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 rockrose (Cistus ladaniferus L.) extracted into petroleum ether and resulting chars as well as activated carbons. The isothermal temperature of carbonization 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 was prepared by treatment of Jex at 30-600 degrees C. This char was heated in N-2 before activation, which was carried out in CO2 or steam at 700-950 degrees C to 40% burn-off. Chemical analyses, Fourier transform infrared spectroscopy, thermogravimetry and X-ray diffraction techniques have been applied. The extraction does not exert a significant influence on the organic chemical structure of raw material. In ash prepared at 600 degrees C from Jex (ash content 1.29%), the major elements are Ca, K, Mg and P; calcite is the main component. When this ash is heated at 950 degrees C, lime is the main component. The chars and activated carbons contain carbon-carbon double bonds and ether structures; C-Jex-600 also contains carbonyl groups. The ether groups decrease with the temperature increase. The analyses of chars and activated carbons show an ash content close to 6-8%, and calcite as the main component. The presence of whewellite, CaC2O4. H2O, indicates that the pyrolysis is delayed in the preparation of C-Jex-600, that a partial calcium-carboxylate association occurs, and that hydration takes place during storage period. The mineral matter of the activated carbons prepared at 700 degrees C depends on the activating agent: calcite is the only component identified using CO,, whereas lime, portlandite and vaterite are also identified using steam. At higher temperatures, the mineral matter is practically independent of the activating agent. Probably, CaO transforms into Ca(OH)(2) and CaCO3 during the char and activated carbon storage periods. (C) 1999 Elsevier Science B.V. All rights reserved.