Surface characterization and SO2 removal activity of activated semi-coke with heat treatment

The activity of SO2 removal by activated semi-coke is influenced by the precursor and surface modification processes. Raw semi-coke was modified by heat treatment at 800 °C in a nitrogen flow, and its activity for SO2 removal was tested in a fixed bed reactor. The surface chemical properties of both raw semi-coke and activated semi-coke were characterized by acid-base titration, XPS, and FTIR. Graphitic carbon was the major component of carbon functional groups in the surface of both raw semi-coke and activated semi-coke. Surface C=O groups in the forms of ketone, lactone, carbonyl, or quinone were the main surface oxygen functional groups, and pyrrolic and/or pyridon-N groups were the main nitrogen functional groups in raw semi-coke. The heat treatment resulted in the decomposition of surface oxygen functional groups and the redistribution of surface oxygen and nitrogen functional groups. The content of the surface carbon groups, such as C=O decreased dramatically after heat treatment. However, the content of surface oxygen functional groups, such as ethers and chemisorbed oxygen or water increased on the surface of activated semi-coke. The number of pyridine-like structures was increased by the removal of pyrrolic and/or pyridon-N groups in the activation process. The increase of ethers group and π-π* transitions in aromatic systems, and the change of the nitrogen functional groups increased the surface basicity for activated semi-coke. Activated semi-coke had the higher activity for SO2 removal than did raw semi-coke. The surface features influencing the activity for SO2 removal for activated semi-coke may be ethers, aromatic carbons and nitrogen functional groups with basicity.