Coal-based sulfur hybrid sorbent for removal of Hg0 from flue gas. Part 1. High inorganic sulfur coal

Abstract

A novel sulfur hybrid mercury sorbent was successfully prepared by chemically activating high inorganic sulfur coal using potassium hydroxide (KOH). The optimal conditions for preparing the sorbent are at 800 °C with the ratio of KOH/coal at 2:4 by mass. The prepared sorbent, named ZY-2:4-800, containing 0.92% sulfur with a high specific surface area of 353 m2·g−1, has a wide temperature range for mercury removal. Between 60 and 180 °C, the Hg0 removal efficiencies of this sorbent keep above 95% within 2 hr under N2+O2+NO+SO2+H2O. This is because that O2 can slightly improve the mercury removal ability of the sorbent, and it shows great resistance to acid gas (NO and SO2) and H2O. The calculated Hg0 adsorption capacity of ZY-2:4-800 is 214.7 μg·g−1, which is much higher than that of activated carbon sorbent (ACs) reported in the literature. Based on XPS and Hg-TPDD analysis, it is revealed that the iron sulfide compounds in coal can be converted into active sites as S0, S22–, and C-S during the preparation of the sorbents, and Hg interacts with these active sites and forms β-HgS (metacinnabar). The excellent mercury removal performance and the low cost indicate that the as-prepared sorbent from the blend of the high inorganic-sulfur coal and KOH is a promising sorbent for mercury removal from flue gas. It is expected that this method could be applicable in converting other high-inorganic sulfur coals into efficient mercury sorbents.