A novel High-Gravity AOP process for enhanced NOx attenuation using alkaline H2O2 as a strong oxidizing reagent: Reaction mechanisms and kinetics

A novel High-Gravity Advanced Oxidation Process (HiGee-AOP) using basic H2O2 solution as a liquid oxidizing reagent was examined for enhanced NOx removal efficiency in this study. At ambient temperature and optimal conditions, the process achieved a 99% removal of the inlet 1000 ppm NO. Spectroscopic experiments and radical-quenching tests indicated that the nucleophilic hydroperoxyl anion (-OOH) dissociated from H2O2 was the strongest reactive oxygen species (ROS) responsible for NO oxidation in alkaline H2O2, producing peroxynitrite (ONOO-) as detected by Fluorescence Spectroscopy. A mass transfer model coupling the reaction kinetics and gas diffusion under high liquid-film renewal conditions was established to simulate the HiGee-AOP process for NO absorption, and it achieved a model-prediction accuracy of within 10% of experimental data. It is speculated that the improved NO removal efficiency by the HiGee-AOP/alkaline H2O2 process stems from the enhanced mass transfer of NO in the heterogeneous reaction system provided by HiGee and the strong affinity of OOH to NO. Oxidation of NO by OOH may proceed first to form the [NO center dot center dot center dot OOH](-) intermediate due to a strong nucleophile-electrophile interaction, which is followed by an electron transfer within the intermediate producing ONOO- and ultimately as nitrate.