OCM in a fixed-bed reactor: limits and perspectives

Schweer, D.; Meeczko, L.; Baerns, M.

doi:10.1016/0920-5861(94)80157-6

Cited by 62 publications

(47 citation statements)

References 10 publications

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“…However, the selectivity of 35.1% at this point is significantly lower than the maximum selectivity of 64.8 % (T = 800 C, CH 4 /O 2 = 10). The predicted dependencies of methane conversion, C 2+ selectivity and yield on temperature and feed-gas composition are qualitatively the same as obtained in the polytropic fixedbed [2] and bubbling-bed reactor [5,31]. The highest yield of Y C2+ = 11.7% which was obtained at CH 4 /O 2 = 3 and T = 800 C is lower compared to the yields obtained in the laboratory-scale fixed-bed (Y C2+,max.…”

Section: Effect Of Reaction Temperature and Methane-to-oxygen Ratio Osupporting

confidence: 51%

“…This has been confirmed by experimental results obtained in laboratory-scale reactors. Whereas in polytropic fixed beds high temperature spikes limited the conversion of methane [2], in bubbling beds even for high conversions of methane (X CH4 < 35%) isothermal conditions were obtained [3±5] 1) . However, oxidative coupling of methane is a complex reaction; the reaction scheme contains parallel steps of methane to ethane and to nonselective products as well as several consecutive reactions.…”

Section: Introductionmentioning

confidence: 99%

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Reaction Engineering Simulations of Oxidative Coupling of Methane in a Circulating Fluidized-Bed Reactor

Pannek

Mleczko

1998

Chem. Eng. Technol.

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Oxidative coupling of methane in a circulating fluidized bed (ID = 1 m, H = 20 m) was investigated by means of reaction engineering modeling and simulations. The hydrodynamics of the catalytic bed was described applying a two-phase (core and annulus) and two-zone (acceleration and fully developed flow) model. Chemical reactions were described by two separate networks for the heterogeneous and homogeneous reactions. The one for the heterogeneous steps was developed for a La 2 O 3 / CaO catalyst. Concentration profiles revealed that due to the high activity of the catalyst, almost complete conversion of oxygen was already obtained in the acceleration zone. Reactor performance was found to be strongly influenced by mass transport limitation between the core and annulus and by gas-phase reactions. The maximum C 2+ yield of 13% (T = 800 C, X CH4 = 34.5%, S C2+ = 37.5%) was obtained at a high solids circulation rate (G s = 800 kg/m 2 s) and a low methane-to-oxygen ratio (CH 4 /O 2 = 3).The C 2+ yields in the CFB are comparable to the ones predicted for an industrial-scale bubbling-bed reactor.

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Section: Effect Of Reaction Temperature and Methane-to-oxygen Ratio Osupporting

confidence: 51%

Section: Introductionmentioning

confidence: 99%

Reaction Engineering Simulations of Oxidative Coupling of Methane in a Circulating Fluidized-Bed Reactor

Pannek

Mleczko

1998

Chem. Eng. Technol.

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“…For a better comparison with the kinetic data in the literature, the experimental condition for the OCM reaction were chosen similar to the reference work of Schweer et al. [20] The catalysts experience a strong deactivation with time on stream (TOS) until steady-state activity is reached (Fig. 2).…”

Section: Catalyst Deactivationmentioning

confidence: 99%

Structure sensitivity of the oxidative activation of methane over MgO model catalysts: I. Kinetic study

Schwach

Hamilton

Thum

et al. 2015

Journal of Catalysis

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The role of surface structure and defects in the oxidative coupling of methane (OCM) was studied over magnesium oxide as a model catalyst. Pure, nano-structured MgO catalysts with varying primary particle size, shape and specific surface area were prepared by sol–gel synthesis, oxidation of metallic magnesium, and hydrothermal post treatments. The initial activity of MgO in the OCM reaction is clearly structure-sensitive. Kinetic studies reveal the occurrence of two parallel reaction mechanisms and a change in the contribution of these pathways to the overall performance of the catalysts with time on stream. The initial performance of freshly calcined MgO is governed by a surface-mediated coupling mechanism involving direct electron transfer between methane and oxygen. The two molecules are weakly adsorbed at structural defects (steps) on the surface of MgO. The proposed mechanism is consistent with high methane conversion, a correlation between methane and oxygen consumption rates, and high C₂H₄ selectivity after short times on stream. The water formed in the OCM reaction causes sintering of the MgO particles and loss of active sites by degradation of structural defects, which is reflected in decreasing activity of MgO with time on stream. At the same time, gas-phase chemistry becomes more important, which includes the formation of ethane by coupling of methyl radicals formed at the surface and the partial oxidation of C₂H₆. The mechanistic concepts proposed in this work (Part I) will be substantiated in Part II by spectroscopic characterization of the catalysts (Schwach et al. [1])

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“…Another limitation to C2 yield is due to the ma@nmm oxygen concentration imposed by the explosive limit of CH4-02 mixtures [102] especially in the industrial process where the operation pressure is usually higher than in the lab-scale reactor and high dilution of the feed gas mixtures is unfavorable and causes more separation, cost . afterwards.…”

Section: Explosion Conditions Limiting Ocmmentioning

confidence: 99%

“…The distributed feed resulted in a marked increase of selectivityand yield. However, in another paper [102], it was claimed that, when the operation mode of distributed o~gen feed was applied, no improvement of Cz selectivity and yield compared to co-feed operation was achieved, and they concluded that the effectiveness of the distributed feed of oxygen depended mainly on -. -----, r ,, ..…”

Section: Introductionmentioning

confidence: 99%