Acetic anhydride, manufacture

Acetic acid, trimethylenediaminetetra-metal complexes equilibrium constants, 2, 784 synthesis, 2,779 Acetic anhydride manufacture, 6,330... 

FIGURE 4 Acetic anhydride manufacture by carbonylation of from methyl acetate. 

Thermodynamically, the carbonylation of methyl acetate (AG298 -10 kJ/mol) is considerably less favourable than that of methanol (AG298 -74 kJ/mol). This means that the reaction does not reach completion but attains an equilibrium which is dependent on the temperature and the CO pressure. Two variants are currently practised commercially that developed by Tennessee Eastman, based on a Halcon process, and a BP process in which acetic acid and the anhydride are co-produced in proportions which can be varied according to demand. Syngas for the Eastman process is made from coal which is mined close to the plant in Tennessee and the acetic anhydride produced is used to make cellulose acetate for film production. The BP process uses syngas generated from North Sea gas which is piped directly to the BP plant in EIull. [Acetic anhydride manufacture M. J. Eloward, M. D. Jones, M. S. Roberts, S. A. Taylor, Catalysis Today, 1993, 18, 325]. 

Jeffreys, in a treatment of the design of an acetic anhydride manufacturing facility, states that one of the key steps is the vapor-phase cracking of acetone to ketene and methane ... 

Acetic anhydride manufacture from acetone and acetic acid... 

There were also improvements in acetaldehyde and acetic anhydride manufacture. Ag based catalysts for the partial oxidation of ethanol became available around 1940. When used to oxidatively dehydrogenate ethanol [14], the conversion of ethanol to acetaldehyde was no longer equilibrium limited since the reaction was now very exothermic. Fortunately, the process still displayed excellent selectivity (ca. 93-97%) for acetaldehyde. This technology replaced the older Cu-Cr processes over the period of the 1940-1950 and made ethanol a much more attractive resource for acetaldehyde. When ethylene became available as a feedstock in the 1940 s through 1950 s, ethanol became cheaply available via ethylene hydration (as opposed to traditional fermentation). With ethanol now cheaply available from ethylene, the advent of the Ag catalyzed oxidative dehydration to acetaldehyde rapidly accelerated the shutdown of the last remaining wood distillation units. 

Subsequent developments of Eastman carbonylation technology are yet to be commercialized production routes to acetaldehyde, propionic acid, propionic anhydride, methacrylates, and acrylates (29). It is also relevant to note that dimethyl ether, readily available from methanol by dehydration, has recently achieved some prominence as a suitable raw material in carbonylation technology, via the intermediacy of methyl acetate and acetic anhydride in the case of acetic anhydride manufacture. It also offers the advantage of processing under totally anhydrous conditions. 

One of the main uses of acetic anhydride is in the manufacture of cellulose acetate. Cellulose acetate is used in the production of plastics, coating chemicals, etc. Eastman Chemical Company has operated a highly successful rhodium-based acetic anhydride manufacturing process, based on the carbonylation of methyl acetate, for over 25 years. 

---