Integrated SO2–NOX–CO2 Removal from Simulated Ship Exhaust by a Two-Stage NaClO/NaOH Oxidation–Absorption Process: Apparent Kinetics and Pollutant Interactions

Stringent ship-emission regulations require integrated control of SO2, NOX, and CO2. This study evaluated a two-stage NaClO/NaOH oxidation–absorption process for simulated ship exhaust using standard-state thermodynamic calculations, area-normalized macroscopic apparent kinetics, and continuous scrubbing experiments. The selected reaction pathways were thermodynamically favorable. In the NaClO stage, the apparent depletion behavior followed SO2 > NO >> CO2, with apparent reaction orders of 0.885, 0.698, and 1.000, respectively, indicating preferential SO2 removal and NO oxidation, while CO2 capture depended mainly on downstream alkaline absorption. The effect of SO2 on NO was concentration-dependent: NO depletion increased at low-to-moderate SO2 loadings but declined at higher loadings, consistent with a shift from promoting sulfur–nitrogen interactions toward stronger competition for oxidant. Increasing second-stage NaOH concentration and liquid flow rate mainly improved CO2 and NOX removal. Under the selected condition of 60 g L−1 NaOH and 600 mL min−1 liquid flow, SO2, NO, NOX, and CO2 removals reached 99.7%, 98.2%, 94.3%, and 88.9%, respectively. CO2-containing feeds reduced total NOX removal with little effect on NO removal, indicating competition for downstream alkaline capacity. These results clarify stage-specific pollutant interactions and provide an experimental basis for integrated marine exhaust treatment.