Adsorption properties and porous structure within granules of activated carbons with different burn-off

Two activated carbons of AG type obtained by activation with the steam of carbonised granules prepared from hard coal and tar were examined. One of them has a lower (41%) and the other a higher (54%) level of burn-off. The quantitative evaluation of radial differentiation of porous structure has been made on the basis of analysis of samples obtained by gradual removal of the outer layer of activated carbon granules using the attrition process in the spouted bed. The abrasion treatment was carried out in two steps: elimination of about 33 and 66% of the total granule weight. The benzene vapour adsorption–desorption isotherms and ash contents were determined for all samples obtained from both source carbons. The evaluation of micropore structure parameters on the basis of benzene vapour adsorption isotherms was done using the adsorption equations proposed by Dubinin–Radushkevich, Dubinin–Stoeckli and Horvath–Kawazoe. The fractal analysis and changes of surface roughness as a function of granule radius was performed for all samples. The comparison of the porous structure and fractal dimensions of corresponding samples of activated carbons with different levels of activation was done.