NAMS 2002 Workshop - ICOM 2008

Facilitated Transport Membranes – 1 – Keynote
Friday July 18, 9:30 AM-10:15 AM, Wai’anae
Facilitated Transport Membrane for Selective Separation of CO2 from CO2-
H2 Mixtures at Elevated Temperatures and Pressures
R. Yegani, Kobe University, Kobe, Japan
M. Teramoto (Speaker), Kobe University, Kobe, Japan
O. Okada, Renaissance Energy Research Company, Osaka, Japan
H. Matsuyama, Kobe University, Kobe, Japan - matuyama@kobe-u.ac.jp
A novel facilitated transport membrane consisting of Cs2CO3 as CO2 carrier and
poly (vinyl alcohol)/ poly (acrylic acid) gel (PVA/PAA gel) as support was
developed for the removal of CO2 from CO2/H2 mixtures at relatively high
pressures (up to 600kPa) and temperatures (125 - 200°C). For this membrane,
the presence of water in the membrane is indispensable for the CO2-carrier
reaction (overall reaction: CO2 + CO3 2- + H2O = 2HCO3-) to occur rapidly and also
for the gel layer to swell so that gas permeation is facilitated. Therefore, very
hygroscopic PVA/PAA gel was used as membrane material. The membrane was
prepared by casting an aqueous solution of Cs2CO3 and PVA/PAA copolymer
onto a hydrophilic microporous PTFE membrane followed by heat treatment. In
this membrane, the PTFE membrane pores are filled with the gel and its surface
is covered with the gel, which makes the membrane very stable. The membrane
performance was tested mainly at 160° C by the experiments on the selective
separation of CO2 from a mixture of 5% CO2, 45% H2 and 50% H2O with argon
as sweep gas. The sweep side pressure was usually 20kPa lower than the feed
side pressure. With increasing the feed side pressure, CO2 permeance increased
due to increased water content in the membrane gel layer caused by increased
H2O partial pressure. The highest CO2 permeance, 2x10 -4 mol/(m 2 s kPa), was
obtained at 160C when the Cs2CO3 concentration in the gel layer (dry basis) was
about 70wt%, and the CO2/H2 selectivity was 125. The highest CO2 permeance
and CO2/H2 selectivity were observed at 160C. This may be explained by slower
CO2-carrier reaction rate at lower temperatures and lower water content in the
gel as well as lower chemical equilibrium constant of the reaction at higher
temperatures. However, even at 200C, the observed CO2 permeance was still
high (1x10 -4 mol/(m 2 s kPa)) and the CO2/H2 selectivity was about 80. It was
found that the higher the humidity of the feed gas, the higher both CO2
permeance and CO2/H2 selectivity, which also suggests the importance of water
content in the membrane. Crosslinking of gel layer by glutaraldehyde was found
to be effective to decrease H2 permeation rate by minimizing the defect (pinhole)
formation. The highest CO2/H2 selectivity was as high as 650 with almost the
same CO2 permeance as that observed with the membrane without crosslinking.
This membrane was found to be stable during a long-term experiment for 350 h.
As far as we know, the resent membrane has the highest CO2 permeance and