Upgrading of a syngas mixture for pure hydrogen production in a Pd-Ag membrane reactor

Water gas shift (WGS) is a thermodynamics limited reaction and CO equilibrium conversion of a traditional reactor is furthermore reduced owing to the presence of H-2 (ca. 50%) in the feed stream coming from a reformer. The upgrading of a simulated reformate stream was experimentally investigated as a function of temperature (280-320 degrees C), feed pressure (up to 600 kPa), gas hourly space velocity (GHSV), etc. using a Pd-alloy membrane reactor (MR) packed with a commercial catalyst CuO/CeO2/Al2O3; no sweep gas was used. The MR performance was also evaluated using new parameters such as conversion index, H-2 recovery and extraction index, etc., which evidence the advantages with respect to a traditional reactor. A Pd-based MR operated successfully overcoming the thermodynamic constraints of a traditional reactor and, specifically, the drawback introduced by the hydrogen presence. In fact, a CO conversion of 90% significantly exceeded (three times) the thermodynamics upper limit (< 36%) of a traditional reactor owing to ca. 80% of hydrogen permeated through the membrane. The overall process performance was significantly improved by the presence of the Pd-based membrane and, thus, by the high reaction pressure which allowed and drove the hydrogen permeation. (C) 2009 Elsevier Ltd. All rights reserved.