Desulfurization of digester gas: prediction of activated carbon bed performance at low concentrations of hydrogen sulfide

Three chemically modified/impregnated activated carbons (supplied by manufactures) were used for adsorption-catalytic removal of hydrogen sulfide from digester gas. The performance of samples was studied in dynamic conditions at 1000, 2000 and 5000 ppm of H2S in digester gas. The results showed differences in the H2S removal capacities related to the type of carbon and conditions of the experiment. A decrease in H2S concentration resulted in an increase in a breakthrough capacity, which is linked to slow kinetics of oxidation process. No significant changes were observed when the oxygen content increased from 1 to 2% and the temperature from 38 to 60 °C. On the surface of carbons studied hydrogen sulfide was oxidized predominantly to sulfur, which was deposited in micropores, either on the walls or at the pore entrances. The capacities at low concentrations, 50 and 100 ppm, of H2S were determined using an approach based on known theoretical solution of a dynamic model where the parameters of the model were determined from the experimental data at a high concentration of an adsorbate.