369399 Factors Affecting H2S Desulfurization Performance of ZnO Based Adsorbents for Wide Temperature Applications (20-400C) Effect of COS Formation and Moisture Adsorption on H2S Removal Efficiency

Tuesday, November 18, 2014
Galleria Exhibit Hall (Hilton Atlanta)
Achintya Sujan and Bruce Tatarchuk, Chemical Engineering, Auburn University, Auburn, AL

ZnO based adsorbents have been widely applied for H2S removal in the chemical industry. Formation of COS during desulfurization is influenced by equilibrium reaction between carbon oxides, mainly CO2 and CO, operating condition (feed temperature) and performance of H2S removal sorbent (For instance, ZnS as a catalyst for reaction between CO2 and H2S to form COS). Equilibrium calculations suggest that restricting the feed stream to low operating temperature means avoiding the reaction between CO2 and H2S. However, CO and H2S still react homogeneously to form COS. COS removal is essential to bring down the total sulfur concentration to sub-ppm levels for fuel cell applications. Carbonyl Sulfide (COS) formation during desulfurization process contradicts the aim of desulfurization operation and the formed COS is unfavorable to the downstream process catalysts, equipment and fluid pipelines. H2O is a more polar molecule with a dipole moment of 1.85 Debye as compared to H2S with a dipole moment of 0.97 Debye. The adsorption kinetics of ZnO based sorbents is severely affected in presence of moisture in H2S feed stream containing H2O. However, presence of moisture prevents COS formation due to a shift in the equilibrium reaction between COS and H2O to form H2S and CO2. The current work aims to identify strategies to increase total sulfur capacity of desulfurizer unit on account of the above mentioned phenomena. Strategies such as tandem bed approach consisting of COS hydrolysis catalyst and ZnO sorbent bed and simultaneous H2S and COS removal via adsorption on active carbons, modified ZnO sorbents will be shown.

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