Textural characterization of active carbons using fractal analysis

Abstract

This study continues a previous work aiming to explore how fractal analysis may help to understand the textural changes of materials during the manufacture of active carbons. Textural characterization of active carbons is carried out in order to obtain a better understanding of the facts underlying char gasification. The materials selected for study were a series of active carbons obtained from chars by means of gasification with carbon dioxide at 1123 K. These chars were obtained from coals oxidized in air at various temperatures for different periods of time. The data from mercury porosimetry were analyzed using fractal models. The fractal dimensions for the active carbons were calculated by using the methods proposed by Friesen and Mikula, by Zhang and Li and the method of Neimark. This latter method was used to obtain fractal profiles of the chars that were compared with the corresponding fractal profiles of the precursor chars and coals. Pore development during activation depends – together with other factors that remain constant in this study – on the textural properties of the precursor char that, at the same time, are conditioned by the properties of coals. The evolution of the fractal characteristics of the active carbons is also studied. At the same time, a detailed study of pore volume development during activation is presented. These analyses help to clarify the role that various phenomena occurring during activation have on the textural properties of the active carbons.