288091 Hydrogen Permeation Through Pd Membranes with/without Deposited Cu Catalyst

Tuesday, October 30, 2012: 2:10 PM
402 (Convention Center )
Abdulrahman Y. Alraeesi, Chemical Engineering, UAE University, Al Ain, United Arab Emirates and Tracy Q. Gardner, Colorado School of Mines, Golden, CO

Hydrogen permeation through Pd membranes with deposited Cu catalyst.

This study presents the fundamental aspects of hydrogen transport through palladium membranes, with and without deposited catalyst films. Understanding the transport through such systems is important for properly analyzing and predicting the performance of membranes and associated catalysts in catalytic membrane reactors. Hydrogen permeation was investigated through palladium-based membranes under conditions that would be used in applying them as catalytic membrane reactors. The potential for using palladium-based membranes with deposited catalyst films as catalytic membrane reactors is to improve reaction yield and selectivity for hydrogenation reactions. Copper catalysts were uniformly deposited on Pd membranes with different geometries and thicknesses via electrodeposition using a novel masking technique developed in this work. Deposition was as continuous films or as islands on one side of the foils (permeates side). These films (or islands) were annealed to cupric oxide that reduced to Cu, which subsequently diffused into the membrane during long-time H2 permeation studies (see Figure 1).

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Figure 1.  SEM image of as-deposited Pd1CC60 foil

 Short-time and long-time transient studies after exposing the membranes to various gas atmospheres and temperatures elucidated the effects of the membrane “history” on performance. The transient studies indicated that the membrane structure changes during permeation (see Figure 2), resulting in faster hydrogen permeation.

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Figure 2 SEM image of Pd1CC60 foil after annealing followed by hydrogen permeation studies

Fluxes through the uncoated Pd-3 were the highest, ranging from ~8 to 15 mmol/m2.s. At the other extreme, fluxes of ~0.5 to 1 mmol/m2.s were measured for the Pd1CC60; the thickest continuous film studied. The two Pd/Cu foils with islands (Pd1IsV60 and Pd1IsC7) had nearly identical fluxes (see Figure 3) even though the deposition times were 60 and 7 seconds, respectively. Compare fluxes through the foils with continuous films, it is clear that the flux decreases with Cu film thickness. Finally, fluxes through all of these membranes followed Sieverts' law.

It was concluded from this and other results that diffusivity in the membrane material likely increases with hydrogen coverage for the conditions studied.

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Figure 3 Long-time H2 fluxes through uncoated Pd-3 and Pd/Cu foils at 473 K and feed pressures of 124, 138, 152, and 165 kPa with permeate at 93 kPa


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