Carbonylation industrial operations

Elemental sulfur1-4 occurs naturally in association with volcanic vents and, in Texas and Louisiana, as underground deposits. The latter are mined by injecting air and superheated water, which melts the sulfur and carries it to the surface in the return flow (the Frasch process). Most of the sulfur used in industry, however, comes as a by-product of the desulfurization of fossil fuels. For example, Albertan sour natural gas, which often contains over 30% (90%, in some cases) hydrogen sulfide (H2S), as well as hydrocarbons (mainly methane) and small amounts of C02, carbonyl sulfide (COS), and water, is sweetened by scrubbing out the H2S and then converting it to elemental S in the Claus process.5 The Claus process is applicable in any industrial operation that produces H2S (see Section 8.5) it converts this highly toxic gas to nontoxic, relatively unreactive, and easily transportable solid sulfur. 

There are two competitive processes for the manufacture of DMC. In the UBE process, developed on an industrial scale in Japan, methyl nitrite is exploited as an intermediate, which is generated in a separate step by reaction of methanol, NO, and O2. Then, a fixed bed, palladiumotalyzed carbonylation of methyl nitrite takes place in the gas phase. PdCl2/CuCl2 on active carbon is believed to be used in the actual industrial operation. 

Under the conditions of industrial operation, the rate of methanol carbonylation reaction has been found to be zeroth order in the partial pressure... 

The subject has been reviewed (37,38). Water may be added to the feed to suppress methyl acetate formation, but is probably not when operating on an industrial scale. Water increase methanol conversion, but it is involved in the unavoidable loss of carbon monoxide. A typical methanol carbonylation flow sheet is given in Figure 2. 

Wm. Haynes Well, we suspect that the carbonyl is formed in almost any part of the system that is composed of carbon steel, which has a temperature of about 100 °C, and which is under a high pressure of CO. So, we feel that parts of the system that would be operating under these conditions would have to be lined with copper or a relatively inert material like that. In fact, it is the practice in the methanol industry to have the vessels copper lined. 

The direct conversion of alcohols and amines into carbamate esters by oxidative carbonylation is also an attractive process from an industrial point of view, since carbamates are useful intermediates for the production of polyurethanes. Many efforts have, therefore, been devoted to the development of efficient catalysts able to operate under relatively mild conditions. The reaction, when applied to amino alcohols, allows a convenient synthesis of cyclic urethanes. Several transition metal complexes, based on Pd [218— 239], Cu [240-242], Au [243,244], Os [245], Rh [237,238,246,247], Co [248], Mn [249], Ru [224,250-252], Pt [238] are able to promote the process. The formation of ureas, oxamates, or oxamides as byproducts can in some cases lower the selectivity towards carbamates. 

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]. 

In this chapter, the recent advances in amidocarbonylations, cyclohydrocarbonylations, aminocarbonylations, cascade carbonylative cyclizations, carbonylative ring-expansion reactions, thiocarbonylations, and related reactions are reviewed and the scope and mechanisms of these reactions are discussed. It is clear that these carbonylation reactions play important roles in synthetic organic chemistry as well as organometallic chemistry. Some of the reactions have already been used in industrial processes and many others have high potential to become commercial processes in the future. The use of microwave irradiation and substitutes of carbon monoxide has made carbonylation processes suitable for combinatorial chemistry and laboratory syntheses without using carbon monoxide gas. The use of non-conventional reaction media such as SCCO2 and ionic liquids makes product separation and catalyst recovery/reuse easier. Thus, these processes can be operated in an environmentally friendly manner. Judging from the innovative developments in various carbonylations in the last decade, it is easy to anticipate that newer and creative advances will be made in the next decade in carbonylation reactions and processes. 

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. 

Ube Industries LtdinYamaguchi, Japan, and Kyoto University investigated the Swern oxidation for pharmaceutical intermediates [57,58]. In this reaction, alcohols are oxidized to carbonyl compounds using dimethyl sulfoxide. The reaction variant using dimethyl sulfoxide activated by trifluoroacetic anhydride (shown below) has found industrial application, but is limited to low-temperature operation (—50 °C or below) to avoid decomposition of an intermediate. 

Carbonylation of methanol has in recent years become a commercially important route for the production of acetic acid and methyl acetate. Industrial catalysts are at present homogeneous, based on cobalt and more recently rhodium compounds. The cobalt catalysts are less active 195) and require more severe operating conditions (i.e., 250°C, 650-750 atm) than the rhodium-based catalysts 196) (170-250°C, 7-14 atm). 

In addition a very useful and frequently applied method in the fine chemical industry to convert alcohols into the corresponding carbonyl compounds is the use of oxoammonium salts as oxidants [15]. These are very selective oxidants for alcohols, which operate under mild conditions and tolerate a large variety of functional groups. 

The literature of biphasic hydrogenations contains plenty of substrates (al-kenes and cycloalkenes, arylaliphatic olefins, carbonyl compounds, etc.), mainly with TPPMS as water-soluble ligand (solubility approx. 200 g/1 [150] as compared with 1100 g/1 with TPPTS [37]). So far, no industrial process has been derived from these smdies. Besides the development of the basics of biphasic operation, the research concentrates on fundamental work concerning the question of where the reaction takes place phase boundary, organic phase, or aqueous phase. Wilkinson [29] concluded from his hydrogenation tests with hexenes or cyclohexenes in the presence of TPPMS that the somewhat lower rate of hydrogenation as compared with monophasic conversion should be due to the necessary diffusion of the hydrogen to the alkene/water interface. In this way the iso-... 

Utne and coworkers [36] measured the emissions of carbonyl sulfide from industrial cells during normal operation. High levels of COS were found in the undiluted/unoxidized anode gas amounts corresponded to 3.3-10.2 kg tonne-1 of aluminum produced. Most of the sulfur emitted from the cells appears to originate from sulfur in the anodes. However, the COS is oxidized as the anode gasses leave the cell. After the gasses pass through dry and then wet scrubbing, the COS content corresponds to 0.21-0.26 kg tonne-1 Al. 

Copper compounds, besides being the most widely used co-catalysts for palladium re-oxidation, are themselves active in DMC formation. Exploiting the catalytic properties of CuCl, EniChem developed its DMC production process of one-step oxy-carbonylation of methanol. This process has operated industrially since 1983. 

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