Kinetics and mechanisms of H2S adsorption by alkaline activated carbon

Activated carbon adsorption is widely used to remove hydrogen sulfide (H2S), one of the major odorous compounds, from gas streams. In this study, the mechanisms of H2S adsorption by alkaline activated carbon were systematically studied. Two brands of commercial activated carbons were used as H2S adsorbents. A series of designed experiments were carried out to understand on a fundamental basis the differences in H2S removal capacity observed for the two types of carbons and samples for the same carbon obtained from different batches. The physicochemical and structural characteristics of the original and exhausted activated carbons were identified using several analytical approaches (i.e., XRF, SEM, XRD, and BET). The relationships between the adsorption performances of activated carbon for H2S and its physicochemical characteristics were discussed. The kinetics of the H2S adsorption was also studied using TGA/DSC system. Both physical adsorption and chemisorption played an important role in the H2S adsorption mechanisms with the studied carbons. Chemisorption was rapid and occurred mostly at the carbon surface whereas physical adsorption was relatively slow and mostly took place at the inner pores of carbon. Carbon II demonstrated the best performance of H2S removal due to its high capacity of both physical adsorption and chemisorption. Catalytic effects of transition metals might also contribute to enhancing the H2S oxidation.