(317x) Hydrogen Sulfide Interactions with Pd and Pd-Cu Alloy Membranes Used for Hydrogen Purification

Coal gasification has been identified as a process with the ability to supply the near- to mid-term hydrogen demand as the United State embarks on the Hydrogen Economy. Unfortunately, the gasifier effluent stream consists of only about 30% hydrogen, with the balance including CO, CO2, and H2O as well as minor constituents such as H2S and NH3. Dense metal membranes have been identified as a promising technology for the separation and purification of hydrogen from the mixed gas effluent stream. Unfortunately, the impurities present in the gasifier effluent streams, such as H2S, can have adverse effects on the mechanical and chemical stability of potential metal membranes in the form of corrosion or catalyst deactivation, respectively.

Therefore, a major obstacle of current membrane research is the identification and characterization of potential metals that tolerate the harsh environments encountered in the gasification process without significant detrimental effects on performance. Pd-Cu alloys have been of interest in recent years due to its catalytic activity for hydrogen, high permeability with respect to Pd content, suppression of the hydride-phase transition and reported stability in the presence of H2S.

In this study, the interaction of H2S with Pd and select Pd-Cu alloys is being evaluated with the goal of correlating changes in membrane performance with temperature, alloy structure and corrosion behavior. Experiments determining the influence on hydrogen flux and well as sulfide growth rates on pure Pd and the 80, 60 and 53wt% Pd-Cu alloys were observed in the presence of 1000 ppm H2S in H2 at 350, 450 and 635oC. Following membrane testing and corrosion exposure, the samples were characterized by SEM/EDS and XRD to determine morphological, chemical and crystalline changes observed within the sample surface. Results indicate that the temperature, composition and possibly crystalline phase plays a significant role in the observed experimental results. In this study, the observed degradation of hydrogen flux of pure palladium membranes appears to be governed by the formation of a rapid growing sulfide scale, while the effect of H2S on the PdCu system is much more complicated.