Role of chemical activation in the development of carbon porosity

Lignocellulosic materials such as olive and peach stones have been used as precursors for granular activated carbon, using phosphoric acid, zinc chloride and potassium hydroxide as activating agents. Although the three chemicals produce a large development of microporosity, there are clear differences among them when increasing the degree of activation. Thus, whereas KOH only produces a widening of micropore width, ZnCl2 additionally develops small mesoporosity and H3PO4 leads to a more heterogeneous pore size distribution. These differences in the porosity development have been related to the different activation mechanism for each chemical. On the other hand, impregnation ratios of ZnCl2 and H3PO4 leading to high volume of micropores of homogeneous width have been selected to prepare binderless carbon monolithic discs able to adsorb large amounts of methane at 3.4 MPa, on which the experimental density of adsorbed methane has been determined. (C) 2004 Elsevier B.V. All rights reserved.