Eastman-Halcon process

This process is one of the three commercially practiced processes for the production of acetic anhydride. The other two are the oxidation of acetaldehyde [75-07-0] and the carbonylation of methyl acetate [79-20-9] in the presence of a rhodium catalyst (coal gasification technology, Halcon process) (77). The latter process was put into operation by Tennessee Eastman in 1983. In the United States the total acetic anhydride production has been reported to be in the order of 1000 metric tons. 

Eastman-Halcon A process for making acetic anhydride from syngas. The basic process is the carbonylation of methyl acetate. Methanol is made directly from the carbon monoxide and hydrogen of syngas. Acetic acid is a byproduct of the cellulose acetate manufacture for which the acetic anhydride is needed. The carbonylation is catalyzed by rhodium chloride and chromium hexacarbonyl. 

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]. 

Because acetic anhydride is more useful to the chemical industry than acetic acid, there was economic incentive to develop a process that would yield the anhydride directly without first producing the acid as a separate operation. By the early 1980s, Eastman Chemicals, in conjunction with Halcon Chemical Company, developed a procedure that provided acetic anhydride using technology similar to the Monsanto process, and since 1991 a plant run by Eastman has produced anhydride in excess of 500,000 metric tons per year.89 The Eastman-Halcon (E-H) operation amounts formally to inserting CO into the C-0 bond of methyl acetate according to equation 9.36.90... 

The Eastman acetic anhydride [108-24-7] process provides an extension of carbonylation chemistry to carboxyUc acid esters. The process is based on technology developed independendy in the 1970s by Eastman and Halcon SD. The Eastman acetic anhydride process involves carbonylation of methyl acetate [79-20-9] produced from coal-derived methanol and acetic acid [64-19-7]. 

In many applications acetic acid is used as the anhydride and the synthesis of the latter is therefore equally important. In the 1970 s Halcon (now Eastman) and Hoechst (now Celanese) developed a process for the conversion of methyl acetate and carbon monoxide to acetic anhydride. The process has been on stream since 1983 and with an annual production of several 100,000 tons, together with some 10-20% acetic acid. The reaction is carried out under similar conditions as the Monsanto process, and also uses methyl iodide as the "activator" for the methyl group. 

In the 1970s, Halcon discovered that MeOAc carbonylation to AC2O could be carried out at industrially attractive rates and selectivities by using a Rh catalysed process promoted with Mel and an iodide salt [4], This was developed into a process operated by Eastman [5]. 

Acetic anhydride. Halcon SO developed a process for making acetic anhydride, based on mcllianol 3I. which is being commercialized with Eastman Kodak 32]. The chemistry is shown in Scheme 8. 

Eastman Chemical Company, together with Halcon, developed a commercial acetic anhydride process to an industrial scale [41b, 47]. This process starts with coal to make a hydrogen-rich synthesis gas, which is purified (Figure 4). A portion of the syn gas is separated to produce methanol from 2 1 H2/CO. Part of the methanol is used to scrub H2S from the coal-gasification step. The remainder of the methanol is combined with acetic acid to make methyl acetate. The methyl acetate is carbonylated to give acetic anhydride. The acetic anhydride is used to produce cellulose acetate in another process, and the resulting acetic acid is recycled to the esterification section. The acetic anhydride step of the pro-... 

On the basis of this development afforded by Eastman and Halcon, in 1983 the Eastman Chemical Company (Kingsport, TN) started the commercial process for the manufacture of acetic anhydride (Figure 5). Methyl acetate, the feedstock for the carbonylation reaction, was produced in a separate esterification step from acetic acid and methanol. The process was designed to produce 225 000 tons of acetic anhydride and 75 000 tons of acetic acid/year. The overall yield of acetic anhydride based on methanol is approximately 96 % [2, 47]. 

While the process was commercialized in 1983, Eastman Chemical Company and Halcon began a joint development of the Rh catalyzed carbonylation of methyl acetate to acetic anhydride in the late 1970 s. While the catalyst was similar to the Rh catalyst used in the Monsanto process, there were some unique challenges since (i) under anhydrous conditions the active catalyst, Rh(CO)2l2, failed to form, (ii) unlike water, acetic acid did not react with acetyl... 

Similar intermediates are possibly involved in the Halcon/Eastman route to acetic anhydride from methyl acetate ", and BP Chemicals acetic acid/acetic anhydride co-production process, both now commercialized. However, all these cyclic mechanisms may be incomplete, as individual steps may themselves be complex or catalysed by other species present, and the author has omitted many (minor) side-reactions. 

Frg. 22.20. Acetic anhydride by carbonylation of methyl acetate, Halcon/Eastman process. Chem Systems PERP Report No. 88-7. Copyright Chem Systems, /nc. and used by permission of the copyright owner.)... 

---