Concentration Polarization in Palladium-Based Membrane Tube with High Permeance

Concentration polarization, a retarding effect upon hydrogen permeation across a membrane, will affect the performance of hydrogen separation and purification. 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 in the present study. Three important parameters, consisting of H2 partial pressure difference, flow rate at the exit of the retentate side and H2 concentration in 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, and decreasing the concentration of H2 in the feed gas tends to deteriorate the polarization. The sensitivity of polarization to H2 concentration is higher when the concentration of H2 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.