(154f) Carbonyl Sulfide Removal From Fuel Reformates At Ambient Conditions During Hydrogen Production for Fuel Cells

PEMFCs operated at low to ambient temperatures in vehicular applications are gaining interest as the ambient temperature operation offers an advantage of lower pressure drop due to lower viscosities of the gas fed to the electrodes. Post reformer desulfurization is an important unit operation in fuel processing of hydrocarbon during the hydrogen production for PEMFCs. The major sulfur species in the reformate stream is H₂S and is effectively removed by ZnO based adsorbents. However, in addition to H₂S the reformate streams with low moisture content also contain considerable amount of CO, CO₂. At ambient conditions, the Carbonyl Sulfide (COS) formation occurs via the homogeneous reaction between CO and H₂S in the reformate stream. COS is less acidic and less polar than H₂S and ZnO is not efficient for removal. However, COS removal is essential to bring down the total sulfur concentration to sub-ppm levels for fuel cell applications. The total sulfur breakthrough on ZnO based adsorbents is determined by homogeneous COS formation (CO+H₂S) at low water concentrations. Even with hydro-treating, COS removal is particularly problematic as thermodynamic constraints dictate only partial conversion of COS to H₂S. COS is also formed via heterogeneous reactions between CO₂ and sulfided ZnO based sorbents. The focus of the current work is to understand the various circumstances under which COS formation takes places over wide temperature range (25°C – 400°C) in a simulated reformate stream with significant CO, CO₂ followed by a sorbent approach with several high surface area supports like SiO₂, TiO₂, Al₂O₃, PICA Carbon, ZrO₂ or in presence of moisture catalytically hydrolyze COS into H₂S which may then be removed by an efficient ZnO based sorbent (>0.5 gS/g sorbent).