Carbonyl Sulfide (COS) formation during post-reformer desulfurization is an undesired side reaction between residual H2S and CO/CO2 from outlets of Steam Methane Reformers (CH4 + H2O = CO + 3H2), Oxidative Methane Reformers (CH4 + 1/2O2 = CO + 2H2) and Water Gas Shift (CO + H2O = CO2 + H2) reactors. COS is known to poison downstream fuel processor catalysts and equipment. The goal of this work is to assess the promotional effect of Cu dopant in Cu-ZnO/SiO2 sorbents in terms of COS formation characteristics as a function Cu:Zn molar ratio, moisture and temperature at constant H2S partial pressure in a simulated reformate. In the current investigation, COS formation was examined in the temperature range of ambient (22°C) to 400°C on ZnO/SiO2 (21% ZnO loading) and Cu-ZnO/SiO2 (Cu:Zn Molar Ratio = 5:95 and total oxide loading CuO + ZnO = 21% by weight) sorbents during desulfurization of a stream containing 30%CO, 30% CO2, 0.6% H2S and Balance H2. Homogeneous gas phase reaction occurred between H2S and CO/CO2 in the feed stream operated at 400°C and higher. However, no COS was detected at the outlet when the feed was &lt;100°C. At temperature of 200°C and higher COS formation and subsequent breakthrough occurred on both sorbents. Regardless of temperature, COS formation levels were lower in case of Cu-ZnO/SiO2 sorbent as compared to ZnO/SiO2. The lower COS concentration detected in the case of Cu-ZnO/SiO2 was attributed to the catalytic hydrogenation of COS (at 200°C and higher) on Cu2S (formed by reduction with H2S on spent Cu-ZnO/SiO2) as per the following reaction: COS + Cu2S = CO + 2CuS 2CuS + H2 = H2S + Cu2S When experiments were carried out with 5000 ppm moisture present (H2S:H2O ratio ~ 1) in the feed, results indicate much lower levels of COS concentration at saturation observed on both sorbents. Moisture had a COS inhibition effect most likely due to hydrolysis of COS (in this case, ZnS is known to be a catalyst) COS + H2S = H2O + CO2

Carbonyl sulfide formation during wide temperature reformate desulfurization on ZnO/SiO2 and Cu promoted ZnO/SiO2 adsorbents

249th National Meeting (2015)

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