Pore structure of activated carbons prepared by carbon dioxide and steam activation at different temperatures from extracted rockrose

摘要

The influence of the activation temperature on the pore structure of granular activated carbons prepared from rockrose (Cistus ladaniferus L.), extracted previously into petroleum ether, is comparatively studied. The preparation was carried out by pyrolysis of a char in nitrogen and its subsequent activation by carbon dioxide and steam (flow of water controlled to generate the same mol number per minute of water as well as carbon dioxideitrogen) at 700-950 deg C to 40% burn-off. The techniques applied to study the pore structure ewre: pyrcnometry (mercury, helium), adsorption (carbon dioxide, 298 K; nitrogen, 77 K), mercury porosimetry and scanning electron microscopy. The preparation by steam activation, especially at 700 deg C, yields activated carbons showing a total pore volume larger than those prepared by carbon dioxide activation. The pore structures present the greatest differences when the activations are carried out between 700 and 850 deg C and closer at higher temperatures. At high temperatures, the decrease of differences in pore development caused by carbon dioxide or steam is attributed to an external burn-off. The micropore structure of each activated carbon is mainly formed by wide micropores. At the lwoest activation tempertures, especially at 700 deg C, steam develops the mesoporosity much more than carbon dioxide. At 950 deg C, a similar reduction of pore volume in the macropore range occurs.