Polarization phenomena of hydrogen-rich gas in high-permeance Pd and Pd–Cu membrane tubes

Concentration polarization, a retarding effect upon hydrogen permeation across a membrane, will affect the performance of hydrogen separation. To recognize the concentration polarization behavior of hydrogen-rich gas in high-permeance membrane tubes, three palladium-based membranes with two pure palladium (Pd) membranes and one Pd–Cu alloy membrane are tested. Three important parameters, consisting of the H2 partial pressure difference, the flow rate at the exit of the retentate side and the H2 concentration in the feed gas mixture (H2+N2), are taken into account. A comparison to pure H2 permeation suggests that the concentration polarization is clearly exhibited when the gas mixture is fed. Decreasing the H2 concentration in the feed gas tends to deteriorate the polarization phenomenon. The sensitivity of polarization to H2 concentration is higher when its concentration in the feed gas is larger. For the gas mixtures with 50 and 75 vol% of H2, the permeances of the membranes are reduced by 1–2 orders of magnitude. The permeances of the membranes are also affected a bit when the H2 partial pressure difference or the flow rate is altered.