Synthesis gas formation

The catalytic partial oxidation of methane for the production of synthesis gas is an interesting alternative to steam reforming which is currently practiced in industry [1]. Significant research efforts have been exerted worldwide in recent years to develop a viable process based on the partial oxidation route [2-9]. This process would offer many advantages over steam reforming, namely (a) the formation of a suitable H2/CO ratio for use in the Fischer-Tropsch synthesis network, (b) the requirement of less energy input due to its exothermic nature, (c) high activity and selectivity for synthesis gas formation. 

Synthesis Gas Formation by Direct Oxidation of Methane over Monoliths... 

From the data shown in Fi re 1, two key points are evident (1) increasing the adiabatic reaction temperature increases the selectivity of synthesis gas formation, especially Sh2 and (2) Rh is a better catalyst than Pt for producing H2 by direct oxidation of CH4. 

D A. Hickman and L.D. Schmidt, Synthesis gas formation by direct oxidation of methane over monoliths. Symposium on Catalytic Selective Oxidation, Washington, DC, pp. 1263-1267 (1992). 

The production of synthesis gas from methane oxidation was also studied overFe catalyst in fuel cell using solid electrolyte (YSZ) at 850-950°C at atmospheric pressure [8]. The anodic electrode was Fe and the cathode that was exposed to air was Pt. Reduced iron was more active than oxidized iron for synthesis gas formation. The maximum CO selectivity and yield were nearly 100% and 73%, respectively. Carbon deposition was reported at high methane to oxygen ration. 

Three sets of experiments have been conducted. The first set is examining the influence of methane/oxygen ratios on the performance of the catalyst the second set is studying the effect of temperature on the synthesis gas formation and the third set is investigating the influence of residence time on synthesis gas selectivity and yield. The experimental data are shown in tables 1 and 2. Selectivity, yield and conversion are defined according to the following ... 

Fig. 5 shows the effect of various supports of nickel-loaded catalysts and reaction temperature on the methane conversion, in the partial oxidation of methane. At methane to oxygen ratio of 5 1, the maximum conversion of methane is 40 %, when reaction (5) proceeded, and 10% when complete oxidation proceeded. Only the oxidized diamond-supported Ni catalyst exceeded 10% conversion above 550 C, indicating that the synthesis gas formation proceeded. Ni-loaded LazOz catalyst afforded considerable methane conversion above 450 °C, but the product is mainly COz. Other supports to nickel showed no or only slight catalytic activity in the partial oxidation of methane. These results clearly show that oxidized diamond has excellent properties in the partial oxidation of methane at a low temperature, giving synthesis gas. Fig. 6 shows the effect of temperature on the product distribution, in the partial oxidation of methane. Above 550 °C, Hz and CO were produced, and below 500 °C, only complete oxidation occurred. The Hz to CO ratio should be 2 according to the stoichiometry. However, 3.2 and 2.8 were obtained at 550 and 600 °C, respectively. 

Among the cobalt containing perovskites GdCoO, SmCoO, NdCoO, PrCoO, and LaCoO, tested as catalyst precursors for the partial oxidation of methane the Gd-Co-0 system showed exceptionally better performance for synthesis gas formation (Figs. 6A-6C). At 1009 K a steady-state methane conversion of 73% with selectivities of 79 and 81% for CO and H., respectively, is observed for the catalyst Gd-Co-O. The catalysts Sm-Co-O and Nd-Co-0, of lower activity, show similar steady-state methane conversions in the temperature range studied. On the other hand, the H, and CO selectivities are much higher over Sm-Co-O. 

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]... 

Lai j SrxFe03-y (0oxidative dehydrogenation of ethane and isobutene. Yi et al. (1996) studied the former reaction and further investigated the phase diagram to verify a phase separation between La-rich and Sr-rich perovskites. They explored the 573-1073 K temperature region and reported that the maximum ethylene selectivity occurred at 923 K. At lower temperatures, CO2 predominates and at higher temperatures, cracking and synthesis gas formation occur. DTA and XRD indicate that a phase separation occurs between La-rich and Sr-rich perovskites. This separation was reflected in both the conductivity and catalytic activity. 

Figure 16.21 Synthesis gas formation by CPOM with N2O as oxygen source CH4 conversion (O) and CO selectivity Experimental details Flow...

Typical feedstock is natural gas, mainly CH4, although oil, coal and biomass can be used. The main route for synthesis gas formation is through steam reforming ... 

Recently, substantial research activity has been conducted in the area of CH4 conversion without the use of synthesis gas. We classify such processes as "Direct Methane Conversion." They have the potential of being more energy-efficient since they bypass the energy-intensive step of synthesis gas formation. 

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