Hydrogen permeation in palladium-based membranes in the presence of carbon monoxide

A theoretical model is proposed to describe hydrogen permeation in palladium and silver–palladium membranes in presence of a non-inert gas as CO; it is known indeed that hydrogen flux through palladium-based membranes drastically decreases when H2 is fed in mixtures containing carbon monoxide due to the interaction of the latter gas with the membrane surface. To model this process, the adsorption step of the well-known approach suggested by Ward and Dao has been suitably modified, since it must be considered as a competitive adsorption of the different non-inert molecules on the metal interface. In particular, the competitive adsorption of CO and H2 has been examined accounting for the spectrum of information available for CO adsorption on palladium, as well as for hydrogen in palladium and palladium–silver alloys. A validation of the model proposed has been performed through a comparison between several literature data and model calculations, over a rather broad range of operating conditions. A quite good agreement was obtained in the different cases; the model, thus, can be profitably used for predictive purposes.

Research highlights▶ A model to describe H2 flux decrease in Pd-based membranes in presence of CO is considered. ▶ The knowledge of CO adsorption heat is sufficient to estimate membrane behaviour in a broad range of temperature. ▶ At low temperatures CO modifies desorption limited regime into adsoprtion limited regimes on the membrane surface.