NO Removal from Flue Gas Using Conventional Imidazolium-Based Ionic Liquids at High Pressures

Nitrogen oxide (NO) significantly contributes to environmental pollution problems, such as photochemical smog and acid rain. NO absorption in ionic liquids was an attractive issue, but little attention was paid to the removal of NO with a low concentration from coal-fired flue gas. In this work, conventional ionic liquids were used as environmentally benign solvents with low cost compared to functional ionic liquids to separate NO from simulated multi-flue gas mixtures. The concentration of NO is only 1000 ppm. NO removal performance by conventional ionic liquids was investigated on a high-pressure reaction system. Results showed that, among four conventional imidazolium ionic liquids, [Bmim][OAc] and [Bmim][NO3] presented high efficiency for NO removal. NO removal performance is mainly determined by the oxidation rate of NO to NO2 in the presence of O2 and the absorption capacity of NO2 in ionic liquids. High pressure was favored to NO removal efficiency. Both of the oxidation rates of NO and NO2 absorption in ionic liquids were dramatically increased at elevated pressures. This work also provides interesting possibilities for simultaneous removal of SO2 and NO from flue gas. Highly efficient simultaneous removal of SO2 and NO using [Bmim][OAc] was achieved with the removal efficiency of 98.0 and 93.5%, respectively.