This work describes the application of porous metal supported Pd-membranes to the water-gas shift catalytic membrane reactor in the context of its potential application to the Integrated Gasification Combined Cycle (IGCC) process. The objective of this work was to develop a better understanding of Pd-membrane fabrication techniques, water-gas shift catalytic membrane reactor operation, and long-term behavior of the Pd-membranes under water-gas shift conditions. Thin (1.5 - 16 um) Pd-membranes were prepared by electroless deposition techniques on porous metal supports by previously developed methods. Pd-membranes were installed into stainless steel modules and utilized for mixed gas separation (H2/inert, H2/H2O, dry syngas, and wet syngas) at 350 - 450C and 14.5 atma to investigate boundary layer mass transfer resistance and surface inhibition. Pd-membranes were also installed into stainless steel modules with iron-chrome oxide catalyst and tested under water-gas shift conditions to investigate membrane reactor operation in the high pressure (5.0 - 14.6 atma) and high temperature (300 - 500C) regime. After the establishment of appropriate operating conditions, long-term testing was conducted to determine the membrane stability through He leak growth analysis and characterization by SEM and XRD. Pd and Pd/Au-alloy membranes were also investigated for their tolerance to 1 - 20 ppmv of H2S in syngas over extended periods at 400C and 14.0 atma. Water-gas shift catalytic membrane reactor operating parameters were investigated with a focus on high pressure conditions such that high H2 recovery was possible without a sweep gas. With regard to the feed composition, it was desirable to operate at a low H2O/CO ratio for higher H2 recovery, but restrained by the potential for coke formation on the membrane surface, which occurred at a H2O/CO ratio lower than 2.6 at 400C. The application of the Pd-membranes resulted in high CO conversion and H2 recovery for the high temperature (400 - 500C) water-gas shift reaction which then enabled high throughput. Operating at high temperature also resulted in higher membrane permeance and less Pd-surface inhibition by CO and H2O. The water-gas shift catalytic membrane reactor was capable of stable CO conversion and H2 recovery (96% and 88% respectively) at 400C over 900 hours of reaction testing, and 2,500 hours of overall testing of the Pd-membrane. When 2 ppmv H2S was introduced into the membrane reactor, a stable CO conversion of 96% and H2 recovery of 78% were observed over 230 hours. Furthermore, a Pd90Au10-membrane was effective for mixed gas separation with up to 20 ppmv H2S present, achieving a stable H2 flux of 7.8 m3/m2-h with a moderate H2 recovery of 44%. The long-term stability under high pressure reaction conditions represents a breakthrough in Pd-membrane utilization.

" This work investigated the long-term stability of sulfur tolerant Pd/Cu alloy membranes for hydrogen separation by performing characterizations lasting several thousand hours in H2, He and H2S/H2 atmospheres ranging in concentration from 0.2 – 50 ppm and temperatures ranging from 250 - 500ºC. Two methods were used for fabricating the Pd/Cu membranes so that the sulfur tolerant fcc alloy would remain on the surface and minimize the decrease in hydrogen permeance inherent with fcc Pd/Cu alloys. The first method consisted of annealing a Pd/Cu bi-layer at high-temperatures and the second consisted of depositing a Pd/Cu/Pd tri-layer with an ultra-thin surface alloy. High temperature X-ray diffraction (HT-XRD) was employed to study the kinetics of the annealing process and atomic adsorption spectroscopy (AAS) was used to investigate the kinetics of the Cu deposition and Pd displacement of Cu. Upon the introduction of H2S, the permeance decrease observed was dependent upon the H2S feed concentration, and not the time of poisoning. However, after the recovery in pure H2 there was a portion of the permeance which could not be recovered due to adsorbed sulfur blocking H2 adsorption sites. The amount of recoverable permeance was dependent on the time of exposure to H2S and reached a limiting value which decreased with temperature. X-ray photoemission spectroscopy (XPS) was used to investigate poisoned samples and it was observed that the permeance not recovered at a given temperature in H2 was caused mostly by Cu sulfides. Both bi-layer and tri-layer membranes had hydrogen permeances which were higher than homogeneous Pd/Cu membranes of the same surface concentration. However, the tri-layer membranes performed as well as Pd membranes thus eliminating the disadvantage of alloying Pd with Cu without sacrificing sulfur tolerance. "