Continuous Generation of HgCl2 by Dielectric Barrier Discharge Nonthermal Plasma. Part II: Influences of the Cl Source

This study is the first investigation on the effects of the Cl source on Hg-0 oxidation by dielectric barrier discharge (DBD) nonthermal plasma technology in a self-developed DBD reactor under atmospheric pressure. It was found that the initial Hg-0 concentration had no effect on the chlorination reaction in the DBD process. The temperature increased with the increase of the discharge voltage when HCl/Cl(2 )was used as the oxidative radical source. High temperature inhibited the Hg-0 chlorination reaction during the DBD process. The temperature increased from 55.7 to 182.1 degrees C as the discharge voltage increased from 16 to 22 kV when 50 ppm HCl was added, correspondingly, the HgCl2-generation efficiency dropped from 85 to 56.4%. A cooling system was conducive to decrease the side effect of the temperature increase, thereby increasing the HgCl2-generation efficiency. The experimental results showed that using Cl-2 as the Cl source, a higher HgCl2-generation efficiency was achieved at same discharge voltage and concentration compared with HCl as the Cl source, which may be explained by the fact that Cl-2 alleviates the negative effect of temperature. Up to 95% HgCl2 generation efficiency was achieved when 10 ppm Cl-2 was injected in the discharge voltage window of 16 to 22 kV. To avoid the corrosion effect of Cl-2 on the system, mixed Cl-2 and HCl as the Cl source was investigated. The results showed that over 95% HgCl2-generation efficiency was achieved under the injection of 1.25 ppm Cl-2 and 50 ppm HCl at a discharge voltage of 16 kV. This combination of Cl-2 and HCl as the Cl source for the DBD process can serve as a new effective method to generate HgCl2 continuously and has great potential for application in the mercury continuous emission-monitoring system calibrator.