Eastman chemical company acetic anhydride process

To the casual observer, the rhodium catalyzed carbonylation of methyl acetate would appear to be very similar to the well studied Rh catalyzed carbonylation of methanol. However, several significant differences manifest themselves upon switching from the well documented aqueous methanol carbonylation to the anhydrous methyl acetate carbonylation to acetic anhydride. These include fundamental operational changes imposed by the less favorable thermodynamics, significant changes in the by-products, and significant changes in the nature and operation of the catalyst system which, in addition to Rh and iodine, also requires the presence of both a salt and a reducing agent. The differences between the methanol carbonylation and the methyl acetate carbonylation can be explained via a mechanistic study which, based primarily upon high pressure kinetic and infrared data, leads to a unique mechanistic proposal. The key technical breakthroughs, how they led to a successful commercial process, and comparisons of the methyl acetate carbonylation to the methanol carbonylation will be discussed in detail. A brief historical development of the process is included.