Effects of CO and CO2 on hydrogen permeation through a ~3 μm Pd/Ag 23 wt.% membrane employed in a microchannel membrane configuration

摘要

The temperature and concentration dependent effects of CO and CO2 on the performance of a ~3 μm thick Pd/Ag 23 wt% membrane, employed in a microchannel configuration, were investigated. The microchannel system consisted of six parallel channels, 13 mm long, 1 mm wide and 1 mm deep. The membrane permeance was determined to 5.1 × 10~(-3) mol m~(-2) s~(-1) Pa~(-0.5) at 300 °C under pure hydrogen. After the last experiment, a small leakage occurred, that reduced the H2/N2 separation factor to ~3300 at 200 kPa absolute pressure difference.Both CO and CO2 showed an inhibitive effect on hydrogen permeation. The CO effect was strongly dependent on both temperature (275-350 °C) and CO concentration/partial pressure (0-5mol%). The CO inhibition occurred rapidly upon exposure, with a sharp drop in flux between 0 and 0.25 mol% 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 CO2 was slower, and long time exposure was necessary to reach apparently stable values. Only a weak effect was observed at 350 °C, while at 300 °C, a nearly linear decrease was observed over several days. We suggest that the main inhibition mechanism was not CO2 (or CO from reverse WGS) competitive adsorption, but rather a slow formation and removal of strongly adsorbed species.