Effects of oxygen functional groups and FeCl3 on the evolution of physico-chemical structure in activated carbon obtained from Jixi bituminous coal

Abstract

It is crucial to increase the values of S_BET/burn-off ratio to achieve activated carbon (AC) with a higher SO₂ adsorption capacity at a low cost from flue gas. In this study, at first, Jixi bituminous coal was used as a raw material to prepare a series of pre-treated samples by oxidation treatment and adding different amounts of the FeCl₃ catalyst. Then, the AC samples were prepared by pyrolysis under a N₂ atmosphere and physical activation with CO₂. Finally, the change in the physico-chemical structure of different samples was determined to study the effects of oxygen functional groups and FeCl₃. The results show that the rapid growth of mesopores is mainly influenced by the evolution of oxygen functional groups, whereas the micropores are mainly influenced by the FeCl₃ catalyst during pyrolysis. These effects can also further improve the size and the carbon type of the aromatic structure from a different perspective to promote the disordered microstructure of treated chars (1FeJXO15-800H, 3FeJXO15-800H and 6FeJXO15-800H) as compared to the ordered microstructure and less pores of the un-pretreated char (JX-800). Then, the active sites can no longer be consumed preferentially in the presence of the catalyst; this results in the continuous disordered conversion of the microstructure as compared to the ordered conversion of JX-800 char during activation. On the one hand, the developed initial pores of 1FeJXO15-800H, 3FeJXO15-800H, and 6FeJXO15-800H chars promote the favorable diffusion of activated gas, following the non-hierarchical development. On the other hand, the presence of Fe-based catalysts facilitates the etching of carbon structure and the rapid and continuous development of the micropores, hindering the severe carbon losses on the particle surface. Finally, the 3FeJXO15-800H char with a high value of S_BET (1274.64 m² g⁻¹) at a low burn-off value (22.5%) has the highest S_BET/burn-off ratio value of 56.65 m² g⁻¹/%, whereas the JX-800 char with a low value of S_BET (564.19 m² g⁻¹) at a burn-off value of 58.2% has the lowest S_BET/burn-off ratio value of 9.69 m² g⁻¹/%. Therefore, the presence of oxygen functional groups and FeCl₃ has obviously changed the evolution of the physico-chemical structure in activated carbon to effectively enhance the values of S_BET/burn-off.