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Pd-based membranes offer energy efficiency and economic advantages, providing a promising route for hydrogen separation and recovery from several streams. Alloying Pd with other elements increases its resistance to corrosive gases while improving H 2 permeability. This study investigated the permselective properties of PdNiAu membranes with different Ni contents (17, 23, and 27 at.% Ni) in pure H 2 and under CO/He/H 2 and H 2 S/H 2 mixtures. The permselective properties were evaluated at different temperatures (573–723 K) and pressure differences across the membrane (ΔP: 10–100 kPa). The membranes studied exhibited promising H 2 permeation properties; the highest permeability at 673 K and 100 kPa was obtained with the membrane containing 23 at.% Ni (2.1 × 10−8 mol m−1 s−1 Pa−0.5). All membranes exhibited high H 2 /N 2 selectivity (>10,000). Regarding chemical stability, the membranes with 23 and 27 at.% Ni, showed high tolerance to inhibition by CO and H 2 S. These results suggest that increasing Ni improves membrane performance in streams containing CO or S; however, the high chemical resistance of the membranes could be attributed to both Ni and Au. [Display omitted] • PdNiAu membranes showed potential for H 2 purification from pollutant streams. • The highest permeability (2.1 × 10−8 mol m−1 s−1 Pa−0.5) was obtained at 23 at.% Ni. • Membranes with high Ni content showed high resistance to inhibition by CO. • The H 2 S exposure did not significantly affect the performance of the PdNiAu membranes. [ABSTRACT FROM AUTHOR]

Abstract: Pd, Pd90Ag10, Pd91Au9, Pd78Ag9Au13 and Pd75Ag16Au9 alloy membranes were prepared on vacuum-assisted ZrO2-modified porous stainless steel supports by sequential electroless deposition. The membranes were evaluated for permeability in pure H2 and in an H2S/H2 mixture. The membranes displayed a range of permeabilities in pure H2: Pd90Ag10>Pd78Ag9Au13>Pd~Pd75Ag16Au9>Pd91Au9. On exposure to 100ppm H2S/H2 at 673K for 24h, all membranes lost a significant fraction of their H2 permeabilities: Pd (lost the largest fraction, 85%)>Pd90Ag10>Pd75Ag16Au9>Pd78Ag9Au13>Pd91Au9 (60%). When H2S was removed, the membranes recovered the lost permeability to different extents. The Pd91Au9 and Pd78Ag9Au13 membranes displayed the highest fractional recovery of initial H2 permeability (~80%). But, with its higher initial pure H2 permeability, Pd78Ag9Au13 had the highest absolute H2 permeability after recovery. The microstructure, morphology and bulk composition of H2S-exposed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). XRD revealed the presence of a bulk Pd4S phase on both Pd and Pd90Ag10, the membranes that recovered the least H2 relative flux after their exposure to H2S. In contrast, bulk sulfides did not form on Pd91Au9 or on PdAgAu ternary alloys. In agreement with the XRD results, EDS did not detect sulfur in the bulk of Pd91Au9 or in either of the ternary alloy samples. Our results show that the addition of Au to the high-permeability PdAg binary membrane results in a PdAgAu ternary membrane that minimizes the permanent H2 flux loss associated with H2S exposure by preventing the formation of thick stable sulfides. [Copyright &y& Elsevier]

Abstract: A ZSM-5 membrane synthesized on a stainless steel porous tube was used for the separation of p-xylene from its isomers, m- and o-xylene. The membrane was prepared by secondary growth on the outer surface of the support. The permeation regime through the membrane was described by a combination of adsorption–diffusion steps. In order to examine the durability of the membrane, a sequence of three thermal cycles was conducted. N2 permeation measurements together with scanning electron microscopy (SEM) observations were the tools used to detect whether or not cracks developed after exposure to the xylene isomers up to 400°C. After 1000h on stream, the membrane was selective to p-xylene, the N2 permeance fluxes remained unchanged and the SEM micrographs did not reveal any discontinuity. [Copyright &y& Elsevier]