Fundamental Study on Decomposition Characteristics of Mercury Compounds over Solid Powder by Temperature-Programmed Decomposition Desorption Mass Spectrometry

Abstract

Stabilities and/or decomposition characteristics of mercury compounds are important for the design of solid sorbents for mercury vapor removal from coal-derived flue gas and fuel gas. However, available data on the stability and decomposition behavior of mercury compounds are inadequate. The stability and/or decomposition behavior of mercury compounds, such as HgS (metacinnabar and cinnabar), HgO, HgSO4, HgCl2, and Hg2Cl2, were investigated by the temperature-programmed decomposition and desorption technique using a mass spectrometer (TPDD−mass) method. The effects of solid diluents, such as quartz, SiC, Al2O3, TiO2, or activated carbon (AC), on the decomposition characteristics were also studied by the TPDD−mass method. In particular, the stability and reactivity of mercury chloride (HgCl2) in coal combustion flue gas and coal-derived fuel gas conditions were examined. The following results were obtained: (1) the order of the main peak temperature of mercury evolution from the decomposition of the mercury compound diluted with quartz sand in He flow was as follows: HgS (metacinnabar) = HgO < HgS (cinnabar) < HgSO4; (2) HgSO4 was hydrolyzed with H2O; (3) HgO was reduced by SO2 in the presence of H2O and O2; (4) HgCl2 and Hg2Cl2 over SiO2 were more easily decomposed than the other mercury compounds; (5) Among the diluents of HgCl2, SiO2, SiC, Al2O3, TiO2, and AC, HgCl2 was most easily decomposed to Hg0 over SiO2; (6) AC as a diluent apparently stabilizes HgCl2; and (7) HgCl2 gas could be converted to Hg0 over quartz wool, Pyrex wool, ceramic (SiO2−Al2O3) wool, carbon fiber, and AC at high temperatures (>ca. 200 °C).