(362e) Long-Term Hydrogen Characterization of Composite Pd and Pd-Ag Membranes Synthesized from Agitated Electroless Pd and Ag Plating Baths

Hydrogen separation technologies are of great importance due to the essential nature of H₂ as an alternate clean energy carrier and the increasing demand for hydrogen in various chemical and petrochemical industries. Composite Pd and Pd/alloy membranes prepared by the electroless plating on porous sintered metal supports are well-suited for high purity H2 production in steam reforming reactors, as well as in H₂ separation and purification. Membrane synthesis via electroless plating is a widely used technique to form uniform deposition on surfaces with complex geometries and large surface areas and with the added advantages such as the hardness of the deposited film, good adhesion to the substrate, and simple equipment and ease of scale-up. Although there are only few studies in the literature that discuss the effects of plating parameters on the deposition rates from hydrazine-based plating baths, the effect of external mass transfer on the electroless plating rates of Pd and Ag has not been quantified yet. The objective of this study was twofold: To investigate the effects of bath agitation to elucidate the effect of external mass transfer on the electroless plating rates and the deposition morphology of Pd and Ag metals and to study the long-term H₂ permeation characteristics of composite Pd and Pd/Ag membranes synthesized from agitated electroless Pd and Ag plating baths. For this purpose, atomic absorption (AA) flame analysis was successfully utilized for the measurement of the Pd and Ag ion concentrations in the plating baths. It was found that the electroless plating of both Pd and Ag were strongly affected by the external mass transfer in the absence of bath agitation. The external mass transfer limitations for both Pd and Ag deposition have been minimized at or above an agitation rate of 400 rpm, resulting in a maximum conversion of the plating reaction at 60°C and dramatically shortened plating times with an added advantage of uniform deposition morphology as evidenced by the SEI micrographs. Furthermore, a 5 µm thick pure-Pd and a 20 µm thick Pd/Ag (10 wt% Ag) membrane, designated as 025 and 022, respectively, were prepared on media-grade 0.1 µm, ½? OD and 2? long porous Inconel tubes, which were oxidized at 800°C for 12 hours in order to form an intermetallic diffusion barrier. The H₂ permeance for the membranes 022 and 025 at 400°C was 22 and as high as 63 m³/m²-h-atm^0.5, respectively. In addition, after a total testing period of 870 and 690 hours in the temperature range of 300-500°C, the H₂/He selectivity for the membranes 022 and 025 were ~200 and over 310, respectively.