SO2 resistance of CeO2- and Co3O4-supported activated carbon during removal of mercury from flue gas: A comparative study

Abstract

How to enhance the SO2 tolerance of transition metal oxide-supported activated carbon is one of the hottest issues in the field of mercury capture from flue gas. Addition of a foreign metal ion to prepare bimetallic adsorbent is a common method of improving the SO2 tolerance of adsorbent. However, this approach suffers from high cost and a complex preparation process. In this study, CeO2- and Co3O4-supported activated carbon (m%CeO2/AC and m%Co3O4/AC), with various loading values of active center, were prepared by an incipient wetness impregnation method, and their SO2 tolerances were compared. The mercury removal performance and SO2 tolerance of both CeO2/AC and Co3O4/AC could be remarkably improved through increasing the loading amount of the active center. Co3O4/AC exhibited high affinity with SO2, and the chemisorbed oxygen in Co3O4 would be largely consumed, when SO2 was present in the flue gas, resulting in a significant decrease of mercury removal efficiency. The mercury removal efficiencies of 20%CeO2/AC, 40%CeO2/AC and 60%CeO2/AC were 86.1%, 93.7% and 93.7%, respectively, during removal of mercury from flue gas at 150 °C in the presence of SO2. 20%CeO2/AC was the optimal adsorbent for mercury capture from flue gas, owing to its excellent mercury removal efficiency, strong SO2 tolerance and relatively lower cost. The mercury species formed over spent 20%CeO2/AC were HgO and HgSO4. The HgO was generated through the reaction of mercury and chemisorbed oxygen, while the formation of HgSO4 was due to the reaction between mercury, SO2 and chemisorbed oxygen. The regeneration investigation indicated that the activity of spent 20%CeO2/AC could be almost fully recovered through a temperature-programmed decomposition and desorption process. The present study showed that the SO2 tolerance of CeO2/AC could be easily improved through regulation of the loading amount of the active center.