287880 Long Term Thermal Stability of Pd and Pd-Alloy Composite Membranes
Long Term Thermal Stability of Pd and Pd-alloy Composite Membranes
Hani Abuelhawa1, Oyvind Hatlevik1, Stephen N. Paglieri2, Aadesh Harale3, and J. Douglas Way1
1Department of Chemical & Biological Engineering, Colorado School of Mines,
Golden, CO 80401, USA
2TDA Research Inc., Wheat Ridge, CO 80033, USA
3 Saudi Arabian Oil Company, Dhahran, 31311, KSA
The integration of a Pd-based membrane within a catalytic reforming reactor to produce hydrogen has received much more attention during the last few decades . In addition to being permselective to hydrogen, Pd-based membranes are capable of maximizing the conversion of thermodynamically-limited reactions, such as the steam reforming of methane, beyond the equilibrium conversion based on the feed composition, by simply withdrawing the hydrogen from the reaction mixture as it forms. However, there are still some issues that prevent this technology from being fully commercialized, such as the long term thermal stability and the chemical tolerance of these membranes in real-world mixed gas environments.
Guazzone, et al.  has investigated the long term thermal stability of electrolessly plated pure Pd membranes by identifying the mechanism that leads to the leak evolution in hydrogen atmosphere. They concluded the leak evolution is a thermally-activated process induced by the self-diffusion of Pd at temperatures above 400°C. In this work, we will investigate the thermal stability of Pd and Pd-alloy membranes such as PdRu, PdAu, and/or PdAg. Previous literature  has investigated the performance and properties of Pd-alloy membranes, however, the long term thermal stability of these alloys did not receive so much attention.
In this paper, long term high temperature stability data for a 5.1 micron thick sequentially plated PdAu10wt% membrane prepared by the electroless plating method on a porous-zirconia/porous-stainless-steel support will be discussed. The membrane has been tested for approximately 1000 hours and showed superior thermal stability at 500°C and below, in comparison to similar pure Pd membranes. The membrane also maintained an ideal H2/N2 pure gas flux ratio of at least 1000 at 100 psig for more than 1000 hours of testing. As shown in Figure 1, nitrogen leak did not grow significantly in the temperature range (450-500°C) during several hundred hours of testing. Figure 2 compares the performance of PdAu membrane to a pure Pd of similar thickness at 500°C. Addition of Au to Pd enhanced the thermal stability of the membrane by reducing the leak rate by at least one order of magnitude. Additionally, by comparing the leak rate of this PdAu membrane with the results of Guazzone, et al.  for a pure Pd membrane of comparable thickness, the leak growth rate in the PdAu membrane is also lower by at least one order of magnitude. The calculation of the activation energy of the leak growth rate in Pd-alloy membranes and comparing it to the Pd self-diffusion activation energy could give some insights in revealing the leak growth mechanism in these membranes.
 Ř. Hatlevik et al., Separation and Puriﬁcation Technology 73 (2010) 59–64
 F. Guazzone et al., AIChE Journal, (2008) Vol. 54, No. 2, 487-494.
Figure (1): The high temperature thermal stability data for the 5.1 micron PdAu10wt% membrane deposited on zirconia/SS porous support.
Figure (2): A comparison of the thermal stability data of a PdAu10wt% and a pure Pd control at 500 °C, 100 psig. Both Membranes are of comparable thickness.