Cocurrent membrane reactors vs. PFRs for shifting dehydrogenation equilibrium

Reo, Christopher M.; Bernstein, L. A.; Lund, C.R.F.

doi:10.1002/aic.690430222

Cited by 17 publications

(8 citation statements)

References 42 publications

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“…A high ammonia-to-methanol ratio is known to disfavor TMA production . In the first two cases the key to improved yields of MMA and DMA would be the selective removal of these components. , …”

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confidence: 99%

Preliminary Assessment of Membrane Reactors as a Means To Improve the Selectivity of Methylamine Synthesis

Sang¹,

Chang²,

Lund³

1999

Ind. Eng. Chem. Res.

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Methylamine synthesis from ammonia and methanol was studied using an amorphous silica−alumina catalyst. A combined thermodynamic and kinetic analysis shows that the selectivity ratio initially observed at high methanol conversion is a kinetic ratio, not a thermodynamic ratio. In some cases in the past this kinetic ratio has been taken to represent thermodynamic equilibrium. However, if the reaction is allowed to continue beyond the point where conversion of methanol and dimethyl ether is essentially complete, the product composition continues to change, albeit at a much lower rate. Eventually the thermodynamic selectivity ratio is obtained. A simple kinetic model was developed that captures this behavior, and this model was used to assess whether a membrane reactor might be used to alter the overall selectivity of methylamine synthesis. Four different membrane reactor configurations were considered. There were operational regimes where each configuration showed advantages, but these either occurred at low conversions or required extremely large reactors. These configurations are limited by currently available catalysts and membrane materials. The impact of membrane reactors could be increased with catalysts that retain high activity during methylamine disproportionation, i.e., after all methanol has been consumed. The development of membrane materials with better permselectivities would also increase the attractiveness of membrane reactor processes.

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confidence: 99%

Preliminary Assessment of Membrane Reactors as a Means To Improve the Selectivity of Methylamine Synthesis

Sang¹,

Chang²,

Lund³

1999

Ind. Eng. Chem. Res.

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“…Gobina et al (1995a) concluded that radial dispersion effects are negligible for the tube dimension used experimentally. Reo et al (1997), using mass-action kinetics, demonstrated that the yield of a porous membrane reactor offers little or no advantage over a diluted plug-flow reactor, and their simulations exhibit the existence of asymptotic solutions of the type analyzed here. Other studies considered adiabatic operation in which the transported hydrogen reacts with oxygen on the shell side to supply the necessary enthalpy; these studies will be reviewed later.…”

Section: Introductionmentioning

confidence: 75%

“…(Many other studies have defined a conversion based on the total olefin flow in the shell and tube side, and compared it with equilibrium values based on tube-side conditions. As recently noted by Reo et al (1997), such reactors offer no advantage over diluted PFRs). We simulated the reactor for a partially selective membrane, assuming that local equilibrium is maintained everywhere and that n ) 1 (eqs 1-2) and Q B ) Q C ) mQ H , where m is the selectivity parameter and the permeability difference between B and C is ignored.…”

Section: Df D(k′z)mentioning

confidence: 95%

Design of Membranal Dehydrogenation Reactors: The Fast Reaction Asymptote

Sheintuch

1998

Ind. Eng. Chem. Res.

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This study presents a systematic analysis of certain design aspects of a packed-bed catalytic membrane reactor for simple and fast dehydrogenation reactions. For sufficiently fast reactions, local chemical equilibrium can be assumed everywhere and conversion is transport limited. Under these assumptions, in a plug-flow isothermal reactor with a permselective membrane, analytical results can be derived showing the conversion dependence on reactor length and equilibrium coefficient. These results suggest that significant conversions should be expected in such a reactor with a reasonable membrane area-to-feed flow rate ratio (e.g., at 450 °C during butane dehydrogenation, with membrane flux of 1 cm 2 /cm 3 /min). High pressures lead to lower equilibrium conversions and to higher diffusive fluxes, resulting in a marginal change in overall conversion. Shell-side hydrogen partial pressure affects the conversion significantly, and the shell-to-tube flow rate ratio should be sufficiently large (10 to 100). Catalyst loading should be optimized to decrease length and improve selectivity. Ceramic Knudsen-selective membranes yield poor conversions. A preliminary analysis of an adiabatic reactor in which the diffusing hydrogen is combusted to supply the dehydrogenation enthalpy is also presented. These conclusions are contrasted with experimental observations obtained during isobutane dehydrogenation in a Pd membrane reactor.

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“…Ursachen sind u. a. die Tatsachen, dass ein erfolgreicher Einsatz eine genaue Abstimmung der Geschwindigkeiten der Reaktion und des Stofftransportes erfordert (¹kinetische Kompatibilitätª [52]) und dass die Steigerung des Umsatzes allein nicht immer eine ausreichende Rechtfertigung für den Einsatz eines komplizierteren Prozesses ist [53,54].…”

Section: Membranreaktorenunclassified

Zur Integration von Reaktion und Stofftrennung

Kienle

Sundmacher

Seidel‐Morgenstern

2005

Chemie Ingenieur Technik

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Auf Grund von unerwünschten Nebenreaktionen sowie thermodynamischen Limitierungen erfordert die Gewinnung reiner Produkte neben der Durchführung der chemischer Reaktionen stets den Einsatz von Stofftrennprozessen. Häufig erfolgt die Abtrennung der gewünschten Produkte sequentiell zum Reaktionsschritt in separat nachgeschalteten Trennapparaten. Eine attraktive und in den letzten Jahren zunehmend genutzte Möglichkeit besteht in der gezielten Integration eines Trennprozesses direkt in den Reaktor. Die verschiedenen Varianten unterscheiden sich insbesondere in der Art des eingesetzten Trennprozesses sowie in den angewendeten Betriebsweisen. Zielstellung dieser Arbeit ist es, an Hand von drei Beispielen bestehende Analogien zwischen verschiedenen integrierten Prozessen zu verdeutlichen. Betrachtet werden Reaktivdestillationskolonnen, Membranreaktoren und chromatographische Reaktoren. Anschließend werden die Grundzüge einer einheitlichen Theorie zur Analyse und raschen Bewertung integrierter chemischer Prozesse skizziert. Die Theorie basiert auf der Annahme chemischen Gleichgewichts. Sie verbindet das Konzept der transformierten Konzentrationsvariablen aus der Reaktivdestillation [27,30] mit der klassichen Gleichgewichtstheorie aus der Chromatographie [17,18]. Copyright © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [accessed February 8th 2013

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Cocurrent membrane reactors vs. PFRs for shifting dehydrogenation equilibrium

Cited by 17 publications

References 42 publications

Preliminary Assessment of Membrane Reactors as a Means To Improve the Selectivity of Methylamine Synthesis

Preliminary Assessment of Membrane Reactors as a Means To Improve the Selectivity of Methylamine Synthesis

Design of Membranal Dehydrogenation Reactors: The Fast Reaction Asymptote

Zur Integration von Reaktion und Stofftrennung

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