(574c) Controlling Sulfur Corrosion of Pd-Cu Hydrogen Separation Membranes with Ultra-Thin Metal Films | AIChE

(574c) Controlling Sulfur Corrosion of Pd-Cu Hydrogen Separation Membranes with Ultra-Thin Metal Films


O'Brien, C. - Presenter, University of Notre Dame
Palladium-copper (Pd-Cu) alloy hydrogen separation membranes are promising alternatives to pure Pd membranes due to their higher permeability to hydrogen and their improved resistance to bulk corrosion from H2S—a common contaminant in hydrogen-containing gas streams—relative to pure Pd. However, the catalytic surface of Pd-Cu alloys is poisoned by ppm concentrations of H2S, which severely inhibits hydrogen transport across the membrane. In this talk, I will discuss our efforts to engineer sulfur-tolerant catalytic coatings for Pd-Cu alloy membranes. Thin metal (Pd, Mo, Ni, Co, Cr) films with thicknesses ranging from ~monolayer up to 1000 nm thickness were deposited onto Pd-Cu substrates. The composite metal/Pd-Cu membranes were then exposed to 1000 ppm H2S/10% He/balance H2 in a membrane permeation apparatus to evaluate the sulfur tolerance of hydrogen transport across the composite membranes. The interactions of H2S with the composite membranes were characterized by compositional analysis of the membranes before and after permeation testing. The thickest Pd film (1000 nm) was converted to a Pd4S-like compound, which significantly increased rates of hydrogen transport across the membrane relative to the unmodified Pd-Cu membrane during H2S exposure. However, the reaction of the Pd film with H2S was more complex than expected, and the H2 flux across the composite membrane was lower than predicted. The metal element and the film thickness had a strong influence on both the interaction of the composite membranes with H2S and the hydrogen permeation behavior of the membrane. Monolayer-thick films of all of the metals compromised the corrosion resistance of the Pd-Cu substrate and catalyzed the bulk reaction of Pd-Cu with H2S to form two different metal-sulfide corrosion products—Cu2S and Pd13Cu3S7. These results demonstrate that (1) Pd4S is a promising sulfur-tolerant coating material, and (2) the Pd-Cu substrate is not thermodynamically corrosion resistant; sulfidation of the Pd-Cu substrate is kinetically limited by a surface reaction that is catalyzed by the thin metal films.