Mixed Conducting Ceramics for Catalytic Membrane Processing

Liu, Yutie; Tan, Xiaoyao; Li, Kayiu

doi:10.1080/01614940600631348

Cited by 195 publications

(145 citation statements)

References 179 publications

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“…The stream velocity in typical opposed-flow diffusion flames is on the order of 10 -1~1 m/s [26,40], whereas that in the ITM reactor is limited by low oxygen permeation rates, which is on the order of 10 -1~1 μmol/cm 2 /s [20] or 10 -4~1 0 -3 m/s. Accordingly, the fuel stream must be fed to the sweep side at a low flow rate to satisfy the requisite stoichiometry and stabilize the reaction zone between the membrane and the sweep gas inlet.…”

Section: Reaction Environment Supported By An Itmmentioning

confidence: 99%

“…We note that an ITM requires high temperature for enabling substantial oxygen permeation to facilitate fuel conversion processes [20]. While a catalyst may contribute to fuel conversion typically at low temperature [21], in this high temperature regime, it has been demonstrated that the chemical reactions in the gas-phase dominate fuel conversion even if the surface catalytic reactions take place [22,23].…”

Section: Introductionmentioning

confidence: 99%

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Laminar oxy-fuel diffusion flame supported by an oxygen-permeable-ion-transport membrane

Hong

Kirchen

Ghoniem

2013

Combustion and Flame

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A numerical model with detailed gas-phase chemistry and transport was used to predict homogeneous fuel conversion processes and to capture the important features (e.g., the location, temperature, thickness and structure of a flame) of laminar oxy-fuel diffusion flames stabilized on the sweep side of an oxygen permeable ion transport membrane (ITM). We assume that the membrane surface is not catalytic to hydrocarbon or syngas oxidation. It has been demonstrated that an ITM can be used for hydrocarbon conversion with enhanced reaction selectivity such as oxy-fuel combustion for carbon capture technologies and syngas production. Within an ITM unit, the oxidizer flow rate, i.e., the oxygen permeation flux, is not a pre-determined quantity, since it depends on the oxygen partial pressures on the feed and sweep sides and the membrane temperature. Instead, it is influenced by the oxidation reactions that are also dependent on the oxygen permeation rate, the initial conditions of the sweep gas, i.e., the fuel concentration, flow rate and temperature, and the diluent. In oxy-fuel combustion applications, the sweep side is fuel-diluted with CO2, and the entire unit is preheated to achieve a high oxygen permeation flux. This study focuses on the flame structure under these conditions and specifically on the chemical effect of CO2 dilution. Results show that, when the fuel diluent is CO2, a diffusion flame with a lower temperature and a larger thickness is established in the vicinity of the membrane, in comparison with the case in which N2 is used as a diluent. Enhanced OH-driven reactions and suppressed H radical chemistry result in the formation of products with larger CO and H2O and smaller H2 concentrations. Moreover, radical concentrations are reduced due to the high CO2 fraction in the sweep gas. CO2 dilution reduces CH3 formation and slows down the formation of soot precursors, C2H2 and * Corresponding author. Tel.: +1 617 253 2295; Fax: +1 617 253 5981 Email address: ghoniem@mit.edu (Ahmed F. Ghoniem) 2 C2H4. The flame location impacts the species diffusion and heat transfer from the reaction zone towards the membrane, which affects the oxygen permeation rate and the flame temperature.

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Section: Reaction Environment Supported By An Itmmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Laminar oxy-fuel diffusion flame supported by an oxygen-permeable-ion-transport membrane

Hong

Kirchen

Ghoniem

2013

Combustion and Flame

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“…It can be assumed that the surface exchange reactions are no longer dependent on the concentration of electron holes. As a result, the backward reaction of surface exchange, expressed in (1), becomes pseudo-zero order at steady state under isothermal operations [45]. Then, based on the global reaction (1) and the reaction rate expression (2), the oxygen permeation rate by the surface exchange reaction on each side of the membrane can be expressed as, Depending on how the expressions in (3) and (4) are simplified or the reaction rate (2) is approximated, different empirical correlations for the surface exchange processes have been proposed [41,43,44,46].…”

Section: Surface Exchangementioning

confidence: 99%

“…Because these membranes are dense/gas-tight, direct permeation of gaseous oxygen molecules is prohibited, and only ionized oxygen can move across them. A number of different mechanisms have been discussed to explain bulk ion diffusion across an ITM, among which the vacancy transport mechanism is widely used [45].…”

Section: Bulk Diffusionmentioning

confidence: 99%

Numerical simulation of ion transport membrane reactors: Oxygen permeation and transport and fuel conversion

Hong

Kirchen

Ghoniem

2012

Journal of Membrane Science

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Ion transport membrane (ITM) based reactors have been suggested as a novel technology for several applications including fuel reforming and oxy-fuel combustion, which integrates air separation and fuel conversion while reducing complexity and the associated energy penalty. To utilize this technology more effectively, it is necessary to develop a better understanding of the fundamental processes of oxygen transport and fuel conversion in the immediate vicinity of the membrane. In this paper, a numerical model that spatially resolves the gas flow, transport and reactions is presented. The model incorporates detailed gas phase chemistry and transport. The model is used to express the oxygen permeation flux in terms of the oxygen concentrations at the membrane surface given data on the bulk concentration, which is necessary for cases when mass transfer limitations on the permeate side are important and for reactive flow modeling. The simulation results show the dependence of oxygen transport and fuel conversion on the geometry and flow parameters including the membrane temperature, feed and sweep gas flow, oxygen concentration in the feed and fuel concentration in the sweep gas.

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“…Over the past two decades, a number of mixed conducting materials based on perovskite-type oxides have been developed to meet many kinds of requirements in practical applications. Partial oxidation of natural gas to syngas in oxygen permeation membrane reactors attracts great interest of the industries due to the huge saving in capital costs and operating costs [10]. However, to realize the process, the membrane is required possessing both high permeation flux and stability under syngas atmosphere.…”

Section: Introductionmentioning

confidence: 99%