Effect of Co-existing gases on hydrogen permeation through a Pd82-Ag18/α-Al₂O₃ membrane during transient start-up

The work aimed to study the influence of co-existing gaseous mixture (H₂-N₂-CO-CO₂) on hydrogen permeation through the counter-current flow of a Pd82-Ag18/α-Al₂O₃ membrane during transient start-up at 350 °C and atmospheric pressure. The membrane was operated for an 8-h. Its performance was measured in terms of hydrogen flux and recovery. The results were mapped on Sieverts-Fick's line and showed a slight membrane deactivation because of the presence of N₂ and CO₂ in the feed gas. The membrane deactivation became more profound when CO was a constituent. The effect of the co-existing gases on the hydrogen flux, in increasing order, was CO > CO₂>N₂. The co-existing gases, if present as a significant fraction, induces dilution, concentration polarization, and inhibition over the membrane surface, decreases the membrane performance in term of hydrogen recovery, time lag during transient start-up, and deactivation. It is recommended that the start-up might be run using equimolar H₂-N₂ mixture.