Catalytic processes Monsanto process

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... 

In the Monsanto/Lummus Crest process (Figure 10-3), fresh ethylbenzene with recycled unconverted ethylbenzene are mixed with superheated steam. The steam acts as a heating medium and as a diluent. The endothermic reaction is carried out in multiple radial bed reactors filled with proprietary catalysts. Radial beds minimize pressure drops across the reactor. A simulation and optimization of styrene plant based on the Lummus Monsanto process has been done by Sundaram et al. Yields could be predicted, and with the help of an optimizer, the best operating conditions can be found. Figure 10-4 shows the effect of steam-to-EB ratio, temperature, and pressure on the equilibrium conversion of ethylbenzene. Alternative routes for producing styrene have been sought. One approach is to dimerize butadiene to 4-vinyl-1-cyclohexene, followed by catalytic dehydrogenation to styrene ... 

An early success story in the field of catalytic asymmetric synthesis is the Monsanto Process for the commercial synthesis of l-DOPA (4) (see Scheme 1), a rare amino acid that is effective in the treatment of Parkinson s disease.57 The Monsanto Process, the first commercialized catalytic asymmetric synthesis employing a chiral transition metal complex, was introduced by W. S. Knowles and coworkers and has been in operation since 1974. This large-scale process for the synthesis of l-DOPA (4) is based on catalytic asymmetric hydrogenation, and its development can be... 

Monsanto (2) A catalytic process for synthesizing the drag L-DOPA. The catalyst is a chiral diphosphine-rhodium complex. Invented in the early 1970s. 

One could call this type of electrocatalysis, which is due to the catalytic action of adsorbed species, electrocatalysis of the second kind. Most remarkably the selectivity and commercial success of the Monsanto process— the hydrodimerisation of arylonitrile to adipodinitrile—... 

As mentioned in the previous section, the carbonylation of methanol to acetic acid is an important industrial process. Whereas the [Co2(CO)s]-catalyzed, iodide-promoted reaction developed by BASF requires pressures of the order of 50 MPa, the Monsanto rhodium-catalyzed synthesis, which is also iodide promoted and which was discovered by Roth and co-workers, can be operated even at normal pressure, though somewhat higher pressures are used in the production units.4,1-413 The rhodium-catalyzed process gives a methanol conversion to acetic acid of 99%, against 90% for the cobalt reaction. The mechanism of the Monsanto process has been studied by Forster.414 The anionic complex m-[RhI2(CO)2]- (95) initiates the catalytic cycle, which is shown in Scheme 26. 

Catalytic asymmetric hydrogenation processes have been at the forefront of practical applications. Following the classical Monsanto s L-DOPA production using DiPAMP-Rh catalyst, BINAP-Ru catalysts have been used in the industrial synthesis of a P-lactam key intermediate to caibapenem antibiotics (Takasago Int. Corp.), 1,2-propanediol (50 tons/year),... 

The basic catalytic cycles and the catalytic intermediates for the Monsanto process are shown in Fig. 4.1. A variety of rhodium salts may be added to the reaction mixture as precatalysts. In the presence of I and CO they are quickly converted to complex 4.1. The following points about the catalytic cycles deserve special attention. 

Figure 4.1 Monsanto process, (a) The organometallic catalytic cycle CH3I and CO react to give CH3COI. (b) The organic catalytic cycle water and HI act as catalysts to generate acetic acid and CH3I from CH3COI and methanol.

The relevance of the water-gas shift reaction in the petrochemical industry has already been discussed (see Section 1.1). The significance of the water-gas shift reaction in homogeneous systems is twofold. First, it plays a crucial role in stabilizing the rhodium catalyst in the Monsanto process. Second, studies carried out in homogeneous systems employing metals other than rhodium have provided useful mechanistic insights into the heterogeneous water-gas shift reaction. We first discuss the catalytic cycle with 4.1 as one of the catalytic intermediates, and then mechanistic results that are available from an iron-based catalytic system. 

The proposed catalytic cycle for the water-gas shift reaction in the Monsanto process is shown in Fig. 4.5. This cycle operates at acidic pH and is responsible for C02 and H2 production. It has a useful function in stabilizing the rhodium... 

Assume that the basic mechanism of the Monsanto process is valid for the cobalt-based process. What would be the crucial hypothetical catalytic... 

The chemistry of acetyl-CoA synthesis is thought to resemble the Monsanto process for acetate synthesis in that a metal center binds a methyl group and CO and the CO undergoes a carbonyl insertion into the methyl-metal bond. Elimination of the acetyl group is catalyzed by a strong nucleophile, iodide in the industrial process and CoA in the biochemical one. Currently, there are two views of the catalytic mechanism. 

An important modern example of homogeneous catalysis is provided by the Monsanto process in which the rhodium compound 1.4 catalyses a reaction, resulting in the addition of carbon monoxide to methanol to form ethanoic acid (acetic acid). Another well-known process is hydro-formylation, in which the reaction of carbon monoxide and hydrogen with an alkene, RCH=CH2, forms an aldehyde, RCH2CH2CHO. Certain cobalt or rhodium compounds are effective catalysts for this reaction. In addition to catalytic applications, non-catalytic stoichiometric reactions of transition elements now play a major role in the production of fine organic chemicals and pharmaceuticals. 

The rhodium-catalyzed process gives a methanol conversion to acetic acid of 99%, against 90% for the cobalt reaction. The mechanism of the Monsanto process has been studied by Forster. The anionic complex c -[Rhl2(CO)2] (95) initiates the catalytic cycle, which is shown in Scheme 26. 

The Monsanto process, one of the most successful industrial homogeneous catalytic processes, uses a Rh complex and catalytic HI to carbonylate MeOH to MeC02H. A Rh precatalyst (almost any Rh complex will do) is converted into Rh(CO)2l2, the active catalyst, under the reaction conditions. The mechanism of the reaction involves three steps. In the first step, MeOH and HI are converted to Mel and H20 by an Sn2 mechanism. In the second step, Mel and CO are converted to MeCOI under Rh catalysis. In the third step, H2O (generated in the first step) hydrolyzes MeCOI to afford MeC02H and to regenerate HI. 

A key property of catalytic processes is selectivity. Catalysis has revolutionized process chemistry by replacement of wasteful, unselective (i.e. multiple-product-forming) reactions with efficient, selective (i.e. one-product-dominating) ones. For example, selective catalytic methanol carbonylation (practiced by BP, BASF Monsanto, Eastman) has to a large extent substituted unselective non-catalytic n-butane oxidation (Celanese, and Union Carbide processes). 

Carbonylation of methanol catalyzed by soluble Group IX transition metal complexes remains the dominant method for the commercial production of acetic acid. The Monsanto process stands as one of the major success stories of homogeneous catalysis, and for three decades it was the preferred technology because of the excellent activity and selectivity of the catalyst. It has been demonstrated by workers at Celanese, however, that addition of iodide salts can significantly benefit the process by improving the catalytic reaction rate and catalyst stability at low water concentrations. Many attempts have been made to enhance the activity of... 

Optimizing manufacturing processes is essential for financial reasons, and each catalytic process has potential problems that have to be overcome. One difficulty in the Monsanto process is the oxidation of CM-[Rh(CO)2l2] by HI (reaction 26.13), the product of which easily loses CO, resulting in the loss of the catalyst from the system (equation... 

Over the past 25 years, much effort has been put into investigating the use of r/-block organometallic clusters as homogeneous catalysts, and equations 26.23-26.25 give examples of small-scale catalytic reactions. Note that in reaction 26.23, insertion of CO is into the O—H bond in the Monsanto process using [Rh(CO)2l2] catalyst, CO insertion is into the C—OH bond (equation 26.12). 

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

The production of glyphosate herbicide (Round-up), the world s most successful herbicide, is another example of utilization of the catalytic properties of carbon surfaces [338], The Monsanto process by which Round-up is produced uses activated carbon as an oxidation catalyst for one of the key synthesis steps. The catalyst is produced by the treatment of activated carbon with ammonia at a high temperature to impart the desired nitrogen functionality. These functionalities are also commercially important for the reduction of chloramine in potable (drinking) water. Since water utilities are increasingly using chloramine rather than chlorine for water disinfection, and standard activated carbon products are not effective for removal of residual chloramine (which, for example, is highly toxic to dialysis patients), a catalytic carbon must be used to reduce its content [339,340],... 

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