Hydrogen transport in Pd-based supported membranes was described by means of a model considering several elementary steps of the permeation process, improving that of Ward and Dao (1999) for self-supported membranes. The model included the external mass transfer in the multicomponent gaseous phases on both sides of the membrane, described by the Stefan–Maxwell equations. The transport of the multicomponent mixture in the multilayered porous support was also considered and described by means of the dusty gas model, which takes into account Knudsen, Poiseuille and ordinary diffusion. The diffusion in the Pd-alloy layer was modelled by the irreversible thermodynamics theory, taking the hydrogen chemical potential as the driving force of the diffusion in the metallic bulk. The interfacial phenomena (adsorption, desorption, transition from Pd-based surface to Pd-based bulk and vice-versa) were described by the same expressions used by Ward and Dao (1999). Thicknesses of 1 and 10μm were considered for the Pd-alloy layer. The asymmetric support consisted of five layers, each one characterized by a specific thickness and mean pore diameter. The model separates the permeation steps and consequently their influence, quantifying the relative resistances offered by each of them. Comparison with some experimental data in several conditions in the literature exhibited a good agreement. The developed tool was able to describe hydrogen transport through a supported Pd-based membrane, recognizing the rate-determining steps (e.g., diffusion in the metallic bulk or in the porous support) involved in the permeation.

Modelling and Simulation of Hydrogen Permeation Through Supported Pd-Alloy Membranes with a Multicomponent Approach. A.Caravella, G.Barbieri, E.Drioli: Chemical Engineering Science, 2008, 63[8], 2149-60