Heat treatment of rockrose char in air. Effect on surface chemistry and porous texture

Abstract

The surface chemistry and the porous texture of activated carbons prepared from a charred product (C jex-600), which was obtained from rockrose ( Cistus ladaniferus, L.) extracted previously into petroleum ether, were studied. Activated carbons were prepared by heating C jex-600 between 350 and 850 °C in air to 40% burnoff. Methods of chemical analysis and FTIR spectroscopy as well as techniques of gas adsorption (N 2, 77 K; CO 2, 298 K), mercury porosimetry, and density measurements were applied. In the FTIR study of the samples, the presence of surface olefinic CC double bonds, aromatic rings, and oxygen functional groups was detected. Carbonyl groups were only found to a significant extent in C jex-600 and in the activated carbon prepared at 350 °C. The microporosity developed with increasing temperature between 350 and 750 °C. At higher temperatures, pore narrowings occurred. The gasifying action of air was strongly dependent on the removal of nonorganized matter from C jex-600 and on the pore size. The reaction time needed at 850 °C in air to reach burnoff 40% was less than a half of that at 350 °C, and was comparable to the times required in CO 2 and steam under the same experimental conditions.