Study on DeNOx of NaClO2 in simulated seawater solution enhanced by hydrodynamic cavitation

Abstract

Ship exhaust causes significant air pollution, and NOx is one of the most challenging pollutants to remove. In this study, we propose a novel method for denitrification (DeNOx) using NaClO2-simulated seawater solution enhanced by hydrodynamic cavitation. We investigate the impact of initial solution pH, temperature, NaClO2 concentration, and the inlet pressure of the hydrodynamic cavitation reactor on DeNOx efficiency. The results indicate that under optimal conditions, a 100 % DeNOx efficiency can be achieved with a NaClO2 concentration of 0.1 mmol/L. Cavitation enhances mass transfer by generating microjets and increasing the gas–liquid contact area. The oxidation of NO and NO2 by hydroxyl radicals and chlorine oxygen radicals produced through cavitation could potentially enhance NOx removal efficiency. The presence of dissolved salts in simulated seawater might boost cavitation activity by reducing vapour pressure and increasing interfacial tension, leading to the more robust collapse of cavitation bubbles and thereby reinforcing cavitation effects. In addition, the multiple reactive inorganic chlorinated radicals (Cl, HClO / ClOH·-, Cl2·-) formed in simulated seawater due to the presence of Cl- might also play an essential role in DeNOx. This study demonstrated that the DeNOx by NaClO2 in simulated seawater enhanced by hydrodynamic cavitation was a promising option for NOx removal, especially for ocean-going vessels.