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

The oxidation rate constants of mercury gas (Hg 0 ) are difficult to determine because Hg 0 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 Hg 0 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 Hg 0 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 cm 6 ·molecules -2 ·s -1 with N 2 as the third body at 297 ± 1 °K. The surface catalyzed reaction on a quartz window was second order, and the rate constant was 2.7 × 10 -17 mL 2 ·molecules -1 ·cm -2 sec. The photoinduced contribution was obtained by comparing the Hg 0 decay rate between continuous and intermittent irradiations. The utilization efficiency of 253.7 nm photons for Hg 0 oxidations at a chlorine concentration of 6.5 × 10 15 molecules·mL -1 was <6.7 × 10 -4 molecules·photon -1 .