ABSTRACT
The oldest process for the manufacture of acetic anhydride was based on the conversion of sodium acetate in the presence of an inorganic chloride such as thionyl chloride to give acetyl chloride which is reacted with further sodium acetate to give acetic anhydride. Rapid increases in ethylene and energy costs in the 1970s led Halcon to the development of a new route to acetic anhydride based on methyl alcohol and carbon monoxide via methyl acetate. Most cellulose acetate producers use the liquid pump process to recover acetic anhydride from concentrated waste acids, and this route is gaining in popularity because of its energy efficiency. The dehydrated mixture from the base of the reactor is distilled to recover acetic anhydride. Unreacted carbon monoxide gas from the top of the reactor is cooled to remove any iodides, esters and acetic anhydride before being recycled. Water must be used with caution because acetic anhydride reacts generating much heat.
