Fischer-Tropsch reaction system

A Fischer-Tropsch catalyst system capable of linking reactions (14) and (16), i.e., a synthesis catalyst having appreciable shift activity, would clearly be of considerable interest in that it would allow the use of hydrogen-poor synthesis gas for the production of hydrocarbons via the following overall reaction ... 

Dyotropic Rearrangements and Related o--cr Exchange Processes, 16, 33 Electronic Effects in Metallocenes and Certain Related Systems, 10, 79 Electronic Structure of Alkali Metal Adducts of Aromatic Hydrocarbons, 2, 115 Fast Exchange Reactions of Group I, II, and III Organometallic Compounds, 8, 167 Fischer-Tropsch Reaction, 17, 61 Flurocarbon Derivatives of Metals, 1, 143... 

The actual structure of the active catalyst in the above reactions is a matter of speculation. The evidence, however, points to the presence of a homogeneous but immobilized Fischer-Tropsch catalyst. Since soluble CpCo(CO)2 does not possess Fischer-Tropsch activity, this activity is a unique feature of the polymer-bound system. The finding that 5 is regenerated quantitatively upon exposure of the active Fischer-Tropsch catalyst resin to CO implies that the n5-cyclopentadienylcobalt bond remains intact throughout the Fischer-Tropsch reaction. Similar... 

Another reactor system which has several attractive features for heat removal is the tubular, heat-exchange reactor. Good temperature control can be achieved in the tubular reactor if the coolant approximates an isothermal heat sink. Light gas recycle can be reduced significantly compared to fixed-bed systems. Tubular reactors have been used for Fischer-Tropsch reactions and for synthesis of methanol and phthalic anhydride, for example. 

Some mechanistic information is available on ruthenium-based homogeneous Fischer-Tropsch reactions. By in situ IR spectroscopy, in the absence of any promoter, only Ru(CO)5 is observed. An important difference between the cobalt and the rhodium system on the one hand and ruthenium on the other is that in the latter case no ethylene glycol or higher alcohols are obtained. In other words, in the catalytic cycle the hydroxymethyl route is avoided. 

These mixed metal systems have also been tested with the transient method for catalytic activity in the Fischer-Tropsch reaction. We would like to remark here that the nature of the cation, anion, and zeolite are all important factors in the Fischer-Tropsch reactions that we have studied. Further details of these catalytic studies can be found elsewhere (23). We do observe here, however, that some catalysts that are completely reduced to the metallic state are not necessarily the most active catalysts. Also, even though the Mossbauer experiments suggest that 400°C is sufficient for complete reduction, higher activation temperatures can increase the activity and selectivity of these reactions. We have also observed that the cation definitely changes the product distribution and the activity. 

In this paper, we will review the chemical behaviour of transition metal oxides which is of crucial importance for heterogeneous catalysis, adhesion and many technological applications. Among them, MgO(lOO) is the simplest surface, with a square unit-cell containing two ions with opposite charges titanium oxides represent another important class of systems used for their catalytic properties either directly as catalyst or indirectly as support for other catalysts (metals such as Ni, Rh for the Fischer-Tropsch reaction or V2O5 for the reduction of NOx) or as promotors[l]. The most stable surface for rutile is the (110) face. 

Fig. 12. Fischer-Tropsch reaction at 1 atm is first-order in CO, with an activation energy of 27 kcal/ mole (Lancet, 1972). Rate in a flow system is 10 times faster than in the static system used here. Dashed line shows extrapolation to solar nebula, assuming that the rate is proportional to (PcoIIPhj) . Reaction proceeds at an undetectable rate when the Bruderheim L6 chondrite is used as a catalyst. Apparently the high-temperature minerals in this meteorite (olivine, orthopyroxene, troilite, and nickel-iron) do not catalyze the hydrogenation of CO. Thus CO can survive in the solar nebula down to 400 K, when catalytically active minerals first from (Fig. 1 and 10)...

In our own solar system, nearly all volatiles complementary to the inner planets (3 X 10 Mg) were so lost. Earth and Venus contain only about 10 their complement of C, and even lesser amounts of H O, N, and noble gases. Since the retained C appears to show the imprint of the Fischer-Tropsch reaction, it seems likely that the lost C, too, had been involved in this process. 

Another system in this class of mechanisms that was also modeled mathematically is the technically important Fischer-Tropsch process on Fe catalysts investigated by Caldwell (217,218). Oscillation had been previously observed in this system by Tsotsis and co-workers (279). Caldwell reduced the mechanism of the Fischer-Tropsch reaction to three reactions ... 

The catalytically active phase was assumed to be exclusively a-Fe, and Fe304 was assumed not to be active for the Fischer-Tropsch reaction. Kinetic parameters for the simulations were obtained independently in separate oxidation/reduction studies. Balancing the oxidation and reduction rates for the CO/CO2 and the H2/H2O systems independently and describing the rate of synthesis in Fischer-Tropsch reactions by a standard expression, Caldwell could predict the oscillations with a simplified model for a tubular reactor fairly well. 

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. 

Like Rh/1 systems, the Ir4(CO),2/l2 system catalyzes the carbonylation of methanol to acetic acid [70]. In homogeneous hydrogenation of CO (Fischer Tropsch reaction), Ir4(CO)i2 shows a relatively high catalytic activity compared with other transition metal carbonyls (eq (62)) [71]. 

A. first-of-a-kind multifunctional catalytic system is being developed to convert synthesis gas into synthetic crude via the Fischer-Tropsch reaction. This is achieved through intensification of chemical reaction and heat and mass transport processes within the catalyst system. Tbe synergistic integration of intensified unit operations with chemical reaction leads to enhanced catalyst performance and significant economic advantages. 

Related Ru systems have been prepared on Na X-zeolite. While these were active for the hydroformylation of ethene at 10 MPa and 200 °C, appreciable amounts of products from competing ethene dimerization or Fischer-Tropsch reactions were also observed and significant Ru elution occurred. 

The Fischer-Tropsch reaction of carbon monoxide with hydrogen can be described, in a simplified way, according to equation (8.9). Chain growth proceeds at the surface of cobalt- and/or iron-based catalyst systems, e.g. Fe-, Fe/Co-, Fe/Co-Spinel-, Co/Mn-Spinel- or Cu-doped Co-catalysts. Iron catalysts, on the one hand, are cheaper than cobalt catalysts and more flexible as well as resistant with respect to syngas composition and quality. Cobalt catalysts, on the other hand, exhibit best performances at a H2 CO ratio of... 

Maitlis has reviewed the homogeneous and heterogeneous systems and noted that the former produce mainly oxygenated products, such as alcohols and esters. Most of the recent work on the Fischer-Tropsch reaction has focused on heterogeneous catalysts. The mechanism(s) of the later ate mainly inferred from isotope labeling and product distributions. The observations and mechanistic proposals of the Sheffield group have been summarized by Maitlis. However, there is still some controversy about the heterogeneous pathways. ... 

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