Modification of the porous structure along the preparation of activated carbon monoliths with H3PO4 and ZnCl2

Two series of activated carbon monoliths (discs) have been prepared by chemical activation of olive stones with phosphoric acid or zinc chloride, without the use of any binder. A conforming step was introduced between impregnation with the chemical and heat treatment. Two equivalent series of granular activated carbons were also prepared in order to analyse the effect of conforming pressure on the porosity of the final activated carbon. The evolution of microporosity and the micropore size distribution has been followed by gas adsorption (N-2 at -196 degrees C and CO2 at 0 degrees C) and immersion calorimetry into three liquids with different molecular dimensions (dichloromethane, benzene and 2,2-dimethylbutane). The experimental results indicate that activation by both chemicals produces a large development of microporosity but the differences between the granular and monolithic forms are more noticeable when using phosphoric acid. Thus, there is mainly a reduction in the interparticle space and macroporosity during the formation of the discs prepared using zinc chloride whereas there is an additional reduction in the volume and dimension of the meso- and microporosity when using phosphoric acid. The different behaviour of the two chemicals has been related to their effect on the precursor along the impregnation step. (C) 2007 Elsevier Inc. All rights reserved.