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 SBET/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 SBET (1274.64 m2 g-1) at a low burn-off value (22.5%) has the highest SBET/burn-off ratio value of 56.65 m2 g-1/%, whereas the JX-800 char with a low value of SBET (564.19 m2 g-1) at a burn-off value of 58.2% has the lowest SBET/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 SBET/burn-off.