The use of steam and CO2 as activating agents in the preparation of activated carbons

Four series of activated carbon have been prepared from carbonized olive stones. One of them, series D, was prepared using carbon dioxide as activating agent, and the other three, series AV, W, and H, with water vapor under different experimental conditions. Two of the series, D and H, were prepared in such a way that the gasification rate for both reactants was identical, in an attempt to reduce the effect of the relative differences in diffusion and accessibility of both gases to the interior of the particles. The changes in porosity of the original char during activation have been studied by adsorption of N2 at 77 K and CO2 at 273 K, as well as by mercury porosimetry. The results obtained show that carbon dioxide produces an opening, followed by widening, of narrow microporosity, whereas water vapor widens the microporosity from the early stages of the process, the resulting activated carbon exhibiting lower micropore volume. However, dilution of water vapor and high activation temperatures approach the development of total microporosity by steam to that of carbon dioxide, although there is a more important role of narrow microporosity widening in the former.