Factors influencing the removal of elemental mercury by Mn-AC sorbent in syngas

Activated coke modified with manganese acetate (Mn-AC) was prepared through incipient impregnation and characterized by nitrogen sorption, X-ray photoelecuon spectroscopy (XPS) and X-ray diffraction (XRD). Mn-AC was used as a sorbent in the removal of elemental mercury in a simulated syngas (0.04% H₂S, 20% CO, 30% H₂ and balanced N₂) and the various actors influencing the removal efficiency were investigated in a bench-scale fixed-bed reactor. The results indicated that Mn-AC exhibits excellent Hg⁰ removal capacity at 200 ℃ and 84.3% of Hg⁰ can be removed from the syngas. H₂S present in the syngas can obviously promote the Hg⁰ removal efficiency at high temperature, as H₂S is oxidized to elemental sulfur (S_ad) that provides active adsorption sites for Hg⁰ to form HgS. Both H₂ and CO are unfavorable to mercury removal, as H₂ may deplete the active oxygen in the sorbent surface and CO may react with the active sulfur sites (forming COS). At high temperature, mercury removal is suppressed, which may be attributed to that the interaction between Hg⁰ and active sulfur sites is weakened and reducing capacity of H₂ is strengthened, resulting in the decrease of the active sites for mercury adsorption.