Monsanto process acetic acid manufacture

The third and now preferred method of acetic acid manufacture is the carbonylation of methanol (Monsanto process), involving reaction of methanol and carbon monoxide (both derived from methane). This is discussed in Chapter 12, Section 3. 

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

The last method is the most economical among the four, and is employed in most new acetic acid manufacturing facilities throughout the world. Monsanto was awarded the Kirkpatrick Chemical Engineering Merit Award in 1976 for the development of this process. 

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. 

Acetic Acid. Although at the time of this writing Monsanto s Rh-catalyzed methanol carbonylation (see Section 7.2.4) is the predominant process in the manufacture of acetic acid, providing about 95% of the world s production, some acetic acid is still produced by the air oxidation of n-butane or light naphtha. n-Butane is used mainly in the United States, whereas light naphtha fractions from petroleum refining are the main feedstock in Europe. 

The recent dramatic increase in the price of petroleum feedstocks has made the search for high selectivities more urgent. Several new processes based on carbon monoxide sources are currently competing with older oxidation processes.103,104 The more straightforward synthesis of acetic acid from methanol carbonylation (Monsanto process) has made the Wacker process obsolete for the manufacture of acetaldehyde, which used to be one of the main acetic acid precursors. Several new methods for the synthesis of ethylene glycol have also recently emerged and will compete with the epoxidation of ethylene, which is not sufficiently selective. The direct synthesis of ethylene... 

In this chapter we discuss the mechanistic and other details of a few industrial carbonylation processes. These are carbonylation of methanol to acetic acid, methyl acetate to acetic anhydride, propyne to methyl methacrylate, and benzyl chloride to phenyl acetic acid. Both Monsanto and BASF manufacture acetic acid by methanol carbonylation, Reaction 4.1. The BASF process is older than the Monsanto process. The catalysts and the reaction conditions for the two processes are also different and are compared in the next section. Carbonylation of methyl acetate to acetic anhydride, according to reaction 4.2, is a successful industrial process that has been developed by Eastman Kodak. The carbonylation of propyne (methyl acetylene) in methanol to give methyl methacrylate has recently been commercialized by Shell. The Montedison carbonylation process for the manufacture of phenyl acetic acid from benzyl chloride is noteworthy for the clever combination of phase-transfer and organometallic catalyses. Hoechst has recently reported a novel carbonylation process for the drug ibuprofen. 

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]. 

The future of the commercial acetaldehyde processes mainly depends on the availability of cheap ethylene. Acetaldehyde has been replaced as a precursor for 2-ethylhexanol ( aldol route ) or acetic acid (via oxidation cf. Sections 2.1.2.1 and 2.4.4). New processes for the manufacture of acetic acid are the Monsanto process (carbonylation of methanol, cf. Section 2.1.2.1), the Showa Denko one-step gas-phase oxidation of ethylene with a Pd-heteropolyacid catalyst [75, 76], and Wacker butene oxidation [77]. Other outlets for acetaldehyde such as pentaerythritol and pyridines cannot fill the large world production capacities. Only the present low price of ethylene keeps the Wacker process still attractive. 

The synthesis of acetic acid is one of the most rapidly growing chemical applications for methanol. The process for manufacture of acetic acid was developed by Monsanto. The reaction runs at a temperature of 150-200°C and a pressure of 30.62 atm. The catalyst used is rhodium salts with certain ligands and in the presence of an iodine compound. The reaction is ... 

In 1970, the discovery of these new organo-soluble catalysts based on Rh, Pd, or Pt was generally considered unfeasible for industrial processes because of the prohibitive price of the metals involved. However, the hgh activity and productivity of these catalysts made possible production levels of 100000 ty 1 with only a few dozen kilograms of precious metals needed as inventory by each single plant. Thus, the amount of precious metal involved represents only a minor part of the investment and the manufacturing costs, i.e., the price of the metal was not an important factor in the production unit cost, provided that its usage occurred without any loss. In 1972 this hypothesis was confirmed by Monsanto and its commercialization of the important process to generate acetic acid by methanol carbonylation [16]. 

The major catalytic uses involve the complex cis-[Rh(CO)2l2] in the Monsanto acetic acid and Termessee-Eastman acetic anhydride processes, discussed in detail in Section 26.4. Application of iodine as a stabilizer includes its incorporation into nylon used in carpet and t5re manufacture. Iodized animal feed supplements are responsible for reduced instances of goitre (enlarged thyroid gland) which are otherwise prevalent in regions where the iodine content... 

Table 26.3 Major advantages of the Monsanto process over the BASF process for the manufacture of acetic acid (equation 26.12) can be seen from the summary in this table.

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

The major end-use of iodine is in catalysis (e.g., the Monsanto process for producing acetic acid). Titanium tetraiodide and aluminum iodide are also significant in the dehydrogenation of butane and butene to butadiene, and in the preparation of stereoregular polymers. The second major end-use of iodine is as a stabilizer in the manufacture of nylon, for converting resins, tall oil and other wood products to more stable forms, while the third major use is as additives for animal and human food (iodization of salt and mineral mixtures). 

Worldwide production of acetic acid is dominated by the BP Chemicals methanol carbonylation process originally developed by Monsanto in the 1960s. Previously, acetic acid was manufactured by air-based oxidation of acetaldehyde or light hydrocarbons. Currently about of the acetic acid... 

The conversion of MeOH to MeC02H (equation 27.15) is carried out on a huge industrial scale, and 60% of the world s acetyls are manufactured using the Monsanto process. Currently, 7Mt per year of acetic acid are... 

Nowadays, iodine is widely used for the manufacturing of X-ray contrast media, antimicrobial products, as tinctures of polyvinylpyrrolidone-iodine (Povidone-iodine), catalysts in chemical processes (e.g. for the production of acetic acid by carbonylation of methanol in the presence of a rhodium iodide-catalyst (Monsanto process) or an iridium iodide-catalyst (Cativa process)), and also on a smaller scale for the production of pharmaceuticals like thyroid hormones. [ 83 ]... 

Applications and uses. Carbon monoxide is a major industrial gas that has many applications in bulk chemicals manufacturing, including the production of methanol by hydrogenation and aldehydes by the hydroformylation reaction. It is also used in the industrial production of phosgene. Carbon monoxide and methanol react in the presence of a homogeneous rhodium catalyst and HI to give acetic acid in the Monsanto process, which is responsible for most of the industrial production of acetic acid. 

Interesting news was released by Monsanto [1011, 1012] who reported that they are going to build a large acetic acid plant at Texas City for startup in 1970. Acetic acid will be manufactured by low pressure carbonylation of methanol using a rhodium catalyst together with a halogen promotor [1009, 1010, 1013] instead of cobalt catalyst, which is used in the BASF process. 

Before 1970, acetic acid was manufactured by the BASF process utilizing cobalt-based catalysts, and high temperatures and pressures. Replacement of this procedure by the Monsanto process brought advantages of milder conditions and greater selectivity (Table 25.3). The Monsanto process uses a rhodium-based catalyst, and involves two interrelated... 

Table 25.3 Comparison of conditions and selectivities of the BASF, Monsanto and Cativa processes for the manufacture of acetic acid (eq. 25.15).

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