A multi-layer model for double-skin Pd-based membranes: Layer-by-layer parameter fitting

The Pd-based double-skin (DS) membrane has high potential to be implemented in various industrial processes. However, its multi-layer structure makes it difficult to model and understand the limiting transport mechanisms through each of these layers. In this work an extensive set of experiments on several membranes with different configurations was performed with the purpose of deriving a detailed model for the double-skin Pd-based membrane. This is important for the general understanding of the mass-transport taking place within each of the membrane layers, namely the support, the selective and the protective layer. Characterization, permeation tests and data-fitting led to the construction and validation of a multi-layer model for the DS-membrane. The experimental results also pointed out that the protective layer of HT or YSZ/Al₂O₃ has only a minor or negligible effect on the overall transport resistance of the membrane. The influence of the support was found to be small but not negligible compared to the dominating resistance of the dense selective PdAg layer. Experiments and simulations of the membrane permeation in multi-component mixtures also highlighted the large importance of concentration polarization and H₂ depletion, which were successfully described in the model using a film-layer model together with a Sherwood correlation.