CH4 formation

When one of the elements is solid, as in tire case of carbon in the calculation of the partial pressures of tire gaseous species in the reaction between methane and air, CO(g) can be used as a basic element together widr hydrogen and oxygen molecules, and thus the calculation of the final partial pressure of methane must be evaluated using the equilibrium constant for CH4 formation... 

The hydrogenation of CO and C02 on transition metal surfaces is a promising area for using NEMCA to affect rates and selectivities. In a recent study of C02 hydrogenation on Rh,59 where the products were mainly CH and CO, under atmospheric pressure and at temperatures 300 to 500°C it was found that CH4 formation is electrophobic (Fig. 8.54a) while CO formation is electrophilic (Fig. 8.54b). Enhancement factor A values up to 220 were... 

Figure 8.57. Effect of catalyst potential on the rates of formation of C2H6, C2H4) HzCO, CH3OH and CH3CHO during CO hydrogenation on Pd/YSZ. The rate of CH4 formation is of the order 10 9 mol/s and is only weakly affected by UWr Single pellet design P=12.5 bar, T=350°C. pH2/pco= -8, flowrate 85 cm3 STP/min.5 59...

CH4 formation decreases with increasing temperature and increases with increasing pressures. 

Reducing oxygen-to-steam ratio of reactant gases (or reactor inlet streams) increases H2 and CH4 formation, while increasing the oxygen-to-steam ratio will increase CO and C02 formation. 

Table III. Rate and Faradaic Efficiency of CH4 Formation from CH3OH at Electroplated Ru Electrodes a...

The addition of H2O and CO2 to the fuel gas modifies the equilibrium gas composition so that the formation of CH4 is not favored. Carbon deposition can be reduced by increasing the partial pressure of H2O in the gas stream. The measurements (20) on 10 cm x 10 cm cells at 650°C using simulated gasified coal GF-1 (38% H2/56% CO/6% CO2) at 10 atm showed that only a small amount of CH4 is formed. At open circuit, 1.4 vol% CH4 (dry gas basis) was detected, and at fuel utilizations of 50 to 85%, 1.2 to 0.5% CH4 was measured. The experiments with a high CO fuel gas (GF-1) at 10 atmospheres and humidified at 163°C showed no indication of carbon deposition in a subscale MCFC. These studies indicated that CH4 formation and carbon deposition at the anodes in an MCFC operating on coal-derived fuels can be controlled, and under these conditions, the side reactions would have little influence on power plant efficiency. 

The CO that is consumed in the process, besides forming hydrocarbons and C02 also caused the transformation of hematite to magnetite and subsequently the magnetite to iron carbide. Therefore, a better measure of Fischer-Tropsch synthesis (FTS) activity is the rate of CH4 formation plotted in Figure 28.1(b). It is seen that activation at 543 K makes the... 

The aim of this study is to convert as much as the hydrogen in the fuel into hydrogen gas while decreasing CO and CH4 formation. Process parameters of fuel preparation steps have been determined considering the limitations set by the catalysts and hydrocarbons involved. Lower S/C (steam to carbon) ratios favor soot and coke formation, which is not desired in catalytic steam and autothermal reforming processes. A considerably wide S/C ratio range has been selected to see the effect on hydrogen yield and CO formation. 

Finally, atom H detachment from the primary carbon atom causes C2H4 and C2H6 formation, whereas its detachment from the secondary carbon atom causes C3H6 and CH4 formation. Note that QH5 and CH radicals easily entrap H atoms from both positions. 

E. Vietzke, K. Flaskamp, V. Philipps Differences in the CH3 and CH4 formation from graphite under bombardment with hydrogen ions and hydrogen atoms/argon ions. J. Nucl. Mater. 128-129, 545 (1984)... 

Assuming BEP-type relationships to be valid, we can make a prediction of the selectivity of fhe Fischer-Tropsch reaction as a function of the M—C bond energy. In Figure 10, a schematic representation is given of the relative rates of production of particular groups of Fischer-Tropsch products as a function of fhe M—C interaction energy. Four types of reaction are compared coke or carbide formation, hydrocarbon chain growth, CH4 formation, and CO dissociation. 

Free energy changes (AG" ) and redox potentials ( " ) of partial reactions involved in CH4 formation... 

CH4 formation from H2/CO2 is dependent on Na ions [109,110]. Since CH4 formation from H2/CH3OH was found not to be dependent on Na ions, a role for this cation in the terminal part of the CO2 reduction pathway, namely CH3-S-C0M reduction to CH4, and in ATP synthesis could be excluded [111]. CH4 formation from H2/CH3OH involves three steps (i) binding of CH3OH to coenzymeM via two methyltransferases (see ref [13]) ... 

Heterodisulfide (CoM-S-S-HTP) reduction - coupled to primary translocation. The reaction in which ATP is synthesized during methanol reduction to CH4 could be identified with energetically competent membrane vesicles of the methanogenic strain G61. These vesicles, which are orientated more than 90% inside-out, catalyzed CH4 formation from CH3-S-C0M by reduction with H2 (Reactions 7,8) and coupled this process with the synthesis of ATP [112]. CH3-S-C0M reduction generated a ApH (inside acidic) as monitored by acridine dye quenching protonophores and ATP synthase inhibitors exerted their effects in accordance with a chemiosmotic type of ATP synthesis [113],... 

In the following subsections experiments are described which indicate that CO2 reduction to methylene-H4MPT is driven by a primary electrochemical Na potential generated by formaldehyde reduction to CH4. These experiments include (1) studies of the mode of energy transduction of the reverse reaction, the exergonic formaldehyde oxidation to CO2 and 2H2 (2) experiments on the effects of ionophores and inhibitors on CH4 formation from CO2/H2 and CH4 formation from formaldehyde/H2, and the determination of stoichiometries of primary Na" translocation. 

Stoichiometries of primary Na translocation. Further support for the conclusion that CO2 activation is driven by A/iNa" came from the determination of stoichiometries of primary Na transport coupled to CH4 formation from CO2/H2 and from formaldehyde/H2. Na" transport experiments were performed with whole cells of Methanosarcina barkeri equilibrated with Na the stoichiometry of Na export was... 

Perski et al. [109,110] found that growth and CFI4 formation from CO2 and H2 in various methanogens were dependent on Na ions. Subsequent studies [110] showed that CH4 formation from other substrates, methanol and acetate (see below), also requires Na ions. Thus a specific role of the cation in the coupling mechanism of ATP synthesis was envisaged. Later it was found that ATP synthesis driven by a potassium diffusion potential in Methanobacterium thermoautotrophicum was stimulated by Na [175]. However, a... 

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