Kinetics of Nitric Oxide Absorption from Flue Gas Using an Advanced Oxidation Process with Sodium Persulfate Solution

Wet scrubbing is an effective nitric oxide (NO) emission control technology for marine diesel engines. Sodium persulfate (Na2S2O8) can efficiently oxidize NO and promote the absorption of NO. The activation of Na2S2O8 could enhance the mass transfer process of NO. However, the reaction kinetic mechanism of this method remains unclear, which was investigated through a bubble column reactor in this paper. The effects of several parameters on the NO absorption rate were tested with the gas flow rate of 0.8 L/min and the absorber volume of 1.0 L at 1 atm. It was found that the NO absorption rate was promoted gradually with the increase of the Na2S2O8 concentration (0.01-0.15 mol/L), NO inlet concentration (400-1200 ppm), and temperature (303-343 K). The NO absorption rate increased by 137.00% and then decreased by 1.05% as the pH value increased from 7 to 10 and then rose to 12, while the pH in the acidic solution had little effect on the nitric oxide absorption rate. In addition, during the oxidation of NO, the activation of Na2S2O8 could generate sulfate radicals (SO4 center dot- ) and hydroxyl radicals (OH center dot), which would significantly increase the NO absorption rate due to the strong oxidizing nature of free radicals. Simulation results showed that the absorption process is a pseudo-0.6-order for NO and a pseudo-0.15-order for Na2S2O8. The mass transfer process, especially the gas phase mass transfer, was the main rate-determining step for the NO absorption and the location of the reaction was the liquid film. Moreover, the established NO absorption model is in good agreement with the experimental results. It illustrated that the Na2S2O8/seawater system shows great application potential in marine exhaust gas purification.