Carbon monoxide high pressure catalytic reactions

Studies on Some High-Pressure Catalytic Reactions of Carbon Monoxide... 

HIGH-PRESSURE CATALYTIC REACTIONS OF CARBON MONOXIDE 621... 

The catalytic dicarbonylation of ethylene to dimethyl succinate can be carried out in 90% conversion.94 High reaction temperatures and low carbon monoxide pressures can lead to unsaturated esters as a result of a faster -hydride elimination from the intermediate (23) than carbon monoxide insertion. This later reaction path has been termed oxidative carboxylation. 

Today, most methanol is synthesized by a catalytic reaction of carbon monoxide with hydrogen. This reaction uses high temperatures and pressures and requires large, complicated industrial reactors. 

Liquid propylene, gaseous carbon monoxide and hydrogen, and a soluble cobalt catalyst are fed to a high-pressure catalytic reactor. The reactor effluent goes to a flash tank, where all of the solution constituents are vaporized except the catalyst, which is recycled to the reactor. The reaction products are separated from unconsumed reactants in a multiple-unit process, and the product stream, which contains both butyraldehyde and /i-butanol, is subjected to additional hydrogenation with excess hydrogen, converting all of the butyraldehyde to butanol. 

Walter Reppe (1892-1969) was the research director of Badische Anilin- Sodafabrik (BASF) at Ludwigshafen, Germany. His research included metal-catalyzed reactions of acetylene (1938) and of carbon monoxide (1939) (Section 2.1.2.2). High-pressure catalytic acetylene chemistry is nowadays named after him. He also discovered the metal carbonyl-catalyzed cyclooligomerization of acetylene to yield styrene, benzene, and cyclooctatetraene (1948) [10, 77]. 

Carbon monoxide can be catalytically converted into methane in a high-pressure reactor. The reaction kinetics is given by the expression... 

As a result of the kinetics and the equilibria mentioned above, all iodide in the system occurs as methyl iodide. The reaction in Equation (2) makes the rate of the catalytic process independent of the methanol concentration. Within the operation window of the process, the reaction rate is independent of the carbon monoxide pressure. The selectivity in methanol is in the high 90s but the selectivity in carbon monoxide may be as low as 90%. This is due to the water-gas shift reaction ... 

Of the three catalytic systems so far recognized as being capable of giving fast reaction rates for methanol carbonylation—namely, iodide-promoted cobalt, rhodium, and iridium—two are operated commercially on a large scale. The cobalt and rhodium processes manifest some marked differences in the reaction area (4) (see Table I). The lower reactivity of the cobalt system requires high reaction temperatures. Very high partial pressures of carbon monoxide are then required in the cobalt system to... 

The first catalyst used in hydroformylation was cobalt. Under hydroformylation conditions at high pressure of carbon monoxide and hydrogen, a hydrido-cobalt-tetracarbonyl complex (HCo(CO)4) is formed from precursors like cobalt acetate (Fig. 4). This complex is commonly accepted as the catalytic active species in the cobalt-catalyzed hydroformylation entering the reaction cycle according to Heck and Breslow (1960) (Fig. 5) [20-23]. 

High-pressure in-situ NMR spectroscopy have been reported about reactions of carbon monoxide with cobalt complexes of the type, [Co(CO)3L]2. For L=P(n-C4H9)3, high pressures of carbon monoxide cause CO addition and disproportionation of the catalyst to produce a catalytically inactive cobalt(I) salt with the composition [Co(CO)3L2]+[Co(CO)4] . Salt formation is favoured by polar solvents [13],... 

High pressure infrared (HP IR) spectroscopy has now been used for over 30 years for the study of homogeneous transition metal catalysed processes. The technique is particularly useful for reactions involving carbon monoxide, for which transition metal carbonyl complexes are key intermediates in the catalytic mechanisms. Such complexes have one or more strong r(CO) absorptions, the frequencies and relative intensities of which provide information about the geometry and electronic character of the metal center. As well as probing the metal species, HP IR spectroscopy can also be used to monitor the depletion and formation of organic reactants and products if they have appropriate IR absorptions. 

The picture is different for the bimetallic ruthenium-rhodium systems both metals in the presence of iodide promoters and CO give anionic iodocarbonyl species, namely [Ru(C0) I ] and [Rh(CO)2l2] j but the range of I, CO concentration and temperature in which the anions exist and are catalytically active in carbonylation reactions is different. [Ru(CO)3l2] species in fact are extensively transformed at high temperature and low carbon monoxide pressure by an excess of I (i.e. I/Ru 50) into catalytically inactive [Ru(CO)2l4] (v q 2047, 1990 cm"l in THF (JJ.)) (eq. 1), whereas [Rh(CO)2l2] can work in the carbonylation process only in the presence of a large excess of I"" (I/Rh 100-1000) which prevents reduction to metal (12) (for instance at 150 C rhodium(I) carbonyl halides, [Rh(CO) X2]"", without CH3I under a CO/H2 pressure of 10 MPa are completely reduced to metal). 

Livinghouse and co-workers finally refined the catalytic PKR employing Co2(CO)s (5 mol%) and expanded the scope of the reaction. They first reported the protocol, in which the photoactivated Co2(CO)8 was used under the atmospheric pressure of carbon monoxide. Next, they revealed the thermal condition, keeping the reaction tempera-ture in a very narrow range (50-55 °G). The high purity of Co2(CO)8 is another provision to ensure... 

Chung provided one of the simple solutions based on this line of concept. Under the high pressure of carbon monoxide, the higher homolog of cobalt carbonyls including Co4(CO)i2 is depressed, and the considerable amount of Co2(CO)8 becomes available. This is now used for the catalytic reaction at high temperature of 150 °C. 

Reaction (78) regenerates Mel from methanol and HI. Using a high-pressure IR cell at 0.6 MPa, complex (95) was found to be the main species present under catalytic conditions, and the oxidative addition of Mel was therefore assumed to be the rate determining step. The water-gas shift reaction (equation 70) also occurs during the process, causing a limited loss of carbon monoxide. A review of the cobalt-, rhodium- and iridium-catalyzed carbonylation of methanol to acetic acid is available.415... 

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