Comparison of various chemical compounds for the removal of SO₂ and NO_x with wet scrubbing for marine diesel engines

Seawater, NaOH, NaClO, NaClO₂, H₂O₂, and KMnO₄ were used as scrubbing liquids to react with SO_x and NO_x separately in a customized wet scrubber. The absorption of SO₂ in the aqueous phase was influenced by three factors: pH, ionic concentration, and oxidation potential. For NO_x removal, the effectiveness of various chemical compounds can be ranked from least to most effective as follows: seawater, NaOH, H₂O₂ < NaClO < KMnO₄ < NaClO₂. This effectiveness was influenced by the chemical compound's ability to oxidize NO to NO₂, absorb the NO₂ that was formed, and retaining the nitrogen in the aqueous phase. High oxidation potential promoted the oxidation of NO to NO₂ but hindered the absorption of NO₂. NaClO₂ was superior compared to NaClO in all three categories of oxidizing, absorption and retention. NaClO could not retain a significant amount of NO₂ which it absorbed in the aqueous phase. The pH around 8 provided a good balance between oxidation versus absorption/retention and reactant utilization for the chlorine-based oxidants. KMnO₄ had the lowest reactant consumption rate; only half a mole was consumed for every mole of NO removed, compared to around 2-3 mol of chlorite or 3-5 mol of hypochlorite.