Kinetic study of the reactions between chloramine disinfectants and hydrogen peroxide: Temperature dependence and reaction mechanism

摘要

The temperature-dependent kinetics for the reaction between hydrogen peroxide and chloramine water disinfectants (NH_2Cl, NHCl_2, and NCl_3) have been determined using stopped flow-UV/Vis spectrophotom-etry. Rate constants for the mono- and dichloramine-peroxide reaction were on the order of 10~(-2) NT~(-1) s~(-1) and 10~(-5) M~(-1) s~(-1), respectively. The reaction of trichloramine with peroxide was negligibly slow compared to its thermal and photolytically-induced decomposition. Arrhenius expressions of In(k_(H2O2-NH2Cl)) = (17.3 ±1.5)-(51 500 ±3700)/RT and ln(k_(H2O2-NHCl2)) = (18.2 ± 1.9)-(75800±5100)/RT were obtained for the mono- and dichloramine peroxide reaction over the temperature ranges 11.4-37.9 and 35.0-55.0 ℃, respectively. Both monochloramine and hydrogen peroxide were first-order in the rate-limiting kinetic step and concomitant measurements made using a chloride ion selective electrode showed that the chloride was produced quantitatively. These data will aid water utilities in predicting chloramine concentrations (and thus disinfection potential) throughout the water distribution system.