Long Term Stability of Composite Pd and Pd-Au Membranes In Actual Syngas Atmosphere

Composite Pd and Pd-Au membranes were prepared and tested in an actual stream of coal derived, but desulfurized, syngas at the National Center for Carbon Capture (NCCC) in Wilsonville, Al, with the purpose of studying the effects of contaminants in the desulfurized syngas on membrane performance. The membranes, with a permeable area of 200 cm², were characterized by thicknesses ranging from 7 to 14 μm, estimated H₂ permeances ranging from 20 to 28 Nm³ m^-2 h^-1 bar^-0.5 and undetectable He leaks before syngas test.

The present composite Pd membranes permeation study in actual coal derived syngas demonstrated the high robustness and excellent physical integrity of composite Pd membranes, and more importantly elucidated the feasibility and reliability of the use of this technology for industrial applications under severe conditions such as medium-high temperatures, high contaminants concentrations and large fluctuations in operating parameters typically observed in industrial processes. The H₂ permeate flux of all membranes remained exceptionally stable in coal derived syngas for over 235 hours at 12.6 bara and 450°C albeit an initial decline and the formation/deposition of coke. A high H₂ purity in excess of 99.89% was achieved for over 200 h in the syngas at 12.6 bara and 450°C representing significant advancement and breakthrough results, never reported before in the pertinent literature for the application of composite Pd membranes in H₂ production from coal gas. The H₂ permeance decline (50 to 60%), which appeared to be partially reversible, occurred in two steps: rapid surface contamination followed by diffusion of contaminants in to the bulk in agreement with the increase in the H₂ permeance activation energy.