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The permeances of two palladium (Pd) membranes in pure H2, binary and ternary gas mixtures are investigated experimentally. With 10% of gas impurities (N2, CO2, or CO) in H2, the profiles of dimensionless permeance suggest that H2 permeation rate is lessened by approximately 50% to 90%, and the permeance reduced by the gas impurities is ranked as CO > CO2 > N2. By introducing a parameter of permeance resistance, which is the reciprocal of permeance, the permeance resistance in a ternary gas mixture can be predicted from the summation of individual permeance resistances in binary gas mixtures, revealing no synergistic effect exhibited from the interaction of contaminants. At least 75% and up to 100% of H2 in the gas mixtures can be recovered in the membrane system, and the maximum H2 recovery develops at the H2 partial pressure difference of 2 or 3 atm. In the Arrhenius-type equation describing the relationship between the permeance and temperature, the activation energy is between approximately 2 and 18 kJ mole−1. In general, the permeances of the membranes in gas mixtures, especially in ternary gas mixtures, are more sensitive to temperature when compared with those in pure H2, stemming from lower activation energy exhibited. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hydrogen purification using palladium (Pd) membrane technology has been seen as a potential solution for producing pure hydrogen form hydrogen-rich gas. Compared to traditional practices of operating the permeate side of the membrane at atmospheric pressure, in this study, a vacuum is applied. The effects of various vacuum degrees applied to the permeate side of the Pd membrane are investigated and compared to the results under normal operation without a vacuum. The feed gas used for experiments consists of a mixture of hydrogen (70 vol%) and nitrogen (30 vol%). Three membrane operating temperatures (320, 350, and 380 °C), four pressure differences (2, 3, 4, and 5 atm) across the membrane, and four vacuum degrees (−15, −30, −45, and −53 kPa) applied to the permeate side are considered. For the three operating temperatures, the best improvements in the performance of hydrogen permeation are at 320 and 350 °C when a −53 kPa vacuum is applied, resulting in 79.4% and 79.1% improvements, respectively, compared to normal operations. Increasing temperatures leads to an increase in H 2 permeation both with and without a vacuum; however, best performances of H 2 permeation are observed in cases without a vacuum. Image 1 • A vacuum pressure greatly influences H 2 permeation compared to normal operating conditions. • A lower vacuum has a more significant effect on the improvement of H 2 permeation. • Vacuum conditions posed improves H 2 permeation up to 79% at 320 °C and 350 °C. • Increasing the H 2 partial pressure difference deteriorates the concentration polarization. • Vacuums aid in diminishing the concentration polarization on the membrane surface. [ABSTRACT FROM AUTHOR]

Highlights: [•] Concentration polarization phenomena in membrane tubes are studied. [•] Two pure palladium (Pd) membranes and one Pd–Cu alloy membrane are tested. [•] Concentration polarization is clearly exhibited when the gas mixture is fed. [•] Decreasing H2 concentration in the feed gas deteriorates polarization. [•] For tested gas mixtures, the permeance is reduced by 1–2 orders of magnitude. [ABSTRACT FROM AUTHOR]

Palladium (Pd) membranes are characterized by their high permselectivity to hydrogen and easy operation, and are promising devises for separating hydrogen from hydrogen-rich gases. The membranes are normally operated with atmospheric pressure at the permeate side. Instead of this common operation, hydrogen permeation through a Pd membrane under vacuum operation at the permeate side is investigated and compared with that under normal operation. In this study, two membrane operating temperatures (320 and 380 °C), four H 2 partial pressure differences (2, 3, 4, and 5 atm) across the membrane, and four feed gases are considered. The results suggest that the vacuum operation can efficiently intensify the H 2 permeation rate. The improvement in H 2 permeation rate due to the vacuum operation can be increased up to 136%. The positive effect of the vacuum operation is especially pronounced when the gas mixtures are used as the feed gases, stemming from the effective attenuation of the concentration polarization. An increase in membrane temperature raises the H 2 permeation rate, but its influence in enhancing the H 2 permeation rate with the vacuum operation is not as significant as that without the vacuum one. It is found that the retardation effect of impurities on the mass transfer is always ranked as CO > CO 2 > N 2 , regardless of with/without vacuum operation. • Hydrogen separation by a palladium (Pd) membrane with/without vacuum is studied. • Vacuum operation can intensify the H 2 permeation rate significantly, especially in gas mixture. • Vacuum operation can effectively attenuate H 2 boundary layer and concentration polarization. • Retardation effect of impurities on H 2 permeation rate follows the order of CO > CO 2 > N 2. • Improvement in H 2 permeation rate by vacuum operation can be intensified up to 136%. [ABSTRACT FROM AUTHOR]

Abstract: 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 H2 in membrane tubes, H2 permeation and recovery characteristics of two high-permeance Pd membranes are investigated. Four important factors influencing H2 permeation, namely, the H2 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 H2–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. [Copyright &y& Elsevier]