A comprehensive performance assessment study of pilot-scale Pd and Pd/alloy membranes under extended coal-derived syngas atmosphere testing

Abstract

The present study encompasses the results of a comprehensive performance assessment of different pilot-scale Pd/Alloy composite asymmetric membranes under long-term coal-derived syngas atmosphere testing. The membranes were developed and tested first at the CIMS-WPI laboratory under pure H 2 and later at NCCC under a mixture of N 2 /H 2 and H 2 enriched syngas coming from a TRIG TM gasification system. Thirteen membranes were examined for 4275 h and classified in four types: Pd, Pd/Au, Pd/Pt and Pd/Au/Pt membranes. Their respective H 2 permeance and purity profiles, permeance difference under pure hydrogen and syngas conditions as well as stability of operation were assessed. The membranes showed good stability in syngas although exhibiting an initial drop in permeance when compared to that under pure hydrogen. Pure Pd membranes displayed the highest permeability, but showed pinholes after being exposed to syngas. Pd/Pt membranes showed a reduced permeance drop under syngas conditions, indicating sulfur resistance properties. Furthermore, Pd/Au/Pt membranes, presented for the first time in the literature, displayed stable permeance and purity profile. The inhibition of the initial permeance drop and the long-term operation of these ternary membranes were demonstrated. Finally, Pd/Au membranes were shown to display the most stable permeance and purity characteristics. In this case, the initial permeance drop was significantly reduced, exhibiting the lowest decline amongst all cases considered. It is hypothesized that Au may act as a patch paste blocking defects on the Pd layer.

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“…Furthermore, there is an overall increase in the gold content of the membrane, which can significantly influence the solubility of H 2 in the active sites of the membrane, as reported by Sonwane et al [41]. Nonetheless, the H 2 permeance of the membrane is in agreement with the values presented in the literature for Pd and Pd/Au membranes [9,10,42] and with 20 lm free standing foils, which have a theoretical permeance of 15 and 23 Nm 3 m À2 h À1 bar À0.5 at 350°C and 450°C, respectively. Notice that the resistance of the support is not taken into consideration for the theoretical calculation of the free standing foils, suggesting that the selective layer of the membrane presented in this work has enhanced properties and/or the resistance of the support is negligible.…”

“…The membrane showed a good thermal stability since, after activation, no He leak was found on the membrane at a pressure difference of 1 bar, while the H 2 flux remained stable. This phenomenon as described by Mardilovich et al [9] could be the result of Au acting as a patch paste on the membrane defects.…”

“…In addition, gold was deposited on the surface of the membrane through conventional electroplating. Gold was chosen as the alloy of the membrane since it has been shown to improve the stability and lifetime of Pd membranes under harsh conditions [9]. The thickness of the Pd and Au layers were estimated through gravimetric measurements while its effectiveness was determined through He leak tests.…”

“…In particular palladium-based membranes have been studied as a component of CMR technology since they produce high H 2 fluxes at theoretically infinite H 2 selectivities. Different Pd and Pd-alloy membranes have been tested under industrial conditions, displaying an excellent performance [9,10] suitable for their application in large-scale settings. Through the use of Pd-membranes, the constant removal of H 2 from the reaction zone is possible, altering the composition inside the system and thus allowing higher conversions.…”

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“…Mardilovich et al determined that the transport rate of hydrogen in the synthesis gas in PdAu, PdPt and PdAuPt membranes was higher than that in the pure Pd membrane. While dilatations were observed in the pure Pd membrane after hydrogen permeability, hydrogen permeability values in PdAuPt membranes did not vary even after 4275 hours of test [9]. Lu et al covered alumina supports with a PdNi membrane layer using the electroless plating technique.…”