Absorption of Nitrogen Oxides into Sodium Hydroxide Solution in a Rotating Packed Bed with Preoxidation by Ozone

This study employed a rotating packed bed (RPB) to enhance the absorption performance of nitrogen oxides (NO x ) into sodium hydroxide (NaOH) solution with the preoxidation of NO by ozone. The absorption performance of NO x was evaluated in terms of its removal efficiency (η) from a gas stream under various operating conditions including O 3 /NO x molar ratio (MR), rotation speed of the RPB ( N ), liquid flow rate ( L ), NaOH concentration ( C NaOH ), inlet NO x concentration ( C NO x ), and using time ( t ). Also, the corresponding effect of adding oxidants (NaClO, H 2 O 2, and KMnO 4 ) and a reductant (CO(NH 2 ) 2 ) into the NaOH solution on NO x removal efficiency was investigated. Results indicated that preoxidation of NO by O 3 significantly improved NO x removal efficiency and the removal efficiency increased with increasing O 3 /NO x molar ratio, NaOH concentration, and liquid flow rate but decreased with increase in inlet NO x concentration and using time. Additionally, NO x removal efficiency first increased and then decreased with increasing rotation speed of the RPB. Both the oxidation and reduction additives enhanced NO x removal efficiency, and the order of enhancement was found to be KMnO 4 > H 2 O 2 > CO(NH 2 ) 2 > NaClO. These results further indicate that the hydrolysis reactions of NO x are the rate-determining steps in the NO x absorption process and, thus, the main factors hindering NO x removal during the wet scrubbing process. This work demonstrates that RPB has great potential for removal of NO x by a wet scrubbing process in view of the small size of the RPB, low temperature, and the short gas retention time of 0.27 s applied in this work.