(268f) Hydrogen Purification with Palladium Alloy Membranes

As the economy migrates from fossil fuels to hydrogen membrane purification of H₂ is becoming increasingly important. Critical to this H₂ purification is the rejection of impurities such as CO and SO₂ to produce ultra high purity grade (>99.999%) H₂. Pd and Pd alloy membranes are especially suited for both low and high temperature hydrogen separation applications. Alloying Pd particularly with Ag not only suppresses hydrogen embrittlement, but also increases the permeability of the alloy membrane. The main objective of this work was to develop a membrane via a simultaneous electroless plating of Pd and Ag onto a 0.5 µm media grade porous stainless steel to act as a H₂ purifier. Effects of the electroless bath temperature, composition, annealing time, and temperature were studied while developing the Pd coating. The topography and the homogeneity of the developed membrane were analyzed via SEM-EDS and AFM. Very low N₂ fluxes were seen, ranging from 0.010 - 0.020 cm³/cm²-min at temperatures varying from 300^oC - 400^oC. Although the exact source of this modest leak could not be pinpointed, the presence of pinholes or grain boundary diffusion could not be ruled out. Stable H₂ permeances from (1.9?3.1) × 10^-2 cm³/cm²-min-Pa^0.5 were recorded between 350^oC - 550^oC. Sievert's Law was seen to hold true at all temperatures with regression coefficients between 0.95 ? 0.99.