Acetic Anhydride

Acetic anhydride is produced from glacial acetic acid via ketene (CAS no 463-51-4). Acetic acid is vaporized and fed together with a catalyst to a cracking furnace operating under vacuum where ketene is produced together with water at high temperature. The reaction mixture is rapidly cooled to avoid the reversing of the reaction. The condensed dilute acetic acid is separated and the gases then pass through two absorption towers in which they are scrubbed by acetic acid/ acetic anhydride of various concentrations.
Glacial acetic acid is added to the second absorption tower. Ketene is reacting with acetic acid to form acetic anhydride. In following washing towers the gases are further scrubbed before released to the atmosphere. In a distillation column the crude acetic anhydride is distilled and recovered as the bottom product. The top product is acetic acid which is recycled to the process. Acetic Anhydride is raw material for cellulose acetate (fibres, films, plastics, cellulose lacquers), aspirin, agricultural chemicals, fragrances, pharmaceuticals and explosives.