Acetic acid, Monsanto process

Outline the catalytic processes involved in the manufacture of acetic acid (Monsanto process) and acetic anhydride (Tennessee-Eastman process). 

Scheme 30 Proposed catalytic cycle for methanol carbonylation to acetic acid (Monsanto process). Acyl-iodide reductive elimination from a Rh(ni) center is the key step toward the product formation...

Such iodide effect has been observed in Rh-catalyzed carbonylation of methanol to acetic acid (Monsanto process), where iodide is invoked to hicilitate several key steps. See Maitlis, P.M., Haynes, A, James, B.R., Catellani, M, and Chiusoli, G.P. (2004) Dalton Trans., 3409. 

In the second one, methyltetrahydrofolate (MeTHF) is carbonylated, the product being a thioester, acetyl coenzyme A (CoA being a thiol). This reaction resembles methanol carbonylation to acetic acid (Monsanto process, see Chap. 18) ... 

Monsanto acetic acid A process for making acetic acid by carbonylation of methanol, catalyzed by rhodium iodide. Operated by BP. 

In the late 1960s, workers at Monsanto began studies into the carbonyla-tion of methanol to acetic acid. The process they developed (9-11), now known worldwide as the Monsanto acetic acid process, is based on an iodide-promoted rhodium catalyst system. Because of the high efficiency and selectivity of the reaction (typical commercial operating conditions are 150-200°C and 30-100 atm, giving selectivities >99% based on CH3OH),... 

Monsanto acetic acid A process for making acetic acid by carbonylation of methanol, catalyzed by rhodium iodide. Operated by BP. A variation of this process, the low water process, used added Group 1 metal iodides such as lithium iodide to enhance the productivity this was practiced by Celenese and by Daicel. 

The basic organometallic reaction cycle for the Rh/I catalyzed carbonylation of methyl acetate is the same as for methanol carbonylation. However some differences arise due to the absence of water in the anhydrous process. As described in Section 4.2.4, the Monsanto acetic acid process employs quite high water concentrations to maintain catalyst stability and activity, since at low water levels the catalyst tends to convert into an inactive Rh(III) form. An alternative strategy, employed in anhydrous methyl acetate carbonylation, is to use iodide salts as promoters/stabilizers. The Eastman process uses a substantial concentration of lithium iodide, whereas a quaternary ammonium iodide is used by BP in their combined acetic acid/anhydride process. The iodide salt is thought to aid catalysis by acting as an alternative source of iodide (in addition to HI) for activation of the methyl acetate substrate (Equation 17) ... 

All known ACS enzymes are bifunctional in that they possess a C cluster with COdFI activity in addition to an A cluster (the ACS active site. Scheme 9). In the enzymes, a CO tunnel is described through which GO can pass directly from the C cluster, where it is generated from CO2, to the A cluster, where acetyl GoA synthesis takes place. Again, two mechanisms were proposed that differ in the order of binding events and redox states involved. In essence, however, GO binds to an Ni-GHs species, followed by insertion and generation of an Ni-acetyl species, which upon reaction with GoA liberates the acetyl GoA product. It is interesting to note that methylation of Ni occurs by reaction with methyl cobalamin (Scheme 7). In M. thermoacetica, the cobalamin is the cofactor for a rather unique protein called the corrinoid iron sulfur protein (GFeSP). The above process, even if mechanistic details still remain in question, resembles the industrial Monsanto acetic acid synthesis process (Scheme 9, bottom). In this case, however, the reaction is catalyzed by a low-valent Rh catalyst. 

Roth and co-workers [84] at the Monsanto company developed an acetic acid production process by the reaction of methyl alcohol with carbon monoxide in the presence of rhodium carbonyl as the major catalyst. 

Fig. 25.9 The two interrelated catalytic cycles in the Monsanto (M = Rh) and Cativa (M = Ir) acetic acid manufacturing processes.

In the BASF process, methanol and CO are converted in the liquid phase by a homogeneous Co-based catalyst. The reaction takes place in a high-pressure Hastelloy reactor. In recent decades the BASF process has been increasingly replaced by low-pressure alternatives mainly due to lower investment and operating costs. In the low-pressure Monsanto process methanol and CO react continuously in liquid phase in the presence of a Rhl2 catalyst. In 1996, BP developed a new attractive catalyst based on iridium (Cativa process) the oxidative addition of methyl iodide to iridium is 150-times faster than to rhodium. The search for acetic acid production processes with even lower raw material costs has led to attempts to produce acetic acid by ethane oxidation. In the near future ethane oxidation will most likely not compete with methanol carbonylation (even though ethane is a very cheap and attractive raw material) because of the low ethane conversions, product inhibition problems, and a large variety of by-products. 

Acetic Acid and Anhydride. Synthesis of acetic acid by carbonylation of methanol is another important homogeneous catalytic reaction. The Monsanto acetic acid process developed in the late 1960s is the best known variant of the process. 

This reaction is rapidly replacing the former ethylene-based acetaldehyde oxidation route to acetic acid. The Monsanto process employs rhodium and methyl iodide, but soluble cobalt and iridium catalysts also have been found to be effective in the presence of iodide promoters. 

Ca.ta.lysis, The readily accessible +1 and +3 oxidation states of rhodium make it a useful catalyst. There are several reviews of the catalytic properties of rhodium available (130—132). Rhodium-catalyzed methanol carbonylation (Monsanto process) accounted for 81% of worldwide acetic acid by 1988 (133). The Monsanto acetic acid process is carried out at 175°0 and 1.5 MPa (200 psi). Rhodium is introduced as RhCl3 but is likely reduced in a water... 

This process may be competitive with butane oxidation (see Hydrocarbon oxidation) which produces a spectmm of products (138), but neither process is competitive with the process from synthesis gas practiced by Monsanto (139) and BASF (140) which have been used in 90% of the new acetic acid capacity added since 1975. 

Acetic acid from methanol by the Monsanto process, CH3OH -1-CO CH3COOH, rhodium iodide catalyst, 3 atm (44 psi), 150°C (302°F), 99 percent selectivity of methanol. 

Figure 5-7. The Monsanto methanol carbonylation process for producing acetic acid. ...

The carbonylation of methanol was developed by Monsanto in the late 1960s. It is a large-scale operation employing a rhodium/iodide catalyst converting methanol and carbon monoxide into acetic acid. An older method involves the same carbonylation reaction carried out with a cobalt catalyst (see Section 9.3.2.4). For many years the Monsanto process has been the most attractive route for the preparation of acetic acid, but in recent years the iridium-based CATIVA process, developed by BP, has come on stream (see Section 9.3.2) ... 

Meanwhile, Wacker Chemie developed the palladium-copper-catalyzed oxidative hydration of ethylene to acetaldehyde. In 1965 BASF described a high-pressure process for the carbonylation of methanol to acetic acid using an iodide-promoted cobalt catalyst (/, 2), and then in 1968, Paulik and Roth of Monsanto Company announced the discovery of a low-pressure carbonylation of methanol using an iodide-promoted rhodium or iridium catalyst (J). In 1970 Monsanto started up a large plant based on the rhodium catalyst. 

Acetic acid is presently produced on a very large scale. World-wide production in 1977 was approximately 2,500,000 tons. The Monsanto process has now been licensed world-wide, and production from these plants when constructed will amount to more than 1,000,000 tons annually. 

Process names which combine the name of a company with the name of a chemical, e.g. the Monsanto Acetic Acid process, have mostly been excluded because they are self-explanatory and can be found in the encyclopaedias. 

ENSOL A combined process for converting syngas to methanol and then to ethanol. Acetic acid is an intermediate. Developed by Humphries Glasgow, in conjunction with BASF and Monsanto. 

Monoterpenoid ketones, 24 536-541 Monoterpenoids, 24 468, 470, 472, 484-541 Monothiocarboxylic acids, 23 739 Monotropic phase transitions, 15 101 Monounsaturated fatty acids, 10 830 Monounsaturated olefins, hydrogenation of, 26 879-880 Monovinylacetylene, 1 230 Monsanto acetic acid process, 19 646 Monsanto adiponitrile process, 17 236 Monsanto aluminum chloride-based Alkylation process, 23 333 Monsanto Prism separator, 16 21 Monsanto process (Lummus-UOP Classic process), 16 74 23 339, 341 Monsanto-Washington University collaboration, 24 390, 400-401 Montanic acid... 

It is now nearly 40 years since the introduction by Monsanto of a rhodium-catalysed process for the production of acetic acid by carbonylation of methanol [1]. The so-called Monsanto process became the dominant method for manufacture of acetic acid and is one of the most successful examples of the commercial application of homogeneous catalysis. The rhodium-catalysed process was preceded by a cobalt-based system developed by BASF [2,3], which suffered from significantly lower selectivity and the necessity for much harsher conditions of temperature and pressure. Although the rhodium-catalysed system has much better activity and selectivity, the search has continued in recent years for new catalysts which improve efficiency even further. The strategies employed have involved either modifications to the rhodium-based system or the replacement of rhodium by another metal, in particular iridium. This chapter will describe some of the important recent advances in both rhodium- and iridium-catalysed methanol carbonylation. Particular emphasis will be placed on the fundamental organometallic chemistry and mechanistic understanding of these processes. 

One approach which enables lower water concentrations to be used for rhodium-catalysed methanol carbonylation is the addition of iodide salts, especially lithium iodide, as exemplified by the Hoechst-Celanese Acid Optimisation (AO) technology [30]. Iodide salt promoters allow carbonylation rates to be achieved at low (< 4 M) [H2O] that are comparable with those in the conventional Monsanto process (where [H20] > 10 M) while maintaining catalyst stability. In the absence of an iodide salt promoter, lowering the water concentration would result in a decrease in the proportion of Rh existing as [Rh(CO)2l2] . However, in the iodide-promoted process, a higher concentration of methyl acetate is also employed, which reacts with the other components as shown in Eqs. 3, 7 and 8 ... 

Monsanto developed the rhodium-catalysed process for the carbonylation of methanol to produce acetic acid in the late sixties. It is a large-scale operation employing a rhodium/iodide catalyst converting methanol and carbon monoxide into acetic acid. At standard conditions the reaction is thermodynamically allowed,... 

Figure 6.4. Process scheme Monsanto a= depressurisation, b= light ends removal, c= acetic acid...

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