Improvement of Activated Carbon from Jixi Bituminous Coal by Air Preoxidation

Air preoxidation has been demonstrated as a good method to change the structure of Jixi bituminous char for controlling development of porosity at low burnoff under physical activation. In this work, the influences of different oxidation times in air at 200 °C (0, 3, 15, 48, and 96 h) were studied. The removal of aliphatic chains and the increase of the type and quantity of oxygen functional groups occur at the preoxidation stage, resulting in an open structure for oxidized coals; however, slight improvement is made on the porosity and surface morphology. In the pyrolysis stage, the evolution of different oxygen-containing structures plays a more important role than the loss of plastic behavior on disordered conversion of oxidized chars, leading to production of more active sites and development of the meso- and macropores. In the activation stage, serious carbon losses at the surfaces of particles is observed in JX-800-59.1 with the low values of SBET (589.41 m2/g) because of the unfavorable diffusion of activated gas. Alternatively, the well-developed pore structure of JXO15-800 and JXO48-800 chars promotes the favorable diffusion of activated gas, thereby hindering the severe carbon losses at the particle surface, but JXO48-800 char with more disordered structure and active sites has a high value of SBET (818.98 m2/g) at a low value of burnoff of 30.5% compared to the values of SBET (705.69 m2/g) of JXO15-800 char at a value of burnoff of 42.6%.