Fuel methane, direct partial oxidation

Numerous studies have been published on catalyst material directly related to rich catalytic combustion for GTapplications [73]. However, most data are available on the catalytic partial oxidation of methane and light paraffins, which has been widely investigated as a novel route to H2 production for chemical and, mainly, energy-related applications (e.g. fuel cells). Two main types of catalysts have been studied and are reviewed below supported nickel, cobalt and iron catalysts and supported noble metal catalysts. 

The direct reaction of methane partial oxidation always competes with total oxidation reactions, which are also responsible for O2 consumption, whereas steam and dry reforming and C-forming reactions are also to be considered. All reactions are catalyzed by the materials which are active in partial oxidation, but different scales of reactivity for the catalysts can be estimated from the experimental data. Total oxidation prevails at the light-off of the fuel-rich stream over most catalysts, but precious metals are more active than transition metals. 

Methane reforming units receive methane-rich gas from a cryogenic product recovery facility and subject the gas to partial oxidation. Some of the carbon dioxide content is removed and the gas recycled to the reactors. Once liquids are recovered, the stream goes to essentially conventional refining units. The plant s production is primarily transport fuels. Most of the gasoline production is currently sold to other refineries for blending with their stocks, but a portion of the product is marketed directly to consumers. 

Finally, the study of reactions that facilitate a partial oxidation or oxidative reaction of methane using oxygen is an area of current active research motivated by the desire to discover technologies that convert methane directly to liquid fuels and higher value chemicals. 

Methane is a stable molecule and can typically be activated only at HT, e.g., above 650 °C in the steam reforming process. Recently, however. Spinner and Mustain (2012, 2013) have reported that methane could conceivably be activated in a room temperature carbonate fuel cell based on an AEM, and a novel catalyst that could produce the carbonate ion from O2 and CO2 at the cathode (Figure 15.33). The carbonate ion diffuses through the AEM and partially oxidizes methane at a NiO—Z1O2 composite anode catalyst to produce oxygenates such as formaldehyde and methanol with syngas. Such LT methane activation, if feasible, could allow the selective production of platform chemicals, rather than syngas, directly from natural gas. 

Other chemical routes for the direct conversion of methane into valuable chemicals, that is, CH3OH and HCHO, involve partial oxidation under specific reaction conditions [24-28]. As a general rule, these conversion processes use fuel-rich mixtures with the oxidant to minimize the extent of combustion reactions, which yield unwanted carbon oxides. Under these conditions, purely gas-phase oxidation reactions require high temperatures, which are detrimental for the control of selectivity of the desired products. Among the plethora of catalysts employed for this purpose, metal oxides — most of them transition metal oxides — are prominent. These catalyst systems are considered in this chapter. 

Mackie JC. Partial oxidation of methane the role of gas phase reaction. Catal Rev Sci Eng 1991 33 169. Edwards JH, Foster NR. The potential for methanol production from natural gas by direct catalytic partial oxidation. Fuel Sci Technol Int 1986 4 365—90. 

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