FREQUENCY-DOMAIN ANALYSIS OF HYDROGEN PERMEATION ACROSS PALLADIUM METALLIC MEMBRANES

Hydrogen permeation (ie. hydrogen transport across metallic membranes), is an industrial process used for purification purposes. Palladium alloys are generally used as permeation materials, at operating temperatures above the critical value, to avoid the precipitation of hydride phases. In state of the art systems, a few tens of microns thick metallic membranes are used and rate limitations come from bulk atomic H diffusion. Because of cost considerations, it is necessary to reduce the thickness of these membranes. In the micron-thick range, surface contributions are expected to become rate determining, especially when the membrane is positioned on the exit side of a gas reformer used for the production of pure hydrogen from natural gas or bio-fuels. For such applications, corrosion problems are expected to appear on the upstream side of the membrane, yielding additional surface resistances. There is therefore a need to separately measure surface and bulk rate contributions during permeation processes. In this communication, a new experimental equipment and a new treatment procedure are proposed to analyze the dynamics of hydrogen permeation across metallic membranes. Permeation can be conveniently analyzed in the frequency domain, yielding information on the different steps involved in the overall mechanism. Raw kinetic data such as transient pressur