J. Pastor-Villegas

FT-IR STUDY OF ROCKROSE AND OF CHAR AND ACTIVATED CARBON

Fourier transform-infrared spectroscopy was used in the study of rockrose (Cistus ladaniferus, L.) and of rockrose chars and activated carbons. Chars were prepared by heating the starting material between 200 and 1000 °C in nitrogen. Also, a sample was obtained at 600 °C in the atmosphere of the products of the thermal decomposition of rockrose. This charred product was used in the preparation of activated carbons. It was heated at 800 °C in air, CO2 or steam to 40% burn-off. The presence of oxygen groups and of olefinic and aromatic structures was detected in rockrose. The heat treatment of rockrose in the range 300–500 °C produced the most significant changes in the chemical structure of the material. Olefinic CC bonds and ether structures increased first in the chars and then the aromatic structure developed. Above 500 °C, the oxygen groups decreased with the temperature increase. The charring method of rockrose also influenced markedly the chemical structure of the chars. The use of a greater mass of sample slowed down the pyrolysis of rockrose. The activated carbons possessed aromatic CC bonds and oxygen groups.

Formation of oxygen structures by air activation. A study by FT-IR spectroscopy

Abstract Using cherry stones (CS) as starting material and commonly air as activating agent, formation of oxygen structures in activated carbon is investigated. In the preparation of samples, CS was first heated at temperatures between 450 and 900°C in N2 atmosphere. Then, in a successive activation stage, the product carbonized at 600°C was maintained in contact with an air stream at 25–325°C for 24 h, 300–600°C for 1 h, and 250°C for 1–96 h. The rest of the carbonization products of CS were also heated at 250°C in air for 24 h. Moreover, the product carbonized at 900°C was activated at 750 or 900°C in CO2 for 1 h. Furthermore, in a second activation stage, the products activated at such temperatures in CO2 and those at 300–600°C in air were heated at 250°C in air for 24 h. The starting material, carbonized products, and activated carbons were examined by FT-IR spectroscopy. A number of carbon–hydrogen atomic groupings and of oxygen groups and structures, i.e., OH, CO, and C–O–C) have been identified in CS. The yield of the activation and carbonization processes and also the chemical structure of the resultant products are strongly dependent on the carbonization temperature. In the products carbonized at 600–900°C, only ether type structures are detected. The activation at 250°C in air results in activated carbons that contain different oxygen structures when CS is carbonized at 450 or 600°C. At 750 or 900, by contrast, oxygen structures are not formed as a result of the activation treatment. This also applies when the carbonization product of CS at 900°C is activated solely in CO2 or first in CO2 and then in air. The heating conditions in air greatly influence the formation of oxygen structures (specifically, of lactonic and ion-radical types) to a large extent. It only occurs when activating at relatively low temperatures for a long time; at 300–600°C for 1 h, however, the oxygen structures are not formed.

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

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 dioxide/nitrogen) at 700–950°C to 40% burn-off. The techniques applied to study the pore structure were: pycnometry (mercury, helium), adsorption (carbon dioxide, 298 K; nitrogen, 77 K), mercury porosimetry and scanning electron microscopy. The preparation by steam activation, especially at 700°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°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 lowest activation temperatures, especially at 700°C, steam develops the mesoporosity much more than carbon dioxide. At 950°C, a similar reduction of pore volume in the macropore range occurs.

Characterization study of char and activated carbon prepared from raw and extracted rockrose

Abstract Using raw rockrose ( Cistus Ladaniferus, L. ) and rockrose extracted into petroleum ether, the effect of extraction on the thermal behaviour and chemical-physical properties of chars and activated products was studied. Chars were prepared by heat treatment of the starting materials under dynamic and isothermal conditions over the temperature range 200–1000°C. Activations of two carbonized products, which were obtained at 600°C, was accomplished in air, CO 2 , or steam at 850°C until burnoff 40%. Techniques used were thermogravimetry, gas adsorption, mercury porosimetry, density measurements and FT-IR spectroscopy. Extraction delayed the rockrose pyrolysis, as inferred from the thermal behaviour of the starting materials and by the composition and texture of the chars prepared between 200–600°C. At higher temperatures, extraction reduced the ash content of chars and mitigated the loss produced in the surface area and the microporosity. Differences in textural properties of activated carbon depended on the starting material and the activating agent, being especially significant between air and CO 2 or steam. The FT-IR spectra of the carbonized and activated products displayed absorption bands compatible with the presence in the materials of surface olefinic CC double bonds, aromatic rings, and oxygen functional groups.

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

The surface chemistry and the porous texture of activated carbons prepared from a charred product (Cjex-600), which was obtained from rockrose (Cistus ladaniferus, L.) extracted previously into petroleum ether, were studied. Activated carbons were prepared by heating Cjex-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 (N2, 77 K; CO2, 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 Cjex-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 Cjex-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 CO2 and steam under the same experimental conditions.

Organic chemical structure and structural shrinkage of chars prepared from rockrose

Abstract Chars were prepared by heating rockrose ( Cistus ladaniferus L) under dynamic and isothermal conditions between 200 and 1000°C in nitrogen. Several techniques including chemical analysis, Fourier transform infrared (FTIR) spectroscopy, molecular simulation, density measurements, mercury porosimetry and adsorption were used to study the chemical structure and pore structure. The chars prepared at high temperatures in particular contain oxygen in ether type structures, which may cross-link aromatic sheets. The degree of development of porosity in the chars and the porosity distribution seem to depend on the amount of volatile matter removed at each temperature during pyrolysis and on the structural shrinkage of the residual carbon. Both factors act contrarily on the pore structure of the chars, the latter effect being stronger at high temperatures. The shrinkage of the carbon structure may be caused by break down of interlayer carbon–oxygen bonds.

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

Abstract 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°C. The char (C Jex -600) employed in the preparation of activated carbons was prepared by treatment of Jex at 30–600°C. This char was heated in N 2 before activation, which was carried out in CO 2 or steam at 700–950°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°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°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, CaC 2 O 4 ·H 2 O, 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°C depends on the activating agent: calcite is the only component identified using CO 2 , 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 CaCO 3 during the char and activated carbon storage periods.

Pore structure of chars and activated carbons prepared using carbon dioxide at different temperatures from extracted rockrose

Abstract This paper discusses the pore structure of chars and activated carbons prepared at different temperatures from rockrose ( Cistus ladaniferus L.), extracted previously into petroleum ether. The isothermal temperature of carbonization in nitrogen ranged from 600 to 1000°C. The starting char for activated carbons was prepared by treating a larger amount of precursor in the atmosphere formed as temperature increased from 30–600°C, at 10°C min −1 , being the total heating time 120 min. This char was heated in nitrogen before activation, which was carried out using carbon dioxide at 700–950°C to 40% burn-off. Pycnometry (Hg, He), adsorption (N 2 , 77 K), mercury porosimetry and scanning electron microscopy techniques have been applied to the characterization. In the chars prepared in nitrogen, a shrinkage of the carbon structure is responsible for the pore narrowing in all the pore ranges, including a micropore closing above 800°C, which is attributed to the disappearance of ether groups. This shrinkage is less important in comparison with that occuring in chars prepared from rockrose without extraction. The starting char of the activated carbons presents a rudimentary pore structure due to the different conditions of its preparation. In the activated carbons, the pore volumes (micro, meso and macro) increase up to 750°C. At higher temperatures, the mesopore volume increases, whereas the micro- and macropore volumes decrease. These structural changes are discussed considering the starting char as a Ca-supported catalyst. A shrinkage of the carbon structure also occurs at high temperatures, without causing micropore closing.

Characterization of rockrose wood, char and activated carbon

Abstract The starting rockrose ( Cistus ladaniferus L.), as well as charred and activated products prepared by heat treatment conducted under different conditions, were characterized in terms of composition, calorific value, texture and surface chemistry. Techniques used were thermogravimetric analysis, gas adsorption, mercury porosimetry, density measurements, scanning electron microscopy and FT-IR. The rockrose composition and calorific value were similar to other woods. Rockrose chars were prepared by heat treatment of the material over the temperature range 200–1000°C. The production of charcoal occurred at 400°C. Above 600dgC the microporous structure of the chars became partially closed. Activated carbons were prepared by gasification (burnoff = 40%) of a carbonized product (carbonization temperature = 600°C) in air at 600°C and in CO 2 and steam at 750°C. Significant differences in properties of the activated carbons were noted depending on the activating agent. Activated carbon produced in steam possessed better textural characteristics, in particular the development of mesoporosity was observed. The presence of surface oxygen groups containing CO bonds, which may be formed from C=C bonds, was greater with air and steam than with CO 2 .

Riesgos Debido a la Radiactividad Natural de Pizarras de Construcción

The aim of this work is to measure the natural radioactivity in slates used as building material. Slates manufactured in the region of Extremadura-Spain were used as a study case. The concentrations were determined by gamma spectrometry using an HPGe coaxial detector. Radium equivalent activities (Raeq) and various hazard indices were also calculated. Results were also compared with the data available in the literature for other countries of the world. The results show that the average values of the concentrations due to 40 K, 226 Ra and 232 Th were found 840, 29 and 75 Bq/kg, respectively. The radium equivalent activity was less than the accepted standard criterion value of 370 Bq/kg and the values of other hazard indices were also below their limit values.