Monsanto acetic acid process catalysts used

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... 

Organometallic compounds are used widely as homogeneous catalysts in the chemical industry. For example, if the alkene insertion reaction continues with further alkene inserting into the M C bond, it can form the basis for catalytic alkene polymerisation. Other catalytic cycles may include oxidative addition and reductive elimination steps. Figure above shows the steps involved in the Monsanto acetic acid process, which performs the conversion... 

Cativa A process for making acetic acid by reacting methanol with carbon monoxide (carbonylation). The catalyst contains iridium acetate with promoters. Developed joindy by BP Chemicals, Hull, UK, and the University of Sheffield. First announced in 1996 and installed between 1995 and 1999 in four plants that had been using the former Monsanto acetic acid process. The first plant designed for the process was built by BP Petronas in Malaysia in 2000. A joint venture of BP with Sinopec used the process in a plant expansion in Chongqing, China, in 2005, and planned to build another plant in Nanjing, for completion in 2007. 

The WGSR is normally practised as a heterogeneously metal-catalyzed reaction Fe is the most commonly used catalyst. However other metals are also active, for example the homogeneous Rh/H catalyst in the Monsanto acetic acid process (Section 4.2.4) concurrently catalyzes the WGSR via a Rh(I)/ Rh(III) cycle (Equations 8 and 9),... 

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) ... 

The main difference between the Monsanto acetic acid process and Tennessee Eastman acetic anhydride process is the presence of water in the acetic acid process, which produces HI and acetic acid. In both reactions, a small amount of H2 is added to the CO stream to act as a reducing agent to keep the catalyst in the more active Rh oxidation state. An engineering problem with both processes is the highly corrosive nature of the Hl/iodide mixture, requiring the use of special chemically resistant alloys, pumps, and seals. 

Acetyl CoA synthetase (ACS) is capable of forming acetyl coenzyme A (Ac-SCoA) from carbon monoxide, CHj, and HSCoA. The so-called A cluster of ACS features a tetradentate tripeptide motif Cys-Gly-Cys accommodating two nickel centers [42] for oxidative addition of CHj, migratory insertion of CO, and, finally, reductive elimination of C0A-SCOCH3. Interestingly, this mechanism strongly resembles the Monsanto acetic acid process using cis-[Rh l2(CO)2] as catalyst. 

It may be considered ironic that as early as 1969 a nearly complete description of the characteristic features of the subsequently presented LPO technology had been published by Monsanto researchers [5]. The company decided at that stage not to deal with hydroformylation any longer, but instead they concentrated on the development of the nowadays well-known acetic acid process (using modified rhodium carbonyl as catalyst) (cf. Section 2.1.2.1) [6]. 

Acetic acid is a key commodity building block [1], Its most important derivative, vinyl acetate monomer, is the largest and fastest growing outlet for acetic acid. It accounts for an estimated 40 % of the total global acetic acid consumption. The majority of the remaining worldwide acetic acid production is used to manufacture other acetate esters (i.e., cellulose acetates from acetic anhydride and ethyl, propyl, and butyl esters) and monoehloroacetic acid. Acetic acid is also used as a solvent in the manufacture of terephthalic acid [2] (cf. Section 2.8.1.2). Since Monsanto commercially introduced the rhodium- catalyzed carbonylation process Monsanto process ) in 1970, over 90 % of all new acetic acid capacity worldwide is produced by this process [2], Currently, more than 50 % of the annual world acetic acid capacity of 7 million metric tons is derived from the methanol carbonylation process [2]. The low-pressure reaction conditions, the high catalyst activity, and exceptional product selectivity are key factors for the success of this process in the acetic acid industry [13]. 

Several important homogeneous catalytic reactions (e.g. hydroformylations) have been accomplished in water by use of water-soluble catalysts in some instances water can act as a solvent and as a reactant for hydroformylation. In addition, formation of aluminoxanes by partial hydrolysis of alkylaluminum halides results in very high activity bimetallic Al/Ti or Al/Zr metallocene catalysts for ethene polymerization which would be otherwise inactive. Polymerization of aryl diiodides and acetylene gas has recently been achieved in water with palladium catalysts. Finally, nickel-containing enzymes, such as carbon monoxide dehydrogenase (CODH) and acetyl-CoA synthase, operate in water with reaction mechanisms comparable with those of the WGSR or of the Monsanto methanol-to-acetic-acid process. ... 

The production of another important chemical and polymer intermediate, acetic acid, was revolutionized by the Wacker process that was introduced in 1960. It was a simple, high yield process for converting ethylene to acetaldehyde, which replaced the older process based on ethanol and acetylene. In the Wacker reaction, the palladium catalyst is reduced and then reoxidized. Ethylene reacts with water and palladium chloride to produce acetaldehyde and palladium metal. The palladium metal is reoxidized by reaction with cupric chloride, which is regenerated by reaction with o gen and hydrochloric acid. In 1968, BASF commercialized an acetic acid process based on the reaction of carbon monoxide and methanol, using carbonyl cobalt promoted with an iodide ion (74). Two years later, however, Monsanto scored a major success with its rhodium salt catalyst with methyl iodide promoter. Developed by James F. Roth, this new catalyst allowed operation at much milder conditions (180°C, 30-40 atm) and demonstrated high selectivity for acetic acid (75). 

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. 

Methanol process. BASF introduced high-pressure technology way back in I960 to make acetic acid out of methanol and carbon monoxide instead of ethylene. Monsanto subsequently improved the process by catalysis, using an iodide-promoted rhodium catalyst. This permits operations at much lower pressures and temperatures. The methanol and carbon monoxide, of course, come from a synthesis gas plant. 

Another way to produce acetic acid is based on a carbonylation of methanol in the so called Monsanto process, which is the dominant technology for the production of acetic acid today [15]. Acetic acid then is converted to VAM by addition of ethylene to acetic acid in the gas phase using heterogeneous catalysts usually based on palladium, cadmium, gold and its alloys (vinylation reaction 3 in Fig. 2) [16] supported on silica structures. 

Acetic Acid. Carbonylation of methanol is the most important reaction in the production of acetic acid.189-192 BASF developed a process applying C0I2 in the liquid phase under extreme reaction conditions (250°C, 650 atm).122 193 The Monsanto low-pressure process, in contrast, uses a more active catalyst combining a rhodium compound, a phosphine, and an iodine compound (in the form of HI, Mel, or T2).122 194—196 Methanol diluted with water to suppress the formation of methyl acetate is reacted under mild conditions (150-200°C, 33-65 atm) to produce acetic acid with 99% selectivity at 100% conversion. 

Using methanol, a variety of fine diemicals can be made by conventional and new ways. Homogeneous catalysts have already contributed here. In tills connection the acetic acid synthesis by Monsanto must be mentioned [28]. Scheme 7 summarizes processes based on methanol, which arc under consideration or already at the development stage. 

Using the catalyst system known from the Monsanto process, Dumas et at. have been able to direct the reaction towards ethanol formation using syngas mixtures extremely rich in hydrogen [87]. As is shown in Table XII, no acetic acid and only minor amounts of acetates are formed at an H3/CO ratio of 60. Ethanol and acetaldehyde aie the main products along with considerable amounts of methyl ethyl ether. Unfortunately, the Dumas c/ at. based the yields and conversion on carbon monoxide and not on methanol. This makes the data of this interesting process difficult to compare with those of other catalyst systems. 

The Monsanto process to acetic acid uses a rhodium-iodine-containing catalyst to convert a mixture of methanol and carbon monoxide under mild conditions and ambient pressure to very high (994-% based on methanol) yields of the product (Eq. 19.18) [16]. Several stages of distillation are required to recover the acetic acid (b.p. 118°C) in purities of 99.8% or... 

RhCI(CO)2]2 is formed in the reaction of RhCl, and CO, and both [RhCl(CO)2]2 and RhCI, are used as catalyst precursors in the carbonylation of methanol to acetic acid, the so-called Monsanto process (eq (29)) [36]. In this reaction, methyl iodide is necessary as a promoter and [Rhl2(CO)2] is proposed as the active species. 

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