The Hydrogen Permeability of Sulfur Resistant Palladium-Copper Alloys at Elevated Temperatures and Pressures
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The Hydrogen Permeability of Sulfur Resistant Palladium-Copper Alloys at Elevated Temperatures and Pressures B.H. Howard, A.V. Cugini, R. Killmeyer, K.S. Rothenberger, M.V. Ciocco1, B.D. Morreale1, R.M. Enick2, F. Bustamante3 US Department of Energy, National Energy Technology Laboratory 1 NETL Support Contractor, Parsons 2 NETL ORISE Faculty Fellow, Dept. of Chem. & Pet. Eng., Univ. of Pittsburgh 3 DOE University Partnership Program, Dept. of Chem. & Pet. Eng., Univ. of Pittsburgh ABSTRACT Pd-Cu alloys are being considered for hydrogen membrane applications because of their resistance to sulfur poisoning. Therefore the permeance of Pd-Cu alloys containing 53, 60, and 80 wt% Pd has been determined over the 623 - 1173 K temperature range for H2 partial pressure drops as great as 2.75 MPa. The results indicate that Pd-Cu alloy composition and thermal history influence membrane permeance. The 60%Pd-40%Cu alloy exhibited very high permeance at 623 K, although both the 53%Pd and 60% Pd alloys exhibited a distinct drop in permeability at higher temperatures due to the transition of the Pd-Cu crystal structure from bcc to fcc. Upon cooling the membrane back to 623 K, the permeability of the 60%Pd alloy was initially an order-of-magnitude less than its initial value, but the permeance increased steadily with time as the Pd – Cu crystal structure slowly reverted to bcc. The fcc 80%Pd alloy was less permeable than the bcc 60% Pd alloy at 623 K, but the 80% Pd alloy was more permeable than the fcc 60%Pd alloy at elevated temperatures.
INTRODUCTION The production of hydrogen is expected to increase in the future as the U. S. moves toward widespread use of hydrogen as an energy carrier. Industrial processes, such as coal gasification, produce hydrogen mixed with carbon dioxide and other gases. Advances in the area of membrane technology may improve the efficiency of hydrogen separation and recovery, and thus reduce the cost associated with hydrogen production. A significant technical barrier impeding hydrogen separation membrane development is impurity resistance. Many impurities, most importantly sulfur compounds such as H2S, are part of the gasification product gas mixture. Very dilute concentrations (ppm level) of these sulfur-containing compounds can rapidly deactivate the Pd surface [1-4]. Resistance to sulfur poisoning upon exposure to methyl disulfide has been reported for thin Pd films formed within the macropores of an alumina support [5], and the application of sub-micron films of Pt on Pd has been suggested to enhance sulfur resistance of hydrogen membranes [2, 6-8]. Most investigations of sulfur-resistant hydrogen membranes, however, have focused on the use of Pd alloys. Pd-Cu alloys have exhibited resistance to sulfur poisoning upon exposure to H2-rich retentate streams containing H2S at levels of up to 5 ppm [9], 1000 ppm [10] and (at temperatures greater than 773 K) intermittent exposure to 100,000 ppm [7]. Permeability has also been evaluated with H2S in the hydrogen retentate stream [9, 10] and with s
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