Preparation of Activated Carbons from Bituminous Coals with CO₂ Activation. 1. Effects of Oxygen Content in Raw Coals

Abstract

Activated carbons were prepared from three Australian bituminous coals in this study. The preparation process consisted of carbonization followed by activation in CO2. Experimental results reveal that the oxygen content of the coals has a great influence on the behavior during preparation and on the properties of the products. The coal with a higher O/C atomic ratio has a lower peak temperature for volatile evolution during carbonization and is able to produce a char with a higher surface area. The reactivity in CO2, the surface area, and the pore volume of the resulting activated carbon are all increasing functions of the O/C ratio of the coal precursors. An SEM study shows that at high burn-off levels a higher portion of gasification occurs at the exterior surface of the carbon from the coal with a lower O/C ratio, indicating that the diffusion resistance may be stronger for this carbon. For the same coal precursor, the average pore diameter of the activated carbon increases as the temperature for activation is increased in the range of 800−900 °C.