(457b) Novel Sorbents for Wide Temperature H2S /COS Removal in Fuel Cell Applications

High efficiency desulfurization is critical to maintain the activity of fuel processing catalysts and high value membrane electrode assemblies in fuel cell systems. Various researches for H2S removal have been reported in details, however, removal of COS is not concerned yet as much as H2S, because COS is not the major sulfur compound produced from gasification. In addition, the removal of COS is more difficult than H2S, since COS is inactive compared to H2S, probably resulting from its neutrality and similarity to CO2. What is worse, COS is sometimes, produced through the reaction of H2S and CO2/CO. The objective of the present work is to develop supported doped sorbents for efficient removal of H2S and COS over wide temperature range, also inhibit the formation of COS, so that desulfurization process is cost-effective, scalable and the sorbent is regenerable over higher number of duty cycles without significant loss in activity.

Promoted ZnO/SiO2 sorbents with formulation Mx/2Nx/2ZnO (1-x)/SiO2 where (M, N = Mn, Fe, Co, Ni, Mg, Cu) and 0≤x≤1, were prepared by incipient wetness impregnation method. Three different challenge gas compositions were chosen as a) 1 vol% H2S/H2 b) 1% COS/N2 and c) 1% H2S,33% CO/CO2 and balance H2¬, to specifically screen sorbents that a) remove H2S b) remove COS and c) inhibit COS formation, respectively. The adsorption was studied in a packed bed design in the temperature range of room temperature to 400 C in both dry and moist conditions. The un-promoted ZnO/SiO2 shows 5-12 fold increase in H2S saturation capacity over commercial ZnO extrudates. On doping the sorbent with 5 mol % Cu, H2S capacity further goes up by 30%. Transient COS is not detected in the reaction products, if desulfurization is done at room temperature with doped sorbents. The Cu0.05ZnO0.95/SiO2 sorbent shows >70% capacity recovery when regenerated over 10 cycles in air.

Novel bimetallic doped sorbents with the formulation M0.025N0.025ZnO0.95/SiO2 showed >90% metal utilization for sulfur adsorption capacities in comparison to single dopant sorbents M0.05ZnO0.95/SiO2 at room temperature. Layered bed design, with H2S and COS specific sorbent to eliminate trace amounts of sulfur, is adopted. Furthermore, a novel composite bed design is developed, with glass-fiber entrapped sorbent as polishing layer that offers advantages of low pressure drop and higher sulfur adsorption.

Keywords: H2S removal, COS mitigation, COS inhibition, dopants, Microfibrous entrapment.