Recent Advances in the High Temperature Capture of Elemental Mercury by Inorganic Sorbents: Packed Bed and Flow Reactor Studies

This paper reports on recent results relating to high temperature sorption of metallic mercury on MinPlus sorbent, an inorganic substrate derived from paper recycling residues. Results from a packed bed reactor as well as in-flow dispersed phase reactor are reported. A new type of packed bed was developed, in which 0.3 g sorbent was supported on alumina wool in an alumina lined reactor. Previous results had shown that MinPlus reacts with quartz at high temperatures, thus rendering suspect previous packed bed data that utilized quartz beads and quartz wool for support. The new data show an apparent maximum sorption of Hg at around 900C, at which temperature the bed material shrinks and by-passing occurs. Maximum sorption also occurs immediately after the sorbent has reached its maximum temperature. Thereafter a time dependent process de-activates it. The disperse phase reactor data support the hypothesis that sorption occurs only after the sorbent has been allowed to deposit on the walls for times exceeding the gas mean residence time. Data from both reactors suggest that the free SiO2 content of the sorbent is very important, and that the performance of a poorer sorbent (resulting from changes in the paper composition from which the residue was produced) can be improved through addition of finely divided quartz powder. The data are consistent with a mechanism involving a high temperature solid reaction between CaO and (free) SiO2 to produce a species which scavenges Hg. Spent sorbent samples are currently undergoing analysis to help close the mass balance in the packed bed, and to suggest the nature of the reaction product with mercury. These results are not available now, but will be reported at the conference.