Chemical study of extracted rockrose and of chars and activated carbons prepared at different temperatures

This paper discusses the chemical composition and chemical structure of roc krose (Cistus ladaniferus L.) extracted into petroleum ether and resulting chars as well as activated carbons. The isothermal temperature of carboniza tion of extracted rockrose (Jex) in N-2 ranged between 600 and 1000 degrees C. The char (C-Jex-600) employed in the preparation of activated carbons w as prepared by treatment of Jex at 30-600 degrees C. This char was heated i n N-2 before activation, which was carried out in CO2 or steam at 700-950 d egrees C to 40% burn-off. Chemical analyses, Fourier transform infrared spe ctroscopy, thermogravimetry and X-ray diffraction techniques have been appl ied. The extraction does not exert a significant influence on the organic c hemical structure of raw material. In ash prepared at 600 degrees C from Je x (ash content 1.29%), the major elements are Ca, K, Mg and P; calcite is t he main component. When this ash is heated at 950 degrees C, lime is the ma in component. The chars and activated carbons contain carbon-carbon double bonds and ether structures; C-Jex-600 also contains carbonyl groups. The et her groups decrease with the temperature increase. The analyses of chars an d activated carbons show an ash content close to 6-8%, and calcite as the m ain component. The presence of whewellite, CaC2O4. H2O, indicates that the pyrolysis is delayed in the preparation of C-Jex-600, that a partial calciu m-carboxylate association occurs, and that hydration takes place during sto rage period. The mineral matter of the activated carbons prepared at 700 de grees C depends on the activating agent: calcite is the only component iden tified using CO,, whereas lime, portlandite and vaterite are also identifie d using steam. At higher temperatures, the mineral matter is practically in dependent of the activating agent. Probably, CaO transforms into Ca(OH)(2) and CaCO3 during the char and activated carbon storage periods. (C) 1999 El sevier Science B.V. All rights reserved.