Removal of Nitric Oxide and Sulfur Dioxide from Flue Gas Using a Hexamminecobalt(II)/Iodide Solution

Abstract

An innovative catalyst system has been developed to simultaneously remove NO and SO2 from combustion flue gas. Such a catalyst system may be introduced to the scrubbing solution using ammonia solution to accomplish sequential absorption and catalytic oxidation of both NO and SO2 in the same reactor. When the catalyst system is utilized for removing NO and SO2 from the flue gas, Co(NH3)62+ ions act as the catalyst and I- as the cocatalyst. Dissolved oxygen, in equilibrium with the residual oxygen in the flue gas, is the oxidant. The overall removal process is further enhanced by UV irradiation at 360 nm. More than 95% of NO is removed at a feed concentration of 250−900 ppm, and nearly 100% of SO2 is removed at 800−2500 ppm. Increasing SO2 concentration in the feed gas results in higher NO removal efficiency. The optimal temperature for the NO removal is found about 50 °C. The best treatment results are obtained at an optimal I-/Co2+ with a concentration ratio of 0.25. The NO removal rate also increases with the feed gas oxygen concentration up to 5.2%. Br- was a less effective cocatalyst than I-. NO and SO2 can be converted to ammonia sulfate and ammonia nitrate that can be used for manufacturing fertilizers. The process described here demonstrates the feasibility of removing SO2 and NO simultaneously only by retrofitting the existing wet flue-gas-desulfurization (FGD) scrubbers.