HgCl₂ Calibration Gas Generated by a Solid Oxidant

The generation of gaseous, chlorine-free, and pure HgCl2 calibration gas is a vital technology for the mercury continuous emission monitoring system (Hg-CEMS). Presently, the conventional approaches involve gaseous chlorine sources (Cl-2/HCl) to oxidize Hg-0 or liquid HgCl2 to be evaporated. However, the former inevitably engenders the excessive chlorine species that detrimentally affects the purity of HgCl2, and the latter does not achieve a steady flow rate of HgCl2. In this paper, a new technology was invented that uses the metal chlorides as the chlorine source to oxidize Hg-0 to produce highly pure and precise gaseous HgCl2 calibration gas that can be entirely applied in the Hg-CEMS. The impacts of metal chlorides, carrier materials, agent dosages, and reaction temperatures on the HgCl2 generation efficiency were investigated. The findings demonstrate that the optimal oxidant is CuCl2 as the active component, which is supported by MCM-41 as the carrier with a dosage of 10% in mass. The active component manifests a highly dispersed amorphous state and a crystalline state upon the carrier that are characterized in different activation temperatures. Amorphous state Cu and Cl efficiently oxidize Hg-0 to HgCl2 at 60 degrees C, while crystalline CuCl2 requires a higher activation temperature of 180 degrees C, suggesting a reaction temperature of 180 degrees C that optimally allows the active components to be fully utilized and avoids HgCl2 condensation at a low temperature to ensure the efficiency of the oxidation reaction. HgCl is verified as an intermediate species to form ultimate HgCl2. HgCl is formed by Hg-0 and active chlorine in CuCl2 through the fast chemical reaction, which subsequently produces the resultant HgCl2 by exchanging the electrons with Cu2+ through the Cl atoms.