Reactions of Synthesis Gas

Fischer-Tropsch Process. The Hterature on the hydrogenation of carbon monoxide dates back to 1902 when the synthesis of methane from synthesis gas over a nickel catalyst was reported (17). In 1923, F. Fischer and H. Tropsch reported the formation of a mixture of organic compounds they called synthol by reaction of synthesis gas over alkalized iron turnings at 10—15 MPa (99—150 atm) and 400—450°C (18). This mixture contained mostly oxygenated compounds, but also contained a small amount of alkanes and alkenes. Further study of the reaction at 0.7 MPa (6.9 atm) revealed that low pressure favored olefinic and paraffinic hydrocarbons and minimized oxygenates, but at this pressure the reaction rate was very low. Because of their pioneering work on catalytic hydrocarbon synthesis, this class of reactions became known as the Fischer-Tropsch (FT) synthesis. 

Reactions of Synthesis Gas. The main hydrogen manufacturing processes produce synthesis gas, a mixture of H2 and CO. Synthesis gas can have a variety of H2-to-CO ratios, and the water gas shift reaction is used to reduce the CO level and produce additional hydrogen, or to adjust the H2 to-CO ratio to one more beneficial to subsequent processing (69) ... 

Synthesis gas is an important intermediate. The mixture of carbon monoxide and hydrogen is used for producing methanol. It is also used to synthesize a wide variety of hydrocarbons ranging from gases to naphtha to gas oil using Fischer Tropsch technology. This process may offer an alternative future route for obtaining olefins and chemicals. The hydroformylation reaction (Oxo synthesis) is based on the reaction of synthesis gas with olefins for the production of Oxo aldehydes and alcohols (Chapters 5, 7, and 8). 

Our ancestors made vinegar by aerobic bacterial fermentation of alcohol, which is derived from sugar, while it is now made by carbonylation of methanol, which is derived by reaction of synthesis gas, which is obtained by steam reforming of methane. 

Acetaldehyde is obtained from the reaction of synthesis gas with methanol, methyl ketals or methyl esters. The reactions are carried out with an iodide-promoted Co catalyst at 180-200 °C and 2000-5000 psig. In comparing the various feedstocks, the best overall process to make acetaldehyde involves the reductive carbonylation of methyl esters. In this case, acetaldehyde selec-tivities are > 95% ut acceptable rates and conversion. 

In 1925, Fischer and Tropsch developed a process for producing a mixture of saturated and unsaturated hydrocarbons, and oxygenated products such as alcohols and esters by the reaction of synthesis gas (a mixture of CO and H2) using heterogeneous catalysts of Fe and Co (eq. 1.1) [1],... 

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. 

Figure 6.18 illustrates the technique with a study on a proprietary cobalt on alumina Tropsch catalyst for Fischer-Tropsch synthesis (the reaction of synthesis gas, CO + Fl2, to hydrocarbon fuels) [55]. Trace amounts of platinum help to obtain an appreciable degree of reduction for the cobalt (similarly as in the temperature-programmed reduction of bimetallic Fe-Rh catalysts in Fig. 2.4). The left part of Figure 6.18 shows Co K-edge XANES of metal and oxide reference compounds, and illustrates the strong intensity of the white line region for ionic cobalt compounds. The XANES spectrum of the calcined CoPt/A Ch catalyst re-...

Wender, I., Reactions of Synthesis Gas, Fuel Proc. Technol., 48(3) (September 1996). 

The industrial scale reaction of synthesis gas to ammonia in pressure reactors takes place in a cyclic process in which the ammonia formed is removed from the reaction gas and the unreacted synthesis gas returned to the reactor. In addition to the ammonia formed, inert gases and the liberated reaction heat have to be continuously removed from the cyclic process. The excess heat of the product gas is used to heat the feed synthesis gas to the reaction temperature in a heat exchanger integrated into the reactor. Additional waste heat can be utilized for steam generation. The pressure loss in the synthesis gas due to its passage through the synthesis loop is compensated for and the fraction of synthesis gas converted replaced by fresh compressed synthesis gas ( fresh gas ). 

The activation of C-0 bond in carbon monoxide has been considered as a key step in Fischer-Tropsch synthesis in the reactions of synthesis gas [124]. 

Other Metals. - Isotopes have been widely used to study a number of the many catalytic reactions of synthesis gas. One of the most widely studied has been CO hydrogenation to produce methanol or higher carbon number alcohols. For example, C02 was employed to show that methanol was synthesized with the very active copper catalyst directly from CO2 and not from CO (e.g., see References 102-104). This literature is too vast to be included in this review. 

The overall reaction of synthesis gas over Rh and Rh-Mn catalysts, under the conditions of the experiments reported here, is represented in general terms by ... 

The conversion of biomass materials to high octane gasoline has been actively pursued for many years. Historically, methanol was made in very low yields by the destructive distillation of hardwoods. More recently, the manufacture of methanol has been by the reaction of synthesis gas over catalysts at high pressures. In theory, any carbon source can be used for this catalytic generation of methanol, but in practice, biomass has not been advantageous relative to coal or natural gas. Other approaches to making liquid fuel from biomass have involved the fermentation of biomass to ethanol in a rather slow process. The conversion of biomass to alcohols is technically feasible, but the utilization of the alcohols as transportation fuels will require modifications to the... 

Fuel cells with improved catalysts would allow the most efficient use of fossil fuels for the direct generation of electricity. There is major interest in the electrochemical reaction of synthesis gas or, better still, methane. It would be desirable to simultaeously generate energy and to produce valuable oxidation products in a fuel cell. Another interesting fuel is methanol, but technical reahzation has so far been unsuccessful because of the associated high activation energies. 

The reaction is catalyzed by Co carbonyls using reaction conditions in the range 200-250 bar and 175-210°C, and, when first reported, was characterized by both low yields (maximum 42%) and a spectrum of by-products including acetaldehyde, methyl formate, methyl acetate, propanol, butanol, and methane (17). Subsequently, catalytic activity toward hydrocarbonylation has been demonstrated with other metals, although Rh, usually appreciably more active than Co in other synthesis gas reactions, produces acids and esters, and ethanol only comprises a significant product at high H2 partial pressures. Methanol hydrocarbonylation may also be carried out with Fe or Ru catalysts promoted by tertiary amines, but the rates are even lower than with Co, which remains the preferred choice. The reaction rate is accelerated by the presence of promoters such as I , in which case acetaldehyde (which may also be obtained from the Co/I -catalyzed reaction of synthesis gas with methyl ketals or methyl esters (18)), comprises the major product. 

Table 15.1 Production from the reaction of synthesis gas over cobalt powders. 

---