(397c) Effect of Temperature, Air Exposure and Gas Mixture on Pd82-Ag15-Y3 Membrane for Hydrogen Separation

Energy consumption is significantly increasing due to population and economic growth worldwide. As a result, more CO₂ is emitted into the environment by burning fossil fuels to provide energy. Hydrogen is considered as the clean energy carrier of the future since it produces only water when fed to a Proton-Exchange Membrane Fuel Cells (PEMFCs). Currently, H₂ is mainly produced by the methane steam reforming, which is an energy-intensive process emitting approximately 9 kg_CO2/kg_H2-produced. Membrane reactors (MRs) provide a great opportunity for carbon-neutral hydrogen production where hydrogen is produced and simultaneously separated by a membrane, while CO₂ is collected in the downstream of the MR system, which can be later captured. The MR offers several benefits, such as enhances the yield of reactions and products selectivity. Pd-based MRs are mainly studied for their characteristics of being completely selective towards H₂ permeation. Nevertheless, pure Pd membranes suffer from drawbacks such as embrittlement effect, low thermal and chemical resistance. It has been found that the addition of some metals, such as Ag, Cu, Au, and Y, to the Pd membranes can improve their performances. Ternary alloys can be considered to improve the membrane properties in terms of H₂ permeation, mechanical and resistance to poisonous materials. For instance, the addition of Ag and Y to pure Pd membranes has shown enhancement in permeability, stability and resistivity [1–3]. However, more studies need to be performed to understand the effect of gas mixtures on Pd alloy membranes. [4,5].

In this work, material characterization, hydrogen permeation and separation properties of a ternary Pd₈₂-Ag₁₅-Y₃ are evaluated by feeding several gases and mixtures at temperature of 300 – 600 °C and pressure ranges of 1.0–3.0 bar (abs). The Pd₈₂-Ag₁₅-Y₃ membrane was unsupported, prepared by cold rolling and was characterized by ~ 38 μm of thickness. The membrane showed good thermal and chemical stability when exposed to air and at different temperature. However, several agglomerates on the surface, consisting in metal oxides, are formed at the highest temperature, such as 600 °C. At 400 °C and at various pressure, the membrane showed an H₂ permeability of 7.910^-11 mol.m^-1.s^-1.Pa^-0.9 and an “n” value of 0.9 due to the presence of Y. These values are in agreement with the literature. The effect of other gases, such as N₂, CH₄, CO₂ and CO on the H₂ permeating flux are also evaluated. The data show that CO has the highest negative effect on the H₂ permeating flux. The order of inhibition effect on H₂ permeation for the gases is CO> CO₂> CH₄> N₂. Finally, the SEM, EDS, AFM and XRD analysis are performed to observe any changes in the surface and structure of pristine and used membrane.

References

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