Method for the Study of Gaseous Oxidants for the Oxidation of Mercury Gas

The oxidation rate constants of mercury gas (Hg0) are difficult to determine because Hg0 easily adsorbs on reactor walls and the reactions can be catalyzed by the solid surface. Also, the UV light which is commonly used to monitor the Hg0 concentration can accelerate the reaction. We have demonstrated a procedure that allows the determination of gas-phase, surface-catalyzed, and photoinduced contributions in the kinetic study of the reaction of Hg0 with chlorine gas. By experimenting with several reactors having different surface-to-volume ratios, the relative contributions of gas-phase and surface-catalyzed reactions were determined. The pressure-dependent study revealed that the gas-phase oxidation was by means of a three-body collision process. The third-order rate constant was determined to be 7.5 (?0.2) * 10^-39 cm6?molecules-2?s-1 with N2 as the third body at 297 ? 1 (degree)K. The surface catalyzed reaction on a quartz window was second order, and the rate constant was 2.7 * 10^-17 mL2?molecules-1?cm-2 sec. The photoinduced contribution was obtained by comparing the Hg0 decay rate between continuous and intermittent irradiations. The utilization efficiency of 253.7 nm photons for Hg0 oxidations at a chlorine concentration of 6.5 * 10^15 molecules?mL-1 was <6.7 * 10^-4 molecules?photon-1.