NAMS 2002 Workshop - ICOM 2008

Inorganic Membranes II – 3
Thursday July 17, 10:00 AM-10:30 AM, O’ahu/Waialua
Carbonate-Ceramic Dual-Phase Membrane for High Temperature Carbon
Dioxide Separation
M. Anderson (Speaker), Arizona State University, Tempe, Arizona, USA
J. Lin, Arizona State University, Tempe, Arizona, USA - jerry.lin@asu.edu
Carbon dioxide is produced as a byproduct in many industrial processes, such as
the generation of electricity via coal combustion. Flue gas from conventional
coal-burning power plants contains roughly 13% carbon dioxide, 73% nitrogen,
10% water, 3% oxygen and less than 1% various pollutants. It is of increasing
importance to find ways to effectively separate carbon dioxide because it is a
known greenhouse gas. In this work we report the synthesis of a novel
carbonate-ceramic dual-phase membrane for improved high temperature carbon
dioxide separation. The dual-phase membrane is composed of a ceramic (solid)
phase, which acts as a support for a molten carbonate (liquid) phase.
La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-delta) (LSCF) was chosen as the support
material to take advantage of its mixed conductivity and improved oxidation
resistance in comparison to the previously used metallic dual-phase membrane.
LSCF supports were prepared by pressing and sintering powder synthesized
using the citrate method at 900 C. The pore radius of the sintered LSCF supports
was determined to be approximately 330 nm via both steady state helium
permeance and mercury porosimetry measurements. Dual-phase membranes
were successfully prepared by direct infiltration of molten carbonate at 520
degrees C. Helium permeances of the LSCF support before and after infiltration
were on the order of 10 -6 and 10 -10 mol/s.m 2 .Pa respectively, indicating that the
membrane was completely infiltrated. High temperature carbon dioxide
permeation experiments were performed from 650-900 C by feeding carbon
dioxide and argon on the upstream side of the membrane, and using helium as a
sweep gas on the downstream side of the membrane. It was observed that
LSCF’s relatively high oxygen ion conductivity made it possible for the support to
provide oxygen ions and facilitate formation of CO3 = in accordance with the
following reaction: CO2 + O = �� CO3 = . Upon reaching the downstream side of
the membrane, the reverse reaction occurs, leading to separation of pure carbon
dioxide. The LSCF dual-phase membrane exhibited a high carbon dioxide
permeance of 3.6x10 -8 mol/s.m 2 .Pa at 900 C. Additionally, the amount of argon
present in the permeate was found to be lower than the detection limit (~10 -10
mol/s.m 2 .Pa) of the gas chromatograph, indicating an ideal separation factor of
carbon dioxide over argon of at least 360. The activation energy for this
membrane was found to be 75 kJ/mol, which is comparable to the values for the
activation energy of oxygen vacancy diffusion in this particular material. This