Olefin Fischer-Tropsch reactions

The Fischer-Tropsch reaction is essentially that of Eq. XVIII-54 and is of great importance partly by itself and also as part of a coupled set of processes whereby steam or oxygen plus coal or coke is transformed into methane, olefins, alcohols, and gasolines. The first step is to produce a mixture of CO and H2 (called water-gas or synthesis gas ) by the high-temperature treatment of coal or coke with steam. The water-gas shift reaction CO + H2O = CO2 + H2 is then used to adjust the CO/H2 ratio for the feed to the Fischer-Tropsch or synthesis reactor. This last process was disclosed in 1913 and was extensively developed around 1925 by Fischer and Tropsch [268]. 

Fischer-Tropsch. Caibon monoxide is catalyticaily hydrogenated to a mixtuie of straight-chain aliphatic, olefinic, and oxygenated hydrocarbon molecules in the Fischer-Tropsch reaction (eq. 11) (see Fuels, synthetic). 

The hydroformylation reaction was discovered by Otto Roelen in 1938 (2,3) while investigating the influence of olefins on the Fischer-Tropsch reaction (/). Particularly in commercial publications, it has been termed the oxo reaction the more proper term, hydroformylation, was proposed by Adkins (4). 

An ex-carbonyl K-promoted alumina-supported catalyst prepared from Ru3(CO),2 and decarbonylated under H2 at 450°C was more dispersed and more active and selective for C2-C5 olefins in the Fischer-Tropsch reaction than conventionally prepared samples [108]. 

The Fischer-Tropsch reaction involves reduction of CO with H2 and combination with methanol and olefins in presence of various catalysts to produce an array of oxygenate products of high industrial values. 

CO + H2 -> paraffins + olefins + H20 + C02 (+ other oxygen-containing organic compounds) (Fischer-Tropsch reaction)... 

Modification of the zeolite appears to have affected the selectivity of Ru in these hydrogenation reactions. Exchange of K cations for Na cations in Y zeolite increases the basicity of the support (ref. 9). In Fischer-Tropsch reactions over similar catalysts, Ru/Y catalysts so modified yielded significant increases in the olefinic product fraction at the expense of paraffins. Olefins are believed to be primary products in F-T synthesis, with paraffins being produced from olefins in secondary hydrogenation reactions. In an analogous fashion, the Ru/KY catalyst used in the present study might also be expected to... 

Hydroformylation is a precious metal-catalyzed reaction of synthesis gas, a 1 1 mixture of hydrogen and carbon monoxide, and an olefinic organic compound to form aldehydes. The reaction was discovered by Otto Roelen in 1938 in experiments for the Fischer-Tropsch reaction [8]. In Scheme 3, hydroformylation of a terminal olefin is shown in which the addition of carbon monoxide can be conducted at both carbon atoms of the double bond, thus yielding linear (n) and branched (iso) aldehydes. 

The hydroformylation (or 0x0 ) reaction was discovered in 1938 by Roelen who was working on the formation of oxygenates as by-products of the Fischer-Tropsch reaction over cobalt catalysts. It soon became clear that the aldehydes and alcohols found were the products of secondary reactions undergone by the 1-alkenes (which are the primary products of the Fischer-Tropsch reaction, Section 4.7.2) with syngas. Further work showed that Roelen had discovered a new reaction, in which the elements of H and CHO were added to an olefin (hence hydroformylation), and which was catalyzed by cobalt. It was later found that the true precatalyst was not cobalt metal but derivatives of dicobalt octacarbonyl, such as the hydride, CoH(CO)4. 

As a matter of fact, olefin-consuming reactions (by H2) may be a serious problem in some technical reactions. Palladium complexes and Co2(CO)g (commercial products) are typical catalysts. Problems may also arise in the Fischer-Tropsch reaction [19, 20] where iron oxides of a certain basicity (alkaline-metal doping) are being used to catalyze the formation of hydrocarbons according to (the simplified) eq. (15). More details are provided in Section 3.1.8. Since water is inevitably formed, carbon dioxide can also occur. On the other hand, it is doubtful whether the CO/H2O system will be used for directed reductions of organic compounds, since hydrogen is an extremely abundant industrial chemical. The water-gas shift reaction is thus to be avoided in the vast majority of cases. 

From reaction (b), a new carbon-carbon bond is formed by the intermediacy of the transition metal. Several chemical processes in which new carbon-carbon bonds are formed (e.g., hydroformylation, olefin polymerization, homologation of alcohols, the Fischer-Tropsch reaction) are rationalized by a common mechanism of carbon chain growing. Much discussion and scientific work is under way to ascertain the general applicability of these findings to specific chemical or biochemical processes however, a basic understanding of the elementary steps involved in insertion reactions will lead to a better understanding of known reactions and to the development of new reactions. 

Readsorption and secondary reactions of the intiailly produced ct-olefins is an important pathway in Fischer-Tropsch reactions on Fe single crystals Dwyer, D.J., and Somorjai, G.A., J. Catal., 56, 249, (1979). Schulz, H., and Achtsnit,... 

Considerable work has been published concerning the incorporation of radioactive-isotope-labeled olefins in hydrocarbons during Fischer-Tropsch reactions. The pioneering work of Kummer and Emmett [89] and of Hall et al. [88] suggested that ethylene acted as a chain initiator over iron catalysts. The same results were obtained over cobalt catalyst by Eidus et al. [131]. 

The nonspecialist reader of this section may come to the conclusion that the area of transition-metal complexes with alkyldiazenido ligands is not very large. This impression is reinforced by the fact that these complexes lose the diazo group relatively easily, as mentioned in the beginning of the section. It is wrong, however, if one considers the fact that diazoalkanes have been used, and still are, extensively in the preparation of carbenes via metastable diazenido intermediates of metal-complex catalysts in laboratory scale syntheses, in the Fischer-Tropsch reaction, and in olefin metathesis (see, e.g., Herrmann, 1978 Doyle 1986a, 1986b and Sects. 8.7 and 8.8 of this book). 

One of the earliest reactions involving the insertion of CO into a Cn-olefin molecule to produce an aldehyde with one greater Cn+i carbon number is the so-called hydroformylation or "0x0 " reaction. The 0x0 reaction is carried out over homogeneous catalysts, rhodium or cobalt carbonyls, and is an important industrial process. Recently the production of acetic acid, acetaldehyde, and glycol from CO and H2 over heterogeneous and homogeneous rhodium catalysts have been reported. Straight-chain saturated hydrocarbons are not the only molecules that may be produced in the Fischer-Tropsch reaction. There have been... 

MPa total pressure, and H2 CO equal to 1.9. This may be a conservatively low value, as all the cobalt on the support may not be metallic. The value of Nco ior methanation at atmospheric pressure obtained by Vannice (12) on a 2% C0/AI2O3 catalyst, D = 0.08, was 4.6 X 10 sec" after extrapolation to 197°C. Furthermore, Vannice (12) obtained a — 0.5 order dependence on CO pressure. The two values of Nco for FT and methanation seem to be close. However, when compared with other reactions such as hydrogenation of olefins, where N at ambient conditions is about 1 sec (13), the Fischer-Tropsch reaction can be seen to be quite slow. 

The hydroformylation or oxo reaction, or oxo synthesis discovered by Otto Roelen and patented in 1938 (1) is the addition of carbon monoxide and dihydrogen to an olefin double bond in the presence of a transition metal complex as the catalyst. The discovery of the reaction regarding the cobalt catalyzed Fischer-Tropsch reactions. Roelen s observation that ethylene, H2, and CO were converted into propanal, and at higher pressures, diethyl ketone, marked the beginning of hydroformylation catalysis (2). The term of hydroformylation relates to the formal addition of hydrogen and a formyl group to the olefin substrate. 

Hydrocarbon synthesis from syngas (Fischer-Tropsch reactions) can be carried out over the catalysts prepared from Co- and Cu-containing LDHs. The products include methane, higher paraffins, and olefins as well as methanol. The loading of Co and Cu determines the selectivity for each compound. For instance, Co-rich catalysts give more paraffins, while Co-poor ones lead to methanol (615). 

Pioneering studies by Emmet suggested in 1953 that ethylene acts as a chain initiator in Fe-catalyzed Fischer-Tropsch reactions. Many authors have used isotopi-cally labeled olefins to confirm that 1-alkenes are the primary reaction products (although they are thermodynamically instable under the reaction conditions). For instance, Somorjai s group has shown, using a polycrystalline iron sheet (1 cm ), that the addition of ethylene or propene in the syn gas increases the length of the polymer chain. These olefins readsorb and readily form polymers by insertion into adsorbed C fragments. Thus, the Fischer-Tropsch mechanism involves two steps, namelly the formation of olefins and their polymerization ... 

J. Barrault, C. Forquy, and V. Perrichon, Effects of manganese oxide and sulphate on olefin selectivity of iron supported catalysts in the Fischer-Tropsch reaction, Applied Catalysis, vol. 5, no. 1, pp. 119—125, 1983. 

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