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

A regenerable sorbent based on manganese oxides impregnated on high surface area ?-alumina and supported onto cordierite honeycomb monolith was tested for elemental mercury capture in different gas environments. Hg capture experiments were carried out in a lab-scale quartz reactor operated at temperatures from 50 °C to 350 °C, Hg concentration in the range 50-250?g/m3, and GHSV=3.6o105 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 worsened the Hg capture performance, while NO did not show any appreciable effect. The effect of all these species appeared to be reversible, i.e. when they were removed from the gas stream, the original sorbent performance was recovered. 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. When HCl was present in the gas stream the sorbent both adsorbed elemental Hg and catalyzed its heterogeneous oxidation giving an overall outstanding performance. During desorption only oxidized mercury was released.