Preliminary analysis of mass dispersion in solid foams. Separation of nitrogen/hydrogen mixtures in a packed membrane module as a case study

Membrane reactors for low-temperature hydrogen production are receiving significant attention. The main design challenges include the choice of appropriate membranes, catalysts, and catalyst supports. Research on the mechanical supports has been addressed towards the use of solid foams; however, information regarding mass dispersion within these foams is still lacking, even though the resistance to mass transport in the packed bed may become relevant when using a good catalyst and a high-permeability membrane. The aim of the present work is to carry out a preliminary analysis of mass dispersion in solid foams. To this end, experiments have been carried out for hydrogen separation from binary hydrogen/nitrogen mixtures using a packed membrane separator. The configuration adopted consists in two co-axial cylinders. A Pd-based membrane, permeable to hydrogen only, is placed on the outer wall of the innermost tube. A SiC solid foam is placed in the volume between the two cylinders. Experimental results were analyzed with the support of a 2D isothermal model of a packed membrane separation module, previously developed by some of the same authors of this study. The model has been used to fit an effective Péclet number (Peeff) in each condition. These values were then compared to the molecular Péclet number (Pe). The solid foams were found to convey lower dispersion than traditional packed beds and the lower axial dispersion favors the overall separation efficiency.