Kinetics of Chlorination of Benzophenone‑3 in the Presence of Bromide and Ammonia

The aim of this study was to assess the impact of chlorination on the degradation of one of the most commonly used UV filters (benzophenone-3 (BP-3)) and the effects of bromide and ammonia on the kinetics of BP-3 elimination. Bromide and ammonia are rapidly converted to bromine and chloramines during chlorination. At first, the rate constants of chlorine, bromine and monochloramine with BP-3 were determined at various pH levels. BP-3 was found to react rapidly with chlorine and bromine, with values of apparent second order rate constants equal to 1.25(±0.14) × 10³ M^–1·s^–1 and 4.04(±0.54) × 10⁶ M^–1·s^–1 at pH 8.5 for <i>k</i>_{Chlorine/BP‑3} and <i>k</i>_{Bromine/BP‑3}, respectively, whereas low monochloramine reactivity was observed (<i>k</i>_{NH₂Cl/BP–3} = 0.112 M^–1·s^–1). To assess the impact of the inorganic content of water on BP-3 degradation, chlorination experiments with different added concentrations of bromide and/or ammonia were conducted. Under these conditions, BP-3 degradation was found to be enhanced in the presence of bromide due to the formation of bromine, whereas it was inhibited in the presence of ammonia. However, the results obtained were pH dependent. Finally, a kinetic model considering 18 reactions was developed using Copasi to estimate BP-3 degradation during chlorination in the presence of bromide and ammonia