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High performance microchanneled asymmetric Gd Ce O -La Sr FeO -based membranes for oxygen separation #
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Shiyang Cheng, Hua Huang, Simona Ovtar, Søren Bredmose Simonsen, Ming Chen, Wei Zhang, Martin Søgaard, Andreas Kaiser, Peter Vang Hendriksen, and Chu-Sheng Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b10714 • Publication Date (Web): 01 Feb 2016 Downloaded from http://pubs.acs.org on February 8, 2016
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ACS Applied Materials & Interfaces
High Performance Microchanneled Asymmetric Gd0.1Ce0.9O1.95-δ-La0.6Sr0.4FeO3-δ -based Membranes for Oxygen Separation Shiyang Cheng*,†,∥, Hua Huang‡, Simona Ovtar†, Søren B. Simonsen†, Ming Chen†, Wei Zhang§, Martin Søgaard†, Andreas Kaiser†, Peter Vang Hendriksen†, Chusheng Chen‡ †
Department of Energy Conversion and Storage, Technical University of Denmark, Risø campus,
Frederiksborgvej 399, DK-4000 Roskilde, Denmark ‡
CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and
Engineering, University of Science and Technology of China, Hefei 230026, China §
Department of Materials Science and Key Laboratory of Mobile Materials MOE, Jilin
University, 130012 Changchun, China
ABSTRACT: A microchanneled asymmetric dual phase composite membrane of 70 vol.% Gd0.1Ce0.9O1.95-δ-30 vol.% La0.6Sr0.4FeO3-δ (CGO-LSF) was fabricated by a “one step” phaseinversion tape casting. The sample consists of a thin dense membrane (100 µm) and a porous substrate including “finger-like” microchannels. The oxygen permeation flux through the membrane with and without catalytic surface layers was investigated under a variety of oxygen
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partial pressure gradients. At 900 °C, the oxygen permeation flux of the bare membrane was 1.6 (STP) ml cm-2 min-1 for the air/He-case and 10.10 (STP) ml cm-2 min-1 for the air/CO-case. Oxygen flux measurements as well as electrical conductivity relaxation show that the oxygen flux through the bare membrane without catalyst is limited by the oxygen surface exchange. The surface exchange can be enhanced by introduction of catalyst on the membrane surface. An increase of the oxygen flux of ca. 1.49 (STP) ml cm-2 min-1 at 900 ºC was observed when catalyst is added for the air/He-case. Mass transfer polarization through the finger-like support was confirmed to be negligible, which benefits the overall performance. A stable flux of 7.00 (STP) ml cm-2 min-1 was observed between air/CO/CO2 over 200 hours at 850 °C. Partial surface decomposition was observed on the permeate side exposed to CO, in line with predictions from thermodynamic calculations. In a mixture of CO, CO2, H2 and H2O at similar oxygen activity the material will according to the calculation not decompose. The microchanneled asymmetric CGOLSF membranes show high oxygen permeability and chemical stability under a range of technologically relevant oxygen potential gradients.
KEYWORDS: phase inversion; dual phase composite membranes; electrical conductivity relaxation; surface exchange; mass transfer polarization; thermodynamic calculation
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ACS Applied Materials & Interfaces
1. Introduction Recently, oxygen transport membranes (OTMs) have been investigated for their potential use in supplying pure oxygen in different high temperature applications, such as high purity oxygen production 1, partial oxidation of methane for syngas production 2, oxy-fuel combustion biomass gasification
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. OTMs need to fulfil the following requirements for industrial
applications, i) provide a high oxygen flux, ii) have sufficient chemical stability under the relevant oxygen activities and temperatures, iii) be low cost, and iv) have high thermomechanical stability. Often these requirements are mutually contradicting; it is especially difficult to find a material that is both thermodynamically stable and provides high oxygen flux. Several materials belonging to the perovskite class; (A,B)MO3 (A=Rare earth, B=Ca, Sr, Ba, M=Fe, Co, Cu, Zn) have been shown to provide fast oxygen transport
5-11
. In particular with
respect to flux and oxygen surface exchange, BaxSr1-xCoyFe1-yO3-δ (BSCF) is one of the best performing materials 11-12. However, the chemical stability of such cobalt containing perovskites is insufficient for the low oxygen partial pressure applications (biomass gasification and syngas production)
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and the material is further unstable in CO2 15. Apart from decomposition under
reducing conditions, kinetic demixing arising from cation diffusion has also been reported to lead to the slow degradation of the oxygen flux
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. Most of the alkaline earth doped perovskites react
quickly with corrosive acidic gases, such as SO2 and H2S, which are the main gaseous impurities in flue gases
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. This is a serious material challenge for a membrane to be integrated with flue
gases. In addition to perovskite materials, fluorite-structured lanthanide doped ceria (Ln-doped ceria) has been studied for use in OTMs
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. These materials have excellent chemical stability, high
degree of mixed ionic and electronic conductivity under strongly reducing conditions and unique
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catalytic activity 18. These materials are particularly suitable for utilization in partial oxidation of methane 19 and for oxy-fuel combustion 20. It is noteworthy that the oxygen permeation flux of a 27-µm thick 10 at.% Gd-doped ceria (CGO) membrane exceeds 10 Nml cm-2 min-1 using air as the feed gas and wet hydrogen as the sweep gas at 850 °C 19, indicating an application potential in the chemical industry. However, the oxygen permeation flux of CGO-based membranes under a small oxygen potential gradient is low because of the low electronic conductivity under oxidizing conditions (
