S. Liguori

Performance and Long-Term Stability of Pd/PSS and Pd/Al2O3 Membranes for Hydrogen Separation

The present work is focused on the investigation of the performance and long-term stability of two composite palladium membranes under different operating conditions. One membrane (Pd/porous stainless steel (PSS)) is characterized by a ~10 µm-thick palladium layer on a porous stainless steel substrate, which is pretreated by means of surface modification and oxidation; the other membrane (Pd/Al2O3) is constituted by a ~7 µm-thick palladium layer on an asymmetric microporous Al2O3 substrate. The operating temperature and pressure ranges, used for studying the performance of these two kinds of membranes, are 350–450 °C and 200–800 kPa, respectively. The H2 permeances and the H2/N2 selectivities of both membranes were investigated and compared with literature data. At 400 °C and 200 kPa as pressure difference, Pd/PSS and Pd/Al2O3 membranes exhibited an H2/N2 ideal selectivity equal to 11700 and 6200, respectively, showing stability for 600 h. Thereafter, H2/N2 selectivity of both membranes progressively decreased and after around 2000 h, dropped dramatically to 55 and 310 for the Pd/PSS and Pd/Al2O3 membranes, respectively. As evidenced by Scanning Electron Microscope (SEM) analyses, the pinholes appear on the whole surface of the Pd/PSS membrane and this is probably due to release of sulphur from the graphite seal rings.

Hydrogen Production by Ethanol Steam Reforming: Experimental Study of a Pd-Ag Membrane Reactor and Traditional Reactor Behaviour

In this experimental work, the ethanol steam reforming reaction for producing hydrogen was studied in both a traditional reactor (TR) and a Pd-Ag dense membrane reactor (MR). Both reactors have been packed with a commercial Ru-based catalyst. The experimental tests have been performed in the temperature range 400-500 °C and in the pressure range 2.0-3.6 bar.The results are reported in terms of ethanol conversion, hydrogen production, product selectivities and hydrogen recovery (for the MR only). It has been found that the MR is able to increase the ethanol conversion as well as increase the hydrogen production with respect to a traditional reactor. Moreover, part of the hydrogen produced in the MR is recovered as a CO-free hydrogen stream and is suitable for feeding a PEM fuel cell system.