thus also on coal, as a feedstock. The carbonylation of methyl acetate has been developed further industrially, and is preferably run at 150- 220 °C and 25-75 bar in the presence of a rhodium salt catalyst system with promoters such as chromium hexacarbonyl/picoline:

In 1983, Tennessee Eastman started operation of a unit in the USA using the Halcon technology, which has since been expanded from its original capacity of 230000 tonnes per year to 300000 tonnes per year.