341 research outputs found
Manufacturing and Performance of supported BSCF-Membranes for oxygen separation
No full textManufacturing and Performance of supported BSCF-Membranes for oxygen separationNiehoff, P. (Corresponding Author)* ; Schulze-Küppers, F. * ; Baumann, S. * ; Vassen, R. * ; Buchkremer, H. P. * ; Meulenberg, W. A. *2015Wiley Interscience Hoboken, NJCeramic engineering and science proceedings 35(8), 325-335 (2015) G
High-Temperature Systems for a catalytic CO-Shift Membrane Reactor
No full textHigh-Temperature Systems for a catalytic CO-Shift MembraneReactorDésirée van Holt, Emanuel Forster , Wilhelm A. Meulenberg, Michael Müller, Mariya E.Ivanova, Stefan Baumann, Robert VaßenForschungszentrum Jülich, Institute of Energy and Climate Research, Leo-Brandt-Str., D-52425Juelich, Germanycorresponding author: [email protected] sequestration of CO2 via H2-selective, ceramic membranes in an IGCC-power plantis a highly interesting method, particularly for the high-temperature range of600 °C − 900 °C, due to the low efficiency losses that can be reached. It was shown thateven for this high-temperature range the utilization of a CO-shift catalyst leads to aconsiderable increase of the CO-conversion, at least up to 900 °C compared to anoperation mode without catalyst[1]. However, the harsh conditions of an IGCC-powerplant lead to very challenging operation conditions for the dense H2-selectivemembranes as well as for the CO-shift-catalysts.The present work aimed at the development of thermo-chemically and microstructurallystable, active and compatible membrane-catalyst systems for futurecatalytic CO-shift membrane-reactors. Therefore, the ceramic mixed protonic electronicconductors BaCe0.2Zr0.7Yb0.08Ni0.02O3−d and La5.5WO12−d were combined with ironbased catalysts like Fe/Cr/Cu-spinels. These materials were already studied intensivelyregarding the planned applications and show very good properties [2]. Additionally, formembrane-catalyst systems it is strongly required that the combined components donot influence each other negatively i.e. by diffusion or reaction.Figure: SEM picture of a cross section through a membrane-catalyst system of a 86Fe14Cr-catalyst on atape cast supported La5.5WO12−d-membrane after operation in a membrane reactor at 850 °C.The investigation identified material combinations that seem to be highly applicablefor future catalytic CO-shift membrane reactors in the high-temperature range up to900 °C. As shown in the figure above, the 86Fe14Cr-spinel catalyst and the La5.5WO12−d-membrane show very good compatibility. Additional investigations on membranereactorperformance, long term stability and scale up are necessary.[1] D. van Holt, Keramische Membranen für die H2-Abtrennung in CO-Shift-Reaktoren, DissertationRuhr-Universität Bochum 2014.[2] D. van Holt, E. Forster, M.E. Ivanova, W.A. Meulenberg, M. Müller, S. Baumann, R. Vaßen, Ceramicmaterials for H2 transport membranes applicable for gas separation under coal-gasification-relatedconditions, J. Eur. Ceram. Soc. 34 (2014) 2381 – 2389
Ceramic gas separation membranes or the use in CCUS
No full textCarbon Capture Utilization and Storage (CCUS) is an important strategy in order to mitigate greenhouse gas emissions enabling a circular economy. Since CO2 emissions typically occur at high temperature processes, ceramic gas separation membranes can provide the necessary separation and purification steps, which are key aspects in CCUS. The presentation introduces different types of ceramic membranes able to separate CO2, O2, H2 or other relevant gases from gas mixtures such as flue gases or synthesis gas. In particular membrane reactors are a promising option because of its energy efficiency enabling the combination of chemical reactions and gas separation (process intensification) [1]. The working principles are ionic transport (CO32-, O2-, H+) or molecular sieving in dense or porous membranes, respectively. State-of-the-art processing of membrane components as well as potential applications towards CCUS are described. To reach a high performance of the membrane systems thin film membranes, active surface layers and thermochemical and -mechanical stable supports with designed porosity are required. The production and characterization of membrane structures is explained using the example of sequentially tape cast and laminated supported membranes. References[1] W. Deibert, M.E. Ivanova, S. Baumann, O. Guillon, W.A. Meulenberg,Journal of Membrane Science 543 (2017) 79–9
Entwicklung glasbasierter Dichtungsmaterialien für das Fügen von Sauerstofftransportmembranen
No full textIn this thesis, different glass-based sealants were developed for joining oxygen transport membranes (OTM) to obtain matching the coefficient of thermal expansion (CTE) with membrane and support metals. The crystallization behavior of the BaO–CaO–SiO2–B2O3 system glass (H) and BaO–SrO–SiO2–B2O3 system glasses (BS) will be discussed. In addition, the glass-forming stability of glass matrices, filler type and amount effect on CTE, chemical compatibility, mechanical strength, shrinking behavior, viscous flow property, joining behavior, thermal cycling and long-term thermal stability were analyzed for various glass-based sealants. The feasibility of the fast joining process was also investigated to economize the energy costs of the heating process. SrTi0.75Fe0.25O3-δ (STF25) was used as an OTM, and the sealing partners were ferritic steel Aluchrom, pre-oxidized Aluchrom and Crofer22APU.BaO–CaO–SiO2–B2O3 system glass H matrix was first investigated with respect to its glass-forming tendency, crystallization and CTE. The crystalline behavior of glass H as the sealant matrix was investigated and predicted by experimental X-ray diffraction (XRD) analysis and the simulation using the thermodynamic package FactSage. Glass H exhibits a relatively low CTE (9.6 × 10-6 K-1) compared to STF25 and Aluchrom. Nine different filler materials were added to glass H in various amount for improving the CTE of glass-based composite sealants. Dilatometric tests were carried out to observe the influence of filler on thermal expansion. The viscous flow behavior of the composite sealant was investigated by hot stage microscopy (HSM) to determine the optimal joining temperature. The joining behavior of glass-based sealants for different thermal joining processes were analyzed via helium leakage testing, X-ray computed tomography (CT) inspection, scanning electron microscopy (SEM) analysis on cross-sections of the joints. The joints showed low helium leak rates smaller than 10-9 mbar·l·s-1 and good adherence of the glass sealants to the support metals and STF25. The mechanical shear strengths of sealants were measured by torsion testing on hourglass-shaped samples. A higher shear stress up to 62.2 MPa was found on composite joint which 40 wt.% Ag (HAg40) was added. HAg40 was able to withstand 20 times thermal cycles between room temperature and 800 °C and exhibited good thermal stability at 800 °C for up to 1500 h. These glass H-based sealants are promising candidates for OTMs.Three new BaO–SrO–SiO2–B2O3 (BS) glass sealants with different SrO contents (6-25 mol%) were developed for OTM joining applications. The strontium content was investigated in terms of its effect on the glass-forming tendency, thermal expansion, crystallization, shrinkage behavior, viscous flow, and joining behavior. The CTE value decreases with the increasing SrO content of the BS glasses. The glass with 15 mol% (BS15) SrO produced the best matching CTE (11.9 × 10-6 K-1) with STF25 and Aluchrom. The crystallization behavior of the BS glasses was investigated by XRD. Sinking dilatometric measurements simulated the joining procedure and observed the shrinkage behavior of the BS glasses. The viscous flow behavior of the BS glasses was investigated via HSM. The optimal joining temperature of the BS15 glass was chosen close at half-ball temperature. The sandwiched sample sealed by the BS15 glass achieved good gas-tightness with a low helium leak rate of < 10-9 mbar·l·s-1
Entwicklung glasbasierter Dichtungsmaterialien für das Fügen von Sauerstofftransportmembranen
No full textIn this thesis, different glass-based sealants were developed for joining oxygen transport membranes (OTM) to obtain matching the coefficient of thermal expansion (CTE) with membrane and support metals. The crystallization behavior of the BaO–CaO–SiO2–B2O3 system glass (H) and BaO–SrO–SiO2–B2O3 system glasses (BS) will be discussed. In addition, the glass-forming stability of glass matrices, filler type and amount effect on CTE, chemical compatibility, mechanical strength, shrinking behavior, viscous flow property, joining behavior, thermal cycling and long-term thermal stability were analyzed for various glass-based sealants. The feasibility of the fast joining process was also investigated to economize the energy costs of the heating process. SrTi0.75Fe0.25O3-δ (STF25) was used as an OTM, and the sealing partners were ferritic steel Aluchrom, pre-oxidized Aluchrom and Crofer22APU.BaO–CaO–SiO2–B2O3 system glass H matrix was first investigated with respect to its glass-forming tendency, crystallization and CTE. The crystalline behavior of glass H as the sealant matrix was investigated and predicted by experimental X-ray diffraction (XRD) analysis and the simulation using the thermodynamic package FactSage. Glass H exhibits a relatively low CTE (9.6 × 10-6 K-1) compared to STF25 and Aluchrom. Nine different filler materials were added to glass H in various amount for improving the CTE of glass-based composite sealants. Dilatometric tests were carried out to observe the influence of filler on thermal expansion. The viscous flow behavior of the composite sealant was investigated by hot stage microscopy (HSM) to determine the optimal joining temperature. The joining behavior of glass-based sealants for different thermal joining processes were analyzed via helium leakage testing, X-ray computed tomography (CT) inspection, scanning electron microscopy (SEM) analysis on cross-sections of the joints. The joints showed low helium leak rates smaller than 10-9 mbar·l·s-1 and good adherence of the glass sealants to the support metals and STF25. The mechanical shear strengths of sealants were measured by torsion testing on hourglass-shaped samples. A higher shear stress up to 62.2 MPa was found on composite joint which 40 wt.% Ag (HAg40) was added. HAg40 was able to withstand 20 times thermal cycles between room temperature and 800 °C and exhibited good thermal stability at 800 °C for up to 1500 h. These glass H-based sealants are promising candidates for OTMs. Three new BaO–SrO–SiO2–B2O3 (BS) glass sealants with different SrO contents (6-25 mol%) were developed for OTM joining applications. The strontium content was investigated in terms of its effect on the glass-forming tendency, thermal expansion, crystallization, shrinkage behavior, viscous flow, and joining behavior. The CTE value decreases with the increasing SrO content of the BS glasses. The glass with 15 mol% (BS15) SrO produced the best matching CTE (11.9 × 10-6 K-1) with STF25 and Aluchrom. The crystallization behavior of the BS glasses was investigated by XRD. Sinking dilatometric measurements simulated the joining procedure and observed the shrinkage behavior of the BS glasses. The viscous flow behavior of the BS glasses was investigated via HSM. The optimal joining temperature of the BS15 glass was chosen close at half-ball temperature. The sandwiched sample sealed by the BS15 glass achieved good gas-tightness with a low helium leak rate of < 10-9 mbar·l·s-1
Einfluss der Herstellungsbedingungen auf die mechanische Stabilität asymmetrischer BSCF-Membranen für die Sauerstoff-Bereitstellung
No full textSauerstoff – O2 wird in vielen Industriebranchen zur Prozessintensivierung genutzt. In Verbrennungsprozesses ermöglicht sein Einsatz z.B. die Einsparung von Brennstoff, die Senkung der CO2- und NO2-Emissionen und eine hocheffiziente Abtrennung von CO2. Kommerzielle O2-Produktionsverfahren sind energieintensiv, z.T. ist ein aufwändiger Transport zum Endkunde nötig. Gemischt leitende keramische MIEC-Membranen (Mixed Ionic Electronic Conductor) ermöglichen eine energieeffizientere Erzeugung von reinem O2 vor Ort. Die hohen Investitionskosten stellen ein Markteintrittshemmnis dar, dass durch Verringerung der Membrandicke bzw. eine Steigerung der O2-Permeation abgesenkt werden könnte. Dafür müssen jedoch die geringe mechanische Festigkeit und Ausfallsicherheit der BSCF-Rohrmembranen (BSCF – Ba0,5Sr0,5Co0,8Fe0,2O3-δ) durch einen optimierten Herstellungsprozess deutlich erhöht werden. Die merkliche Verbesserung dieser Eigenschaften im Rahmen einer optimierten Herstellung war das Ziel der vorliegenden Arbeit. Dabei bildete der auf vielen Jahren intensiver Forschung basierende Stand der Technik am Fraunhofer IKTS neben ausführlichen Recherchen zum technischen Stand anderer Forschungsgruppen das Fundament, auf dem grundlegende Zielstellungen formuliert und Versuchspläne erstellt wurden. Da die Festigkeit keramischer Bauteile entscheidend vom keramischen Gefüge beeinflusst wird, wurde der Einfluss der Pulvermorphologie und der Sinterbedingungen auf Schwindung, Gefügekorngröße, Porosität und Bruchfestigkeit untersucht. Dazu wurden zunächst BSCF-Pulver mit unterschiedlicher Korngrößenverteilung präpariert und durch Trockenpressen zu Presslingen verarbeitet. Bei der anschließenden Sinterung unter unterschiedlichen Bedingungen konnte bereits 130 K unterhalb der üblichen Sintertemperatur eine vergleichbare Verdichtung erreicht werden, während sich die Gefügekorngröße deutlich verringerte. Durch den Zusatz von Fremdoxiden konnte die Gefügekorngröße ebenfalls deutlich verringert werden. Insgesamt wurde eine Verringerung der Gefügekorngröße um bis zu 80 % erreicht. Im Gegensatz zu den Erwartungen hatte dies jedoch keine Festigkeitssteigerung zur Folge. Sogenannte asymmetrische Rohrmembranen bestehen aus einen offenporigen Trägerrohr, das typischerweise im Grünzustand mit einer porenfreien Trennschicht beschichtet und gesintert wird. Die Trägerrohre wurden in dieser Arbeit durch Extrusion eines wässrig plastifizierten Versatzes unter Zugabe von Porenbildnern hergestellt. Dabei wurden die Menge des zugegebenen Porenbildners, die Knetdauer der Extrusionsmischung und die Drehzahl der Extrusionsschnecke in einem weiten Bereich variiert. Es zeigte sich überraschend, dass der Porenanteil nahe der Oberfläche der Extrudate sehr viel geringer war als im Volumen. Darüber hinaus wurde an den Oberflächen nahezu die doppelte Gefügekorngröße im Vergleich zur Gefügekorngröße im Volumen des porösen Materials bestimmt. Letztere war außerdem deutlich geringer als bei den unter vergleichbaren Bedingen gesinterten porenarmen Tabletten und verringerte sich mit steigendem Porengehalt. Dies ist nur durch einen stark hemmenden Einfluss der offenen Poren auf das Kornwachstum bzw. die Korngrenzenwanderung zu erklären. Durch sukzessive Variation der Herstellungsbedingungen gelang es, unter Erhalt der offenen Porosität die Festigkeit der Trägerrohre um bis zu 30 % zu steigern und das Weibull-Modul zu erhöhen. Durch parallele Änderung der Sinterbedingungen konnte außerdem die Gefügekorngröße deutlich abgesenkt werden. Die Analyse der linearen Schwindungsanteile in verschiedenen Richtungen ergab sowohl bei gepressten als auch bei extrudierten Proben eine starke Abweichung des erwarteten Verhältnisfaktors von 3 zwischen volumetrischer und linearer Sinterschwindung mit zunehmender Volumenschwindung. Die O2-Permeation der unter optimierten Bedingungen hergestellten asymmetrischen Membranen erwies sich bei hohen Betriebstemperaturen im Vergleich zu den Referenzproben als geringer, bei niedriger Temperatur hingegen als höher. Als Ursachen sind die geringere Gefügekorngröße in den Trennschichten sowie eine offensichtlich etwas geringere thermische Aktivierungsenergie anzusehen. Bei der 25-wöchigen Langzeit-Auslagerung von BSCF-Membranträgern wurde für Proben mit geringer Ausgangskorngröße ein merkliches Kornwachstum festgestellt, während Proben mit von vorherein höherer Gefügekorngröße kein Kornwachstum zeigten. Im letzteren Fall kam es durch das ausbleibende Kornwachstum während der Auslagerung zu einer Umformung der Porenstruktur die mit einer Festigkeitsabnahme um ca. 35 % bezüglich des Ausgangswertes einherging. Dies wurde als kritisch für den weiteren Betrieb eingeschätzt. Die Proben mit geringerer Gefügekorngröße zeigten zwar keinen bzw. nur einen geringen Festigkeitsverlust, wiesen jedoch zu Beginn der Auslagerung eine stärkere makroskopische Verformung als Proben mit hoher Gefügekorngröße auf. Diese Verformung nahm jedoch mit zunehmender Auslagerungsdauer bzw. mit zunehmender Korngröße ab. Insgesamt ergibt sich somit ein optimiertes Herstellungsverfahren, aus dem Trägerrohre mit deutlich verringerter Gefügekorngröße und erhöhter Festigkeit hervorgehen. Auch bei halbjähriger Auslagerung bei Betriebstemperatur ergibt sich kein merklicher Festigkeitsabfall, wodurch sich eine wesentlich verlängerte Nutzungsdauer erwarten lassen. Zudem ist die übergreifende Anwendung der gewonnen Ergebnisse z.B. bei der Herstellung monolithischer BSCF-Membranen durchaus denkbar.Oxygen – O2 is widely used for process intensification in various industrial sectors. Its application in combustion processes enables saving of fuel, reduction of CO2 and NO2 emissions as well as a highly efficient separation of CO2. Conventional processes for O2-production appear to be energy-intensive and are related to sophisticated transport conditions for customers. In contrast, the use of mixed conducting ceramic MIEC membranes (Mixed Ionic Electronic Conductor) enables a more efficient local production of oxygen with high chemical purity. Market entrance is generally hindered by high investment costs which could be lowered by reduction of membrane thickness and increasing oxygen permeation. Therefore, an optimized membrane production is required in order to sharply increase the presently low mechanical stability and to sharply decrease the presently high failure probability. The aim of the present work was to distinctly improve mechanical membrane properties by adjusting preparation conditions. General objectives and experimental setups were mainly based on the state of the art relating asymmetric membrane production at Fraunhofer IKTS and research from other scientific groups working within this field. Because mechanical strength of ceramic components is mainly influenced due to the ceramic structure the impact of powder morphology and sintering conditions on shrinkage, grain size within the ceramic structure, porosity and fracture strength was investigated. Therefore, BSCF powders with varying particle size distributions were prepared and used for fabrication of disc-shaped pellets by dry pressing. Due to variation of sintering temperature and duration it was noticed that high densification could be still reached after reduction of the usual firing temperature by 130 K while grain size was significantly lowered. Another distinct reduction of grain size was reached by adding foreign oxides to the BSCF powders. Altogether, the grain size of the BSCF pellets was reduced by up to 80 % in relation to reference grain size by variation of powder morphology and sintering conditions. In contrary to expectations this wasn’t entailed by an increase of fracture strength. Tubular asymmetric membranes consist of a porous support tube and a dense separation layer. The porous support is typically coated in green state whereupon the membrane is finished in a co-firing process. In the present work the support tubes were prepared by wet stiff-plastic extrusion of a viscous mixture containing BSCF powder and organic additives such as pore formers. Varying amount of pore forming agent was added to the mixture and kneading time of the mixture and rotational speed of the extrusion screw were adjusted in a broad range. Surprisingly, surface porosity of the extruded samples appeared to be much lower compared to bulk porosity. In addition, surface grain size was found to be almost twice as large compared to bulk grain size of the porous supports. Furthermore, bulk grain size of the extruded samples was significantly lower than grain size of pellets prepared using comparable sintering conditions and decreased with rising pore content. These effects are related to a strong inhibiting effect on grain growth and grain boundary movement caused by the open pore network. Systematic variation of fabrication parameters resulted in increased fracture strength of the porous supports by almost 30 % and increased Weibull modulus while open porosity was nearly unaffected. In addition, grain size was distinctly lowered by simultaneous adjustment of sintering conditions. Investigation of linear shrinkage for pellets and extruded samples revealed that the ratio of 3:1 typically assumed for volumetric and linear shrinkage of ceramic components is not valid for increased volume shrinkage as present during sintering. O2-Permeation of asymmetric membranes prepared based on optimized manufacturing conditions was lower compared to O2-permeation of membranes taken as a reference at high operation temperatures. In contrast, low temperature O2-permeation appeared to be higher. Reduced grain sizes within the ceramic structure of the separation layers and a slightly lowered thermal activation energy are considered to be the main reasons for the observed effects. Thermal long-term treatment of BSCF membrane supports for 25 weeks resulted in distinct grain growth for samples with low initial grain size while no grain growth was observed for samples with large initial grain size. The absence of grain growth during thermal long-term treatment was entailed by deformation of the open pore network and a loss of fracture strength by almost 35 % compared to fracture strength after firing which was considered to be critical for further operation. No or only slight loss of fracture strength was found for supports with low initial grain sizes but increased macroscopic deformation was observed in the first stages of the long-term treatment. The deformation was found to decrease with increasing time of treatment in relation to increasing grain size. Altogether, an optimization of the fabrication process for tubular asymmetric BSCF membranes was received which enables production of membrane supports with distinctly lowered grain size and increased mechanical strength. In addition, long-term treatment at operation temperature for at least half of a year does not result in critical loss of fracture strength which is why a considerably elongated operating life can be also expected. Furthermore, comprehensive use of the results received from the present work i.e. for manufacturing of monolithic BSCF membranes seems to be promising
Einfluss der Herstellungsbedingungen auf die mechanische Stabilität asymmetrischer BSCF-Membranen für die Sauerstoff-Bereitstellung
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Development of asymmetric dual phase composite oxygen transport membranes
No full textDEVELOPMENT OF ASYMMETRIC DUAL PHASE COMPOSITE OXYGEN TRANSPORT MEMBRANESFalk Schulze-Küppers 1 – Stefan Baumann 1 – Madhumidha Ramasamy 1– Wilhelm A. Meulenberg 11 Forschungszentrum Jülich, Institute of Energy and Climate Research, D-52425 Juelich, Germany, e-mail: [email protected]: Oxygen Transport Membrane, Cer-Cer Dual Phase, asymmetric Membrane, Tape castingMixed Ionic electronic conductors (MIEC) are potential candidates for various applications including oxygen transport membranes (OTM) due to their high efficiency and infinite selectivity towards oxygen at elevated temperatures [1]. Possible applications for OTM are supply of highly pure oxygen or membrane reactors, in which the separated oxygen is directly utilized to form valuable products such as synthetic fuels or bulk chemicals. OTM transport oxygen ions by solid state diffusion through oxygen vacancies, which cannot be occupied by other ions. However, the transport is based on lattice defects and, thus, high-performance OTM materials mainly perovskites (with high defect density and mobility) suffer from limited stability in application conditions with potentially reducing and/or acidic gas atmospheres (requiring low defect density and mobility). One approach to face the trade-off between chemical stability and oxygen flux performance are dual phase composites. In such cer-cer composites two phases are coupled to provide pure electronic and ionic conducting pathway, respectively. In this work, composites of 20 mol% Gadolinia doped ceria (GDC) as ionic conductor and FeCo2O4 spinel (FCO) as electronic conductor are investigated [2]. GDC-FCO ratio is varied proving that spinel content as low as 10 wt-% is sufficient to ensure oxygen permeability, although well below the percolation threshold. In addition, the influence of the powder synthesis route on microstructure and corresponding oxygen permeation properties is investigated and compared to state-of-the-art single phase material, i.e. La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF). In order to increase oxygen flux further, by microstructural optimization of the membrane layout, asymmetric membranes were manufactured by sequential tape casting. Such membranes consist of a thin (~15 µm), dense membrane layer and a porous support porosity (>40 %) for mechanical stability. An important issue in tape casting is the used raw materials. In order to realize cost efficient manufacturing, a reactive sintering of the membranes was developed, using commercially available CGO, Fe- and Co-oxides as raw material. Oxygen flux in such membranes is clearly limited by surface exchange, due to the low electrochemically active triple phase boundary length, at which oxygen exchange takes place. The performances of bulk and asymmetric membranes are analysed and the potential of this type of materials is discussed with regard to microstructural optimization.References1. J. Sunarso, et. al. “Mixed ionic–electronic conducting (MIEC) ceramic-based membranes for oxygen separation”, J. Mem. Sci., 320, pp.13-41, 20082. M. Ramasamy, et al. “Influence of Microstructure and Surface Activation of Dual-Phase Membrane Ce0.8Gd0.2O2 - FeCo2O4 on Oxygen Permeation” J. Am. Ceram. Soc., 99, pp.349–355, 201
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