Multi-stage semi-coke activation for the removal of SO2 and NO

The objective of this work was to find the optimal preparation methods of semi-coke and investigate the absorption mechanisms in the removals of SO2 and NOx. Semi-cokes, treated by different combined activation methods, were used to remove SO2 and NO from simulated flue gas in a fixed bed. Detailed characterizations were discussed by BET, SEM and FTIR. Results showed the activated and loaded semi-cokes had better pore structures with more micropores and mesopores. Activated semi-coke had more reactive oxygen groups, including quinines and conjugated ketones while loaded oxides covered some active sites. The physical and chemical properties both acted in the desulfurization and denitration process. Physisorption dominates over chemisorption at low temperatures in the SO2 removal. The loaded metallic oxides provided some alkaline groups to transport and store products to recover the active sites in the NO removal. C-O-C in ethers and C=O in quinones are main active sites for chemically absorbed SO2 while C-O in primary C-OH and C=O vibration in aliphatic groups are two sites for oxidizing NO. Competitive removal greatly improved the desulfurization capacity and slowed down the denitration process due to the occupation of active sites by SO2. Also, the generated sulfates leaded to the denitration deactivation while proper oxynitrides and nitrates promoted the absorption and oxidation of SO2.