Mechanism of synergistic removal of NO and SO(2) by sodium bicarbonate

Sodium bicarbonate (NaHCO(3)) is considered to be an effective alkaline adsorbent for SO(2) removal and surprisingly, the concentration of NO is significantly reduced along with the generation of NO(2) during its desulfurization. Unfortunately, the mechanism of NO interaction with NaHCO(3), SO(2) and O(2) is ambiguous. In this work, the effects of absorption gas and absorber composition on SO(2)/NO absorption performance were explored, the absorption products were characterized using XPS and SEM, and the Gibbs free energy of the inferred reaction path was calculated based on density functional theory (DFT). The results showed that SO(2) and O(2) synergistically promoted the absorption and removal of NO by NaHCO(3), which could completely remove SO(2) and absorb 90% of NO at 160 °C. Sodium metabisulfite (Na(2)S(2)O(5)) and sodium dithionate (Na(2)S(2)O(6)) were identified as the active substances responsible for efficient NO absorption, and the oxidation of Na(2)S(2)O(5) to Na(2)S(2)O(6) is the controlling step of the NO removal reaction. Specifically, Na(2)S(2)O(5) is an intermediate produced by the reaction of NaHCO(3) with SO(2), and subsequently reacts with O(2) to produce Na(2)S(2)O(6), which releases reactive oxygen species to oxidize NO to NO(2). In addition, when the S/N ratio is greater than 1 and the O(2) content is greater than 5%, both SO(2) and NO can maintain removal efficiency higher than 90%, indicating that the absorption reaction of SO(2) and NO by NaHCO(3) is highly adaptable to the flue gas composition.