An integrated two stages inorganic membrane-based system to generate and recover decarbonized H2: an experimental study and performance indexes analysis

This work focuses on the utilization of a two stages inorganic membrane-based system to generate and recover decarbonized hydrogen in order to meet the targets set by the European Clean Hydrogen Partnership under the Strategic Research & Innovation Agenda 2021-2027. In the first stage, a CH4:CO2 = 60:40 mixture simulating a biogas stream is used to generate a COx-free hydrogen via steam reforming reaction carried out in a tubular Pd- Ag membrane reformer, packed with a novel non-commercial 7 wt%Ni-0.5 wt%Ru/La0.3Y0.3Zr0.4Ox catalyst, prepared by solution combustion method. The catalyst was characterized by XRD, TPR and TEM techniques. The analyses reveal well-distributed active metal particles interacting differently with the support (weakly and strongly). In particular, the XRD pattern shows the formation of perovskite and nickel oxide in addition to the pyrochlore phase. This behaviour indicates a low solubility of Ni in the pyrochlore structure. Reaction measurements were carried out at a temperature of 673 K, in the total pressure range between 250 kPa ÷ 350 kPa, weight hourly space velocity (WHSV) of 0.2 h? 1, H2O/CH4 feed molar ratio between 1.5 and 2, feeding N2-sweep gas in the permeated side. As best results of Stage 1, CH4 conversion equal to 99% (@ H2O/CH4 feed molar ratio = 2 and feed pressure of 250 kPa) and a COx-free H2 recovery of 40% were reached. In the second stage, the unpermeated stream of Stage 1 rich in hydrogen was fed to a supported Pd/Al2O3 membrane separator to further recover high grade hydrogen at the same temperature and total pressure set in Stage 1. The maximum hydrogen recovery equal to 67% was reached at 673 K and 350 kPa, with a purity of the recovered stream equal to 99.9%. The total hydrogen recovered in the permeate streams of Stage 1 and Stage 2 was equal to 80% of the total hydrogen produced during the steam reforming reaction, showing an average purity equal to 99.99%, which allowed to meet the established targets. The work further analized and discussed the experimental results of the integrated system by means of performance indexes.