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 intensity of a first slow heating rate step and a second fast heating rate step on the activated carbon obtained. Results have proved that the higher the intensity of the second heating step (i.e. the lower the final temperature 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 differences in reactivity observed, which could be explained by a detailed analysis of the inorganic compounds in the samples. At final temperatures of the first heating step of 285-300 degreesC a decrease in the density of the chars obtained was observed, resulting in chars with a highly foamed texture. The mechanical resistance of these samples was accordingly lower. The knowledge of the influence of this two-heating stage process on the activated carbons obtained allows the selection of the adequate preparation conditions in order to obtain the desired properties. (C) 2001 Elsevier Science B.V. All rights reserved.