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 75vol% 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.