Influence of the holding temperature of the first heating step in a two-heating step carbonisation process on the properties of chars and activated carbons from almond shells

Almond shells were carbonised and activated in a laboratory scale vertical reactor under different conditions to study the influence of the relative i ntensity of a first slow heating rate step and a second fast heating rate s tep on the activated carbon obtained. Results have proved that the higher t he intensity of the second heating step (i.e. the lower the final temperatu re of the first heating step), the lower the char yield and the higher the reactivity. The surface areas of the chars obtained do not explain the diff erences in reactivity observed, which could be explained by a detailed anal ysis of the inorganic compounds in the samples. At final temperatures of th e first heating step of 285-300 degreesC a decrease in the density of the c hars obtained was observed, resulting in chars with a highly foamed texture . The mechanical resistance of these samples was accordingly lower. The kno wledge of the influence of this two-heating stage process on the activated carbons obtained allows the selection of the adequate preparation condition s in order to obtain the desired properties. (C) 2001 Elsevier Science B.V. All rights reserved.