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SULFUR POISONING AND TOLERANCE OF HIGH PERMEANCE Pd/Cu ALLOY MEMBRANES FOR HYDROGEN SEPARATION

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<p>This work investigated the long-term stability of sulfur tolerant Pd/Cu alloy membranes for hydrogen separation by performing characterizations lasting several thousand hours in H<SUB>2</SUB>, He and H<SUB>2</SUB>S/H<SUB>2</SUB> atmospheres ranging in concentration from 0.2 – 50 ppm and temperatures ranging from 250 - 500ºC. Two methods were used for fabricating the Pd/Cu membranes so that the sulfur tolerant fcc alloy would remain on the surface and minimize the decrease in hydrogen permeance inherent with fcc Pd/Cu alloys. The first method consisted of annealing a Pd/Cu bi-layer at high-temperatures and the second consisted of depositing a Pd/Cu/Pd tri-layer with an ultra-thin surface alloy. High temperature X-ray diffraction (HT-XRD) was employed to study the kinetics of the annealing process and atomic adsorption spectroscopy (AAS) was used to investigate the kinetics of the Cu deposition and Pd displacement of Cu.</P> <P>Upon the introduction of H<SUB>2</SUB>S, the permeance decrease observed was dependent upon the H<SUB>2</SUB>S feed concentration, and not the time of poisoning. However, after the recovery in pure H<SUB>2</SUB> there was a portion of the permeance which could not be recovered due to adsorbed sulfur blocking H<SUB>2</SUB> adsorption sites. The amount of recoverable permeance was dependent on the time of exposure to H<SUB>2</SUB>S and reached a limiting value which decreased with temperature. X-ray photoemission spectroscopy (XPS) was used to investigate poisoned samples and it was observed that the permeance not recovered at a given temperature in H<SUB>2</SUB> was caused mostly by Cu sulfides.</P> <P>Both bi-layer and tri-layer membranes had hydrogen permeances which were higher than homogeneous Pd/Cu membranes of the same surface concentration. However, the tri-layer membranes performed as well as Pd membranes thus eliminating the disadvantage of alloying Pd with Cu without sacrificing sulfur tolerance.</P>

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  • English
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  • etd-082710-112402
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  • 2010
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  • 2010-08-27
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