Oxygen permeation and thermo-chemical stability of oxygen separation membrane materials for the oxyfuel process

The reduction of CO2 emissions, generally held to be one of the most significant contributors to global warming, is a major technological issue. CO2 Capture and Storage (CCS) techniques applied to large stationary sources such as coal-fired power plants could efficiently contribute to the global carbon mitigation effort. The oxyfuel process, which consists in the burning of coal in an oxygen-rich atmosphere to produce a flue gas highly concentrated in CO2, is a technology considered for zero CO2 emission coal-fired power plants. The production of this O2-rich combustion gas from air can be carried out using high purity oxygen separation membranes. Some of the most promising materials for this application are mixed ionic-electronic conducting (MIEC) materials with perovskite and K2NiF4 perovskite-related structures. The present work examines the selection of La0.58Sr0.4Co0.2Fe0.8O3-delta (LSCF58), La2NiO4+delta, Pr0.58Sr0.4Co0.2Fe0.8O3-delta (PSCF58) and Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF50) as membrane materials for the separation of O2 and N2 in the framework of the oxyfuel process with flue gas recycling. Annealing experiments were carried out on pellets exposed to CO2, water vapour, O2 and Cr2O3 in order to determine the thermo-chemical resistance to the atmospheres and the high temperature conditions present during membrane operation in a coal-fired power plant. The degradation of their microstructure was investigated using Scanning Electron Microscopy (SEM) in combination with electron dispersive spectroscopy (EDS) as well as X-Ray Diffraction (XRD). Also, the oxygen permeation fluxes of selected membranes were investigated as a function of temperature. The membrane materials selected were characterised using thermo-analytical techniques such as precision thermogravimetric analysis (TGA) and thermo mechanical analysis (TMA). An increase in thermal expansion and oxygen permeation associated with an increase in oxygen vacancy concentration, observed also in the TGA curves, occurs during heating. BSCF50 exhibits permeation fluxes well above those of LSCF58, PSCF58 and La2NiO4+delta, which are quite similar to each other. After exposure, no degradation of LSCF58, La2NiO4+delta and PSCF58 occurs. On the other hand BSCF50 is found to be unstable in CO2- and/or H2O-containing atmospheres and also to exhibit a chemical demixing. The thermo-chemical stability and the oxygen permeation performances are both crucial factors in the selection of high purity oxygen separation membranes for the oxyfuel process, thus making LSCF58, PSCF58 and La2NiO4+delta in this study the most suitable materials for this application. Serious issues arise, however, from the fact that secondary non-ion conducting oxide phases are formed in the bulk of every material, forming obstacles for oxygen ion migration, and also that a reaction with chromia occurs, preventing their use without protection.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2009

Author dc:creator

• Ellett, Anna Judith

Contributors dc:contributor

• Singheiser, Lorenz

• info:eu-repo/classification/ddc/620
• Perowskit
• Kohlenstoff
• Oxyfuel-Verfahren
• Membran
• Ingenieurwissenschaften
• Membranen
• Sauerstoffpermeation
• Oxyfuel-Prozess
• Kohlenstoff-Abscheidung
• Kohlenstoff-Speicherung
• oxygen permeation membranes
• perovskites
• oxyfuel process
• carbon dioxide capture

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113541%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A51229