Induced synthesis of SO2-promoting and H2O-tolerant sorbents for elemental mercury removal from flue gas

Abstract

In this study, novel S-doped sorbents synthesized via one-step co-pyrolysis of biomass and scrap tires under SO2 atmosphere were developed for elemental mercury (Hg0) removal from coal-fired flue gas. The presence of SO2 could regulate the sulfur species in S-doped sorbents and improve their Hg0 removal performance. Sample characterization exhibited that SO2 activation increased the sulfur content and decreased the carbon content in sorbents due to the occurrence of carbothermal reduction reaction. The specific surface area, pore volume, and micropore content in S-doped sorbents were obviously improved compared with raw sorbents. After SO2 activation, partial inorganic sulfide was converted into sulfur-containing functional groups and more oxygen-containing functional groups were generated on the sorbents. The S-doped sorbents presented more excellent performance for Hg0 removal compared with raw sorbents. The optimal pyrolysis temperature and SO2 concentration in activation atmosphere were 700 °C and 10%, respectively. It was surprising that SO2 facilitated Hg0 removal and the S-doped sorbents showed good water-resistance due to the presence of ZnS. O2 and NO had positive effects on Hg0 removal. A close fitting to the pseudo-second-order model was obtained for the behavior of Hg0 removal over S-doped sorbents. Aliphatic sulfur, sulfoxide, carbonyl and carboxyl/ester groups functioned as active components for Hg0 removal.