Elemental mercury capture and oxidation by a regenerable manganese-based sorbent: The effect of gas composition

• The Mn-based sorbent is well suited for operation under oxidizing conditions.
• It is less effective in the absence of oxygen (gasification conditions).
• The presence of HCl highly enhances the performance of the sorbent.
• The critical species is SO2 which irreversibly poisons the manganese active phase.

A regenerable synthetic sorbent based on MnOx impregnated on high surface area γ-alumina and supported onto cordierite honeycomb monolith was tested for elemental mercury capture in different gas environments. Hg removal tests were performed in a lab-scale quartz reactor operated at 50–350 °C, with Hg concentration in the range 50–250 μg/m3, and GHSV = 3.6 · 105 h−1. The sorbent was tested in air (reference case), nitrogen and air with added CO2, CO, NO, SO2 and HCl. Results were analyzed in terms of the apparent initial Hg removal rate. In the absence of oxygen, the sorbent gradually deteriorated its performance. Both CO2 and CO moderately and reversibly worsened the Hg capture performance, while NO did not show any appreciable effect. On the other hand, SO2 adversely impacted on the sorbent performance and most importantly the Hg capture capacity was permanently deteriorated. No release of oxidized Hg was observed in tests containing the above components both during adsorption and desorption stages. In the presence of HCl (50 ppm in air) the sorbent both adsorbed elemental Hg and catalyzed its heterogeneous oxidation giving an overall outstanding performance. During desorption only oxidized mercury was released.