Effect of pressure on the oxidative coupling of methane in the absence of catalyst

Chen, Q.; Couwenberg, P. M.; Marin, Guy

doi:10.1002/aic.690400313

Cited by 54 publications

(66 citation statements)

References 29 publications

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“…Ethene is not detected at 1000 Pa since the formation also has to occur in the gas phase by involvement of dioxygen. The direct decomposition of ethyl radicals toward ethene can be ruled out at pressures of 1000 Pa (54). Hence, as a result of the low pressures the yield of C 2 products is less than 1% in the present study and the experimental data obtained with methane pulses will provide information on the generation of methyl radicals rather than on the global coupling reaction.…”

Section: Reaction Mechanismmentioning

confidence: 67%

An Investigation of the Oxygen Pathways in the Oxidative Coupling of Methane over MgO-Based Catalysts

Mallens

Hoebink

Marin

1996

Journal of Catalysis

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The oxidative coupling of methane to ethane and ethene has been investigated by admitting pulses of pure methane, pure oxygen, and mixtures of methane and oxygen to MgO, Li/MgO, and Sn/Li/MgO at temperatures ranging from 923 to 1073 K in a Temporal Analysis of Products (TAP) set-up. Moreover, pulses of oxygen followed by pulses of either methane, ethane, ethene, or carbon monoxide were applied to study the role of both adsorbed oxygen and surface lattice oxygen in the reaction mechanism.

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Section: Reaction Mechanismmentioning

confidence: 67%

An Investigation of the Oxygen Pathways in the Oxidative Coupling of Methane over MgO-Based Catalysts

Mallens

Hoebink

Marin

1996

Journal of Catalysis

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“…This phenomenon is related to the branched chain nature of the reaction mechanism [ 61 as will be shown using the model in Table 1. This model is based on the model from Chen et al [4] with some small modifications that allowed an adequate simulation of the experiments with cofeeding of ethane. It should be noted, however, that these modifications do not significantly alter the simulation results reported in [ 41.…”

Section: Methodsmentioning

confidence: 99%

The oxidative coupling of methane with cofeeding of ethane

1994

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The oxidative coupling of methane with cofeeding of ethane was investigated experimentally both in the absence and in the presence of a Sn/Li/MgO catalyst. Cofeeding ethane in the absence of catalyst results in a higher total radical concentration, explaining the strong increase of the observed feed conversions. The hydrogen-peroxy radical-concentration increase is more pronounced than the corresponding methyl radical concentration increase, resulting in a lower selectivity. The combined effect of feed conversion and selectivity is beneficial for inlet ethane-to-methane ratios lower than 4 mol%. Ethane cofeeding results in a slight increase of the oxygen conversion in the presence of a Sn/Li/ MgO catalyst. This can be accounted for by a mechanism in which both the hydrogen abstraction from the hydrocarbon and the regeneration of the active sites are kinetically significant. The corresponding decrease of methane conversion results from competition between methane and the more reactive ethane for these sites. The addition of ethane does not result in a beneficial effect on conversions to ethane or C2.

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“…The experimental reactor was designed such that mass-transport and mass-transfer limitations for the reactants and the products were negligible. The way of calculating the conversions, selectivities, and yields is similar to Chen et al (1994a).…”

Section: Methodsmentioning

confidence: 99%

“…The setup used for the kinetic experiments in this study has been described previously by Chen et al (1994a) for the measurement of the kinetics in the absence of catalyst. For the present study a continuousflow, sintered R-Al 2 O 3 tubular reactor with a length of 650 mm, an external diameter of 12 mm, and an internal diameter of 8 mm was used.…”

Section: Methodsmentioning

confidence: 99%

“…Hydrogen abstraction from ethene, reaction 4, is also considered possible even though the C-H bond in ethene is 5 kJ mol -1 stronger than that in methane. The hydrogen abstraction from ethane can be considered as a desired reaction since it leads to an ethyl radical, which mainly reacts further to ethene through the branched chain reactions in the gas phase; see Chen et al (1994a). Hydrogen abstraction from ethene is an undesired reaction because it leads to the vinyl radical, which is an important source of carbon monoxide in the gasphase reactions (Chen et al, 1994a).…”

Section: Kinetic Model Developmentmentioning

confidence: 99%

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Kinetics of a Gas-Phase Chain Reaction Catalyzed by a Solid: The Oxidative Coupling of Methane over Li/MgO-Based Catalysts

Couwenberg

Chen

Marin

1996

Ind. Eng. Chem. Res.

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A kinetic model was developed for the heterogeneously catalyzed oxidative coupling of methane for temperatures between 923 and 1023 K, inlet methane-to-oxygen ratios of 2 to 12, and oxygen conversions between 10 and 100%. This model features 10 catalytic reactions coupled to 39 gas-phase chain reactions and accounts for irreducible mass-transport limitations for reactive intermediates. The observed conversions and selectivities are adequately described up to 200 kPa total pressure. The observed strong increase of the conversions between 200 and 1000 kPa is described qualitatively. The catalyst not only produces radicals but also acts as an important radical quencher. Regeneration of the active sites through water desorption was found to be a kinetically significant step in the catalytic sequence producing methyl radicals. At atmospheric pressure approximately 90% of the methane and oxygen is converted on the surface of Sn/Li/MgO, the balance being converted through branched-chain reactions in the pores of the catalyst and in the interstitial phase. For Li/MgO only one-third of the methane is converted on the catalyst surface. For Sn/Li/MgO the catalytic oxidation of methyl radicals, rather than gas-phase reactions, limits the selectivity toward C2 products.

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Effect of pressure on the oxidative coupling of methane in the absence of catalyst

Cited by 54 publications

References 29 publications

An Investigation of the Oxygen Pathways in the Oxidative Coupling of Methane over MgO-Based Catalysts

An Investigation of the Oxygen Pathways in the Oxidative Coupling of Methane over MgO-Based Catalysts

The oxidative coupling of methane with cofeeding of ethane

Kinetics of a Gas-Phase Chain Reaction Catalyzed by a Solid: The Oxidative Coupling of Methane over Li/MgO-Based Catalysts

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