Effects of CO and CO(2) on hydrogen permeation through a 3km Pd/Ag 23wt.% membrane employed in a microchannel membrane configuration

• Published in: Separation and purification technology 2009-08, Vol.68 (2), p.178-184
• Main Authors: Mejdell, A L, Jondahl, M, Peters, T A, Bredesen, R, Venvik, H J
• Format: Article
• Language: English
• ISSN: 1383-5866
• DOI: 10.1016/j.seppur.2009.04.025

The temperature and concentration dependent effects of CO and CO(2) on the performance of a 3km thick Pd/Ag 23wt% membrane, employed in a microchannel configuration, were investigated. The microchannel system consisted of six parallel channels, 13mm long, 1mm wide and 1mm deep. The membrane permeance was determined to 5.1x10(-(3molm(-(2s(-(1Pa(-(0(.(5 at 300(o)C under pure hydrogen. After the last experiment, a small leakage occurred, that reduced the H(2)/N(2) separation factor to ~3300 at 200kPa absolute pressure difference. Both CO and CO(2) showed an inhibitive effect on hydrogen permeation. The CO effect was strongly dependent on both temperature (275-350(o)C) and CO concentration/partial pressure (0-5mol%). The CO inhibition occurred rapidly upon exposure, with a sharp drop in flux between 0 and 0.25mol% CO. The time required to restore the initial flux value after CO exposure became longer when the exposure temperature was lowered. CO desorption hence was the main mechanism for flux restoration at the higher temperatures, while it was controlled by other, slower processes at the lower temperatures. The effect of CO(2) was slower, and long time exposure was necessary to reach apparently stable values. Only a weak effect was observed at 350(o)C, while at 300(o)C, a nearly linear decrease was observed over several days. We suggest that the main inhibition mechanism was not CO(2) (or CO from reverse WGS) competitive adsorption, but rather a slow formation and removal of strongly adsorbed species.