Model development and validation of hydrogen transport through supported palladium membranes

Porous matrices are often used to provide structural support to thin Pd-based metallic membranes in H2 separation applications. Optimizing such composite membranes requires detailed understanding of all possible rate-controlling processes including surface and bulk processes in the metal and diffusion of gases through the porous media. In the work described in this paper, we fabricate a composite membrane by depositing a thin (∼5-6 μm) Pd film on a porous α-Al2O3 tube and then measure the H2 permeance of this composite membrane over a range of operating conditions. The rate-controlling processes for the H2 permeation are evaluated with a computational model which combines a detailed thermo-kinetic Pd-H2 interaction model and a porous media transport model. The Pd-H2 thermo-kinetic model is validated against literature data, and the porous media transport model is independently calibrated using experimental measurements. The combined composite membrane model gives good agreement with experiments over a large range of temperatures (250-450 °C) and H2 partial pressures (100-385 kPa). This validated model is then used to analyze the importance of design parameters such as Pd thickness and support micro-structure on H2 flux through the membrane. These parametric studies will also aid in assessing trade-offs between membrane structural robustness and overall performance.