Hydrogen permeation and recovery from H₂-N₂ gas mixtures by Pd membranes with high permeance

Hydrogen separation from H₂-N₂ gas mixtures by means of high-permeance Pd membranes is an appropriate route to gain pure hydrogen for fuel cell applications. To figure out the mass transfer phenomena of H ₂ in membrane tubes, H₂ permeation and recovery characteristics of two high-permeance Pd membranes are investigated. Four important factors influencing H₂ permeation, namely, the H ₂ pressure difference, H₂ concentration, the flow rate at the exit of the retentate side, and membrane temperature, are taken into account. The experimental results suggest that decreasing H₂ concentration, flow rate, and temperature reduce the permeances of the membranes and H₂ recovery, even though the H₂ pressure difference is identical. The dimensionless permeance, a permeance ratio between H ₂-N₂ gas mixture and pure H₂ as feed gases, is used to evaluate the extent of concentration polarization. Within the investigated ranges of the four factors, the dimensionless permeances of the two membranes are in the ranges of 0.022-0.206 and 0.042-0.359, respectively, revealing that the concentration polarization diminishes the permeance of the membranes down to the level within two orders of magnitude. Nevertheless, over 46% of H₂ is recovered.