Oxidation to synthesis gas

This reaction is in direct competition with the partial oxidation to synthesis gas, complete combustion, and carbon formation on the surface with the olefin essentially and intermediate en route to more stable products. Thermodynamic equilibrium calculations under these severe reaction conditions, predict the formation of carbon, CO, and H2, and only trace amounts of C2H4. Clearly, thermodynamic equilibrium is not obtained since the system is kinetically... 

The research on CFI4 conversion has recently focused on the direct oxidation to synthesis gas ... 

The combination of reactions (2) and (5) may be considered as a scheme for direct methane oxidation to synthesis gas (CO -f H2). Similar reactions may determine the high efficiency of mixed catalysts containing Ni and rare-earth oxides for the partial oxidation of methane to synthesis gas [9]. This mechanism does not require a preliminary total oxidation of methane followed by its reforming with CO2 and/or water which was considered as the main route for synthesis gas formation [10,11]... 

Hu, Y. and Ruckenstein, E. (1998). Broadened pulse-step change isotopic sharp pulse analysis of the mechanism of methane partial oxidation to synthesis gas, J. Phys. Chem. B, 102, pp. 230-233. 

Goula, M., Lemonidou, A., Gnmert, W., et al. (1996). Methane Partial Oxidation to Synthesis Gas Using Nickel on CaldumAluminate Catalysts, Catal. Today, 32, pp. 149-156. 

Methane. As our most abundant hydrocarbon, methane offers an attractive source of raw material for organic chemicals (see Hydrocarbons). Successful commercial processes of the 1990s are all based on the intermediate conversion to synthesis gas. An alternative one-step oxidation is potentially very attractive on the basis of simplicity and greater energy efficiency. However, such processes are not yet commercially viable (100). 

As an alternate to LNG, natural gas can be chemically converted to methanol, chemical feedstocks (such as ethylene), gasoline, or diesel fuel. Most processes start with the conversion of methane to synthesis gas, a mixture of carbon monoxide and hydrogen. This can be done partial oxidation, an exothermic reaction ... 

This XPS investigation of small iron Fischer-Tropsch catalysts before and after the pretreatment and exposure to synthesis gas has yielded the following information. Relatively mild reduction conditions (350 C, 2 atm, Hg) are sufficient to totally reduce surface oxide on iron to metallic iron. Upon exposure to synthesis gas, the metallic iron surface is converted to iron carbide. During this transformation, the catalytic response of the material increases and finally reaches steady state after the surface is fully carbided. The addition of a potassium promoter appears to accelerate the carbidation of the material and steady state reactivity is achieved somewhat earlier. In addition, the potassium promoter causes a build up on carbonaceous material on the surface of the catalysts which is best characterized as polymethylene. 

Partial oxidation of methane to synthesis gas over Ru/Ti02 catalysts... 

Concerning the reaction pathway, two routes have been proposed the sequence of total oxidation of methane, followed by reforming of the unconverted methane with CO2 and H2O (designated as indirect scheme), and the direct partial oxidation of methane to synthesis gas without the experience of CO2 and H2O as reaction intermediates. The results obtained by Schmidt and his co-workers [4, 5] indicate that the direct reaction scheme may be followed in a monolith reactor when an extremely short contact time is employed at temperatures in the neighborhood of 1000°C. However, the majority of previous studies over numerous types of catalysts show that the partial oxidation of methane follows the indirect reaction scheme, which is supported by the observation that a sharp temperature spike occurs near the entrance of the catalyst bed, and that essentially zero CO and H2 selectivity is obtained at low methane conversions (<25%) where oxygen is not fully consumed [2, 3]. A major problem encountered... 

Controlled elimination of mass and heat transport resistances is an important prerequisite for obtaining intrinsic kinetic parameters of the fast exothermic reaction of partial oxidation of methane to synthesis gas. It has been demonstrated that under conditions of strong transport limitations erroneous conclusions concerning the reaction scheme can be derived [7-9]. It was determined in this laboratory that transport limitations are practically absent over a wide range of operating conditions if one portion of the catalyst (< 40 pm) is diluted with -5 portions of an... 

The forty-eighth volume of Advances in Catalysis includes a description of a new and increasingly well understood class of catalysts (titanosilicates), a review of transmission electron microscopy and related methods applied to catalyst characterization, and summaries of the chemistry and processes of isobutane-alkene alkylation and partial oxidation and C02 reforming of methane to synthesis gas. 

Catalytic Conversion of Methane to Synthesis Gas by Partial Oxidation... 

The history of the development of methane conversion to synthesis gas is summarized as an introduction to the partial oxidation of methane, which is reviewed with emphasis on hot spots in reactors, major developments in the reduction of O2 separation costs, and reaction mechanisms. The various catalysts employed in CO2 reforming are examined, with emphasis on inhibition of carbon deposition. 2004 Elsevier Inc. 

Shen et al. (142) used an isotopic transient technique and XPS to investigate the partial oxidation of CH4 to synthesis gas on a Ni/Al203 catalyst at 973 K. The results show that CH4 can decompose easily and quickly to give H2 and Ni C on the reduced catalyst, and that Ni vC can react rapidly with NiO, formed by the oxidation of nickel by 02 to give CO or C02, depending on the relative concentration of Ni,C around NiO on the catalyst surface. The conclusion drawn by the authors (142) was not only that H2 and CO are primary products in the partial oxidation of CH4, but also that most of the CO2 is also the primary product of the surface reaction between Ni,C and NiO. In contrast, the kinetics results of Verykios et al. (143) indicated that the reaction on the Ni/La203 catalyst mainly takes place via the sequence of total oxidation to CO2 and H20, followed by... 

Using a temperature-programmed surface reaction (TPSR) technique, Li et al. (154) showed that this complete oxidation of methane took place on the NiO catalyst during the CHfOi reaction. Weng et al. (145) used in situ microprobe Raman and in situ time-resolved IR spectroscopies to obtain a relationship between the state of the catalyst and the reaction mechanism. These authors showed that RuC>2 in the Ru/SiC>2 catalyst formed easily at 873 K in the presence of a CH4/02/Ar (2/1/45, molar) mixture and that the dominant pathway to synthesis gas was by the sequence of total oxidation of CH4 followed by reforming of the unconverted CH4 by C02 and H20. Thus, these results indicate that the oxidation of methane takes place principally by the combustion mechanism on the oxidized form of this catalyst. 

Co and Fe catalysts have also been studied for the partial oxidation of methane to synthesis gas. Their potential relies on the fact that Co and Fe have higher melting and vaporizing points than Ni. Lower performances were mostly observed, however, which is probably related to the higher activity of CoO and FC2O3 for the complete oxidation of methane [121, 132, 133]. The recognized order of reactivity for partial oxidation is in fact Ni Co > Fe. However, it was observed that the performance of Co improves when a promoter is added. An extensive study of the catalytic partial oxidation of methane over CO/AI2O3 catalysts with different metals (0.1 wt% of Ni, Pt,... 

These values of A Hr are standard state enthalpies of reaction (aU gases in ideal-gas states) evaluated at 1 atm and 298 K. 7VU values of A are in kilojoules per mole of the first species in the equation. When A Hr is negative, the reaction hberates heat, and we say it is exothermic, while, when A Hr is positive, the reaction absorbs heat, and we say it is endothermic. Tks Table 2-2 indicates, some reactions such as isomerizations do not absorb or liberate much heat, while dehydrogenation reactions are fairly endothermic and oxidation reactions are fairly exothermic. Note, for example, that combustion or total oxidation of ethane is highly exothermic, while partial oxidation of methane to synthesis gas (CO + H2) or ethylene (C2H4) are only slightly exothermic. 

In this paper, we summarize results from a small scale methane direct oxidation reactor for residence times between lO and lO seconds. For this work, methane oxidation (using air or oxygen) was studied over Pt-10% Rh gauze catalysts and Pt- and Rh-coated foam and extruded monoliths at atmospheric pressure, and the reactor was operated autothermally rather than at thermostatically controlled catalyst temperatures. By comparing the steady-state performance of these different catalysts at such short contact times, tiie direct oxidation of methane to synthesis gas can be examined independent of the slower reforming reactions. 

From these experiments, one can see that the direct partial oxidation of CH4 to synthesis gas over catalytic monoliths is governed by a combination of transport and luetic effects, with the transport of gas phase species governed by the catalyst geometry and flow velocity and the lanetics determined by the nature of the catalyst and the reactor temperature. Under the conditions utilized here, the direct oxidation... 

We have shown that Cli can be oxidized directly to synthesis gas over a Pt or Rh monolith catalyst with surprisingly high selectivities for contact times of 10 to lO" s. Although these experiments do not give the equilibrium yields of H2 and CO reported in o Aer work at much longer residence times, they do show that both H2 and CO are primary products of the direct oxidation of CH4 over a noble metal catalyst. 

The current two-step industrial route for the synthesis of methanol, from coal or methane to synthesis gas and then from synthesis gas to methanol, has certain drawbacks. The economic viability of the whole process depends on the first step, which is highly endothermic. Thus a substantial amount of the carbon source is burned to provide the heat for the reaction. It would be highly desirable, therefore, to replace this technology with a technically simpler, single-step process. This could be the direct partial oxidation of methane to methanol, allowing an excellent way to utilize the vast natural-gas resources. Although various catalysts, some with reasonable selectivity, have been found to catalyze this reaction (see Sections 9.1.1 and 9.6.1), the very low methane conversion does not make this process economically feasible at present. 

It includes the steam reforming of methane over a nickel catalyst to synthesis gas followed by the copper-catalyzed transformation of the latter to methanol (see Section 3.5.1). Finally, formaldehyde is produced by oxidative dehydrogenation of methanol. 

Synthesis Gas. There are three principal routes to synthesis gas steam reforming, partial oxidation, and coal gasifica-... 

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