Lanthanum tungstate membranes for H-2 extraction and CO2 utilization: Fabrication strategies based on sequential tape casting and plasma-spray physical vapor deposition

[EN] In the context of energy conversion efficiency and decreasing greenhouse gas emissions from power generation and energy-intensive industries, membrane technologies for H-2 extraction and CO2 capture and utilization become pronouncedly important. Mixed protonic-electronic conducting ceramic membranes are hence attractive for the pre-combustion integrated gasification combined cycle, specifically in the water gas shift and H-2 separation process, and also for designing catalytic membrane reactors. This work presents the fabrication, microstructure and functional properties of Lanthanum tungstates (La28-xW4+xO54+delta, LaWO) asymmetric membranes supported on porous ceramic and porous metallic substrates fabricated by means of the sequential tape casting route and plasma spray-physical vapor deposition (PS-PVD). Pure LaWO and W site substituted LaWO were employed as membrane materials due to the promising combination of properties: appreciable mixed protonic-electronic conductivity at intermediate temperatures and reducing atmospheres, good sinterability and noticeable chemical stability under harsh operating conditions. As substrate materials porous LaWO (non-substituted), MgO and Crofer22APU stainless steel were used to support various LaWO membrane layers. The effect of fabrication parameters and material combinations on the assemblies' microstructure, LaWO phase formation and gas tightness of the functional layers was explored along with the related fabrication challenges for shaping LaWO layers with sufficient quality for further practical application. The two different fabrication strategies used in the present work allow for preparing all-ceramic and ceramic-metallic assemblies with LaWO membrane layers with thicknesses between 25 and 60 mu m and H-2 flux of ca. 0.4 ml/min cm(2) measured at 825 degrees C in 50 vol% H-2 in He dry feed and humid Ar sweep configuration. Such a performance is an exceptional achievement for the LaWO based H-2 separation membranes and it is well comparable with the H-2 flux reported for other newly developed dual phase cer-cer and cer-met membranes.ProtOMem Project under the BMBF grant 03SF0537 is gratefully acknowledged. Furthermore, the authors thank Ralf Laufs for his assistance in operating the PS-PVD facility. Dr. A. 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Ultrahigh oxygen permeation flux through supported Ba0.5Sr0.5Co0.8Fe0.2O3-delta membranes

[EN] Oxygen transport membranes made of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) were manufactured by tape casting and co-firing. The disk-shaped membranes consisted of a top gastight layer (70 mu m thick) and a porous substrate (830 mu m thick) with 34% open porosity. The variation of the permeation operation conditions allowed (i) the identification of the different limitations steps in the permeation process, i.e., bulk oxygen ion diffusion, catalytic surface exchange and gas phase diffusion in the membrane compartments and porous substrate, and (ii) the ultimate optimization of the oxygen flux. The variables considered in the systematic permeation study included the inlet gas flow rate of the sweep and air feed, the temperature and the nature of the oxygen feed gas (air or pure oxygen). Moreover, the influence of the deposition of a catalytic activation layer (17 mu m thick) made of BSCF on top of the thin gastight layer was investigated. As a result of this parametric study, unpreceded oxygen flux values were achieved, i.e., a maximum flux of 67.7 ml(STP) min(-1) cm(-2) was obtained at 1000 degrees C using pure oxygen as the feed and argon as the sweep, while a flux of 12.2 ml(STP) min(-1) cm(-2) at 1000 degrees C was obtained when air was used as the feed. (C) 2011 Elsevier BM. All rights reserved.Financial support from the Spanish Ministry for Science and Innovation (Project ENE2008-06302 and FPI Grant JAE-Pre 08-0058), EU through FP7 NASA-OTM Project (NMP3-SL-2009-228701), and the Helmholtz Association of German Research Centres through the Helmholtz Alliance MEM-BRAIN (Initiative and Networking Fund) is kindly acknowledged. Mrs H. Burlet has contributed to this work with the careful revision of the English language.Baumann, S.; Serra Alfaro, JM.; Lobera González, MP.; Escolástico Rozalén, S.; Schulze-Kueppers, F.; Meulenberg, WA. (2011). Ultrahigh oxygen permeation flux through supported Ba0.5Sr0.5Co0.8Fe0.2O3-delta membranes. Journal of Membrane Science. 377(1-2):198-205. https://doi.org/10.1016/j.memsci.2011.04.050S1982053771-

Promotion of mixed protonic–electronic transport in La5.4_{5.4}WO11.1−δ_{11.1− δ} membranes under H2_2S atmospheres

Catalytic membrane reactors (CMR) based on H$_2$-separation membranes can improve the performance of thermodynamically-limited reactions such as high-pressure steam methane reforming, ammonia cracking, non-oxidative aromatics production, and water gas shift reaction (WGS). In these industrial processes, the membrane surfaces are typically exposed to steam, CO$_2$, CO, H$_2$S, and hydrocarbons in combination with high temperatures. Therefore, the membrane materials require long-term thermo-chemical stability under the mentioned conditions. Stability in H$_2$S is of outstanding importance since its presence, even at ppm level, gives rise to substantial surface poisoning and decomposition of most materials. Here we characterize the influence of H$_2$S on the crystalline structure, lattice composition, and hydrogen-transport properties of La$_{5.4}$WO$_{11.1−δ}$, one of the reference protonic membrane materials. The incorporation of sulfide ions in the crystal lattice is ascertained from XRD, XPS, FESEM, WDS, EDS, and FIB-SIMS analyses. UV-vis spectroscopy and EIS measurements illustrate the effect of the incorporated sulfur in the transport properties, i.e., vigorously promoting the electronic conductivity mediated by the concurrent partial reduction of tungsten cations (W$^{6+}$). The rise in electronic conductivity allowed an H$_2$ flux of 0.042 mL cm$^{−2}$ min$^{−1}$ to be reached at 700 °C for a ∼700 μm-thick membrane, in contrast with negligible H$_2$ permeation in H$_2$S-free conditions

Catalytic activation of ceramic H2 membranes for CMR processes

[EN] The application of catalytic membrane reactors can overcome some of the disadvantages that reactions for the direct conversion of methane to fuels and petrochemicals present. Hydrogen separation membranes can shift the reaction equilibrium by hydrogen removal, improving the separation, selectivity and yield of the reactions. La5.5WO11.25-delta/La0.87Sr0.13CrO3-delta (LWO/LSC) based membranes present a high H-2 flux within the temperature range where CMR can be applied. However, the catalytic activity of the material is very low and it has to be improved. This work presents the development of different catalytic layers based on LSC material and the study of their influence on the H-2 flux obtained by using 60/40-LWO/LSC membranes. Membranes coated with porous layer made of Ni-infiltrated La0.75Ce0.1Sr0.15CrO3-delta exhibited the best permeation flux but still 20% lower than the one reached using Pt layers. Stability of the catalytic layers is also evaluated under H2 permeation conditions and under high steam content methane. (C) 2016 Elsevier B.V. All rights reserved.Financial support by the Spanish Government (Grants ENE2014-57651-R, CSD-2009-0050 and SEV-2012-0267) and CoorsTek Membrane Sciences is kindly acknowledged. The authors are indebted to M. Fabuel for sample preparation. The support of the Servicio de Microscopia Electronica of the Universidad Politecnica de Valencia is also acknowledged.Escolástico Rozalén, S.; Kjolseth, C.; Serra Alfaro, JM. (2016). Catalytic activation of ceramic H2 membranes for CMR processes. Journal of Membrane Science. 517:57-63. doi:10.1016/j.memsci.2016.06.017S576351

Phytostabilization of metals in mine soils using Brassica juncea in combination with organic amendments

Background and aims The high metal bioavailability and the poor conditions of mine soils yield a low plant biomass, limiting the application of phytoremediation techniques. A greenhouse experiment was performed to evaluate the effects of organic amendments on metal stabilization and the potential of Brassica juncea L. for phytostabilization in mine soils. Methods Plants were grown in pots filled with soils collected from two mine sites located in Central Spain mixed with 0, 30 and 60 tha?1 of pine bark compost and horse- and sheep-manure compost. Plant biomass and metal concentrations in roots and shoots were measured. Metal bioavailability was assessed using a rhizosphere-based method (rhizo), which consists of a mixture of low-molecular-weight organic acids to simulate root exudates. Results Manure reduced metal concentrations in shoots (10?50 % reduction of Cu and 40?80 % of Zn in comparison with non-amended soils), bioconcentration factor (10?50 % of Cu and 40?80 % of Zn) and metal bioavailability in soil (40?50 % of Cu and 10?30 % of Zn) due to the high pH and the contribution of organic matter. Manure improved soil fertility and was also able to increase plant biomass (5?20 times in shoots and 3?30 times in roots), which resulted in a greater amount of metals removed from soil and accumulated in roots (increase of 2?7 times of Cu and Zn). Plants grown in pine bark treatments and in non-amended soils showed a limited biomass and high metal concentrations in shoots. Conclusions The addition of manure could be effective for the stabilization of metals and for enhancing the phytostabilization ability of B. juncea in mine soils. In this study, this species resulted to be a potential candidate for phytostabilization in combination with manure, differing from previous results, in which B. juncea had been recognized as a phytoextraction plant

Design of periodic event-triggered control for polynomial systems: a delay system approach

Event-triggered control is a control strategy which allows the savings of communication resources in networked control systems. In this paper, we are interested in periodic event-triggering mechanisms in the sense that the triggering condition is only verified at predefined periodic sampling instants, which automatically ensures that Zeno behavior does not occur. We consider the case where both the output measurement and the control input are transmitted asynchronously using two independent triggering conditions. The developed result is dedicated to a class of nonlinear systems, where both the plant model and the feedback law can be described by polynomial functions. The overall problem is modeled and analyzed in the framework of time-delay systems, which allows to derive sum-of-squares (SOS) conditions to guarantee the global asymptotic stability in terms of the sampling period and the parameters of the triggering conditions. The approach is illustrated on a nonlinear numerical example

Towards upscaling of La5.5WO11.25-d manufacture for Plasma Spraying-Thin Film coated hydrogen permeable membranes

Lanthanum tungstate (La6WO12) is a promising material for the development of hydrogen separation membranes, proton ceramic electrolyzer cells and protonic ceramic fuel cells due to its interesting transport properties and stability under different operation conditions. In order to improve the hydrogen transport through the La6WO12 membranes, thin membranes should be manufactured. This work is based on the industrial production of La5.5WO11.25-¿ (LWO) powder by spray drying and the manufacturing of thin membranes by low-pressure plasma spraying (LPPS-TF) technique. LPPS-TF allows the production of dense thin films of high quality in an industrial scale. The powders produced by spray drying were morphological and electrochemically characterized. Hydrogen permeation fluxes of a membrane manufactured with these powders were evaluated and fluxes are similar to those reported previously for LWO powder produced in the lab scale. Finally, the transport properties of LWO thin films deposited on Al2O3 indicate that LPPS-TF produces high-quality LWO films with potential for integration in different applications.This work was financially supported by the European Union (DEMOYS Project, FP7/2007-2013-Grant Agreement 241309) and the Spanish Government (RTI2018-102161, SEV-2016-0683 and IJCI-2016-28330 grants)