Dense Ceramic Membrane Reactors Research Articles

Effects of membrane thickness and structural type on the hydrogen separation performance of oxygen-permeable membrane reactors

Membrane thickness and structural type, which are closely related to the species diffusion in the membrane bulk and reactions at the gas-solid interfaces, have important influences on the performance of a dense ceramic membrane. Recently, oxygen-permeable dense ceramic membrane reactors have been suggested for hydrogen purification at elevated temperatures. Mixed conducting composite with composition of 75 wt% Ce0.85Sm0.15O2-δ-25 wt% Sm0.6Sr0.4Al0.3Fe0.7O3-δ (SDC-SSAF) was fabricated into oxygen-permeable membranes with different thicknesses and structural types. The effects of membrane thickness and structural type on the hydrogen separation performance were tested under different hydrogen concentrations and flow rates on side I, different flow rates of steam/He mixed gas on side II as well as different temperatures. The effect of concentration polarization on hydrogen separation rate and the rate determining steps were discussed by comparing the performances of the symmetric membranes and the asymmetric membranes. The apparent activation energies of the membrane reactors for hydrogen separation were analyzed. This study will give some constructive guides to the subsequent work on how to effectively improve the hydrogen separation performance.

Autothermal reforming of ethanol in dense oxygen permeation membrane reactor

Perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) material was synthesized by the combined EDTA–citric acid complexing method and the disk-type BSCF dense membrane reactor (DMR) was constructed for H2 production by ethanol oxidative steam reforming reaction. The autothermal reaction conditions in the DMR were obtained through optimizing the ethanol oxidative steam reforming reaction (EOSR). The results showed that the hydrogen yield decreases (3.5–3.2mol/molEtOH) with the net heat of reaction Q decreases from 0 to −257J/molEtOH because the oxygen permeation flux for the membrane increases with temperature. The hydrogen production is 3.5mol/molEtOH at autothermal temperature of 750°C and the oxygen permeation flux of the dense ceramic membrane reactor is 6.5ml(STP)/cm2min. The activation energy for oxygen permeation was 46.4kJ/mol under the air/Ar gradient, as compared to about 20.1kJ/mol under EOSR reaction, respectively. The BSCF DMR performed stably under the autothermal reaction condition was stable for at least 180h. These results indicate the BSCF membrane holding the high oxygen permeation flux, the excellent phase reversibility and the good stability under the highly reducing atmosphere, shows great application potential for H2 production via the autothermal reaction.

ChemInform Abstract: Dense Ceramic Catalytic Membranes and Membrane Reactors for Energy and Environmental Applications

AbstractReview: 132 refs.

Dense ceramic catalytic membranes and membrane reactors for energy and environmental applications

Catalytic membrane reactors which carry out separation and reaction in a single unit are expected to be a promising approach to achieve green and sustainable chemistry with less energy consumption and lower pollution. This article presents a review of the recent progress of dense ceramic catalytic membranes and membrane reactors, and their potential applications in energy and environmental areas. A basic knowledge of catalytic membranes and membrane reactors is first introduced briefly, followed by a short discussion on the membrane materials including their structures, composition and strategies for material development. The configuration of catalytic membranes, the design of membrane reaction processes and the high temperature sealing are also discussed. The performance of catalytic membrane reactors for energy and environmental applications are summarized and typical catalytic membrane reaction processes are presented and discussed. Finally, current challenges and difficulties related to the industrialization of dense ceramic membrane reactors are addressed and possible future research is also outlined.

Performance study of heptane reforming in the dense ceramic membrane reactors

AbstractHeptane reforming was investigated in three dense ceramic membrane reactors, where the membranes were modified differently with reforming catalyst. Each reactor displayed distinctive catalytic behavior. The reactor with a bare membrane showed low catalytic activity and low oxygen permeation flux (JO2), but gave stable performance. The left two membranes reactors modified with catalyst both displayed shift processes at the preliminary stage of membrane reaction, not only in JO2 but also in the selectivity of all products. Moreover, the membrane reactor with more catalyst gave higher performance in the case of JO2 and CO selectivity. The observed shift phenomena are due to the activation of catalyst on the membrane surface, and the different amounts of catalyst produce different impaction on the membrane reactions. On the basis of the results in three membrane reactors, a reaction pathway of hydrocarbon reforming in dense ceramic membrane reactor is proposed. Being some different from combustion and reforming mechanism (CRR), hydrocarbon reforming in dense ceramic membrane reactor has its own characteristics. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Oxidative coupling of methane in dense ceramic membrane reactor with high yields

AbstractOxidative coupling of methane (OCM) was studied with dense tubular Bi1.5Y0.3Sm0.2O3 (BYS) membranes at various temperatures (870–930°C). BYS powders were synthesized by a citrate method. Tubular‐shaped dense membranes of BYS in the fluorite‐type FCC phase structure were fabricated by cold isostatic pressing with green machining. The best one‐pass C2 (C2H4 + C2H6) yield achieved for OCM in the BYS dead‐end membrane reactor was 35% at a C2 selectivity of 54% at 900°C. At the same C2 yield, the membrane reactor mode gives C2 selectivity of over 200% higher than the cofeed mode in the same membrane reactor under similar conditions. The oxygen permeation fluxes through tubular BYS membrane reactors under OCM reaction conditions are approximately 1.5 to 3.5 times higher than those under oxygen permeation conditions with He as the purge. After 6 days of OCM, BYS membrane remained in good integrity with minor phase segregation observed at the reaction side of the membrane.

Comparative Study on Oxygen Permeation and Oxidative Coupling of Methane on Disk-Shaped and Tubular Dense Ceramic Membrane Reactors

Oxygen permeation and oxidative coupling of methane (OCM) on fluorite-structured Bi1.5Y0.3Sm0.2O3-δ (BYS) membrane reactors of disk-shaped and tubular geometries were studied at high temperatures (800−900 °C). Their oxygen fluxes under an oxygen partial pressure gradient of air/helium are similar and in the range of (1−3) × 10-8 mol/cm2·s at 900 °C. The highest C2 yields obtained in the tubular and disk-shaped BYS membranes are 22% and 10.4%, respectively. The oxygen permeation fluxes through both the disk-shaped and tubular BYS membrane reactors under OCM reaction conditions are 1−2 orders of magnitude higher than those under oxygen permeation conditions with He as the purge. Oxygen permeation flux through the tubular BYS membrane is an order of magnitude smaller than that through the disk-shaped membrane under the OCM reaction conditions. The results show that the membrane geometry and downstream flow conditions have a significant effect on the reaction results. The tubular geometry gives more favorable results in terms of C2 yield and selectivity.

Maximizing H 2 production by combined partial oxidation of CH 4 and water gas shift reaction

A dense ceramic membrane reactor has been constructed to exclusively transport oxygen for the partial oxidation of methane (CH 4) to syngas (a mixture of CO and H 2) at temperatures of 850–900°C. H 2 production is enhanced in a second catalytic reactor through the water gas shift reaction, in which the CO reacts with steam that is injected into the reactor at a controlled rate to produce CO 2 and H 2. Experiments and thermodynamic calculations were used to establish the optimal lower temperature (≈400°C) and lower steam-to-CO ratio (≈2) to achieve thermodynamic efficiency while maximizing H 2 production. No unusual synergisms were observed by the combination of the two processes and the experimental results are in good agreement with thermodynamic predictions.