A. Marcilla

Analysis of different kinetic models in the dynamic pyrolysis of cellulose

Abstract The kinetics of the thermal decomposition of cellulose in nitrogen were studied using dynamic TG at heating rates between 5 and 50 K min −1 . The most widely used models found in the literature which are usually applied in isothermal conditions were tested. Important differences were found between models that take into account the formation of an activated cellulose and those that assume the direct decomposition of cellulose to char, tar and gases. The best agreement between experimental and calculated values was found with models which consider the formation of activated cellulose and take into account the different behaviour at low and high temperatures. The simultaneous correlation of all the experimental data obtained in different conditions is proposed as a technique to prevent compensating effects between the pre-exponential factor and the activation energy, and thus to avoid erroneous conclusions.

Thermogravimetric studies on the thermal decomposition of polyethylene

Abstract The thermal decomposition of polyethylene was analyzed by dynamic and isothermal experiments. Dynamic runs with different heating rates, exposed surface and initial mass were carried out. Isothermal runs of different initial mass were also carried out. Several kinetic models were tested and the best fit to the experimental thermogravimetry curves was obtained with a model involving a surface zero-order reaction.

Thermogravimetric kinetic study of the pyrolysis of almond shells and almond shells impregnated with CoCl2

A kinetic study of the pyrolysis of almond shells, both with and without impregnation with CoCl2, has been carried out by thermogravimetric analysis (TGA). The experimental data have been discussed, assuming a scheme of two reactions as a simplification of the complex network of reactions. The corresponding kinetic parameters (apparent activation energy and pre-exponential factor), assuming first-order kinetics for both processes, have been calculated within the 200–410°C temperature range, for almond shells without impregnation, and between 150–420°C for almond shells impregnated with CoCl2. When pyrolysing almond shells without impregnation and assuming an overall reaction, the results agree with those obtained from other techniques (Analytical Equipment Pyroprobe 100 and Fluidized Bed Reactor pyrolysis) and also compare well with other results for pyrolysis of cellulose reported in the literature. In the pyrolysis of almond shells impregnated with CoCl2, the results obtained compare well with those from the Fluidized Bed Reactor and have been useful for explaining the differences between the kinetic data deduced from the Fluidized Bed Reactor and the Pyroprobe 100.

Comparative study of the pyrolysis of almond shells and their fractions, holocellulose and lignin. Product yields and kinetics

A comparison between the thermal decomposition of almond shells and their components (holocellulose and lignin) was carried out, considering the yields of the most important products, under flash conditions, and the decomposition kinetics. n nThe yields of the main gaseous products obtained in the fast pyrolysis of almond shells can be reproduced from the yields obtained with holocellulose and lignin. The best results were obtained with CO, water and CO2. The differences were greater with the minor hydrocarbons, CH4, C2H6, C2H4, etc. n nThe kinetics of the slow thermal decomposition (TG-DTG) of almond shells cannot be reproduced by the sum of lignin and holocellulose. The cellulose from almond shells decomposes at lower temperatures than almond shells, and the behavior of isolated lignin is very different from that found when it forms part of the raw material, proving the importance of the interactions between its components.

CO2 activation of olive stones carbonized under different experimental conditions

In order to get more detailed knowledge of the possible effect of the carbonization conditions on the pore structure of activated carbons three very different chars from a common precursor(olive stones) have been prepared under three different sets of experimental conditions

Pyrolysis of Kraft lignin: yields and correlations

Abstract A semibatch flow reactor connected in series between a Pyroprobe 1000 and a gas chromatographer was used to study the production of gases from Kraft lignin at different nominal temperatures (ranging from 500 to 900 °C) and different residence times of the volatiles in the hot zone. Using this experimental equipment, it is possible to differentiate between the primary reactions that take place in the Pyroprobe 1000 and the secondary reactions that take place in the secondary reactor. Yields of 13 pyrolysis products (methane, ethane, ethylene, propylene, propane, hydrocarbons with four carbon atoms, benzene, other aromatics, CO, CO 2 , methanol together with formaldehyde, acetaldehyde, acetic acid and water) were analyzed as a function of experimental conditions. Correlations of the products analyzed with those of methane are discussed.

Kinetic study of the thermogravimetric behavior of different rubbers

Abstract The thermal decomposition behavior of different rubbers has been studied. A kinetic model has been applied which allows a good correlation with the weight loss derivative data. It uses kinetic constants independent of the heating rate, and predicts the behavior of rubber mixtures, as well as the composition of the samples.

Influence of thermal treatment regime on the density and reactivity of activated carbons from almond shells

Abstract A study of the influence of two successive thermal treatments, at low (3–4°Cxa0min −1 ) and high (ca. 3000°Cxa0min −1 ) heating rate, on the properties and reactivity of chars obtained from almond shells was carried out. The combined thermal treatment consisted of a first stage at intermediate temperatures from 275 to 400°C at the low heating rate, followed by a second stage at the high rate, up to 850°C. All the samples obtained under these conditions (except the sample obtained at an intermediate temperature of 400°C) yielded a density much lower than that corresponding to a single thermal treatment up to 850°C at both heating rates. The sample obtained at 400°C behaved in a very interesting manner since its density was the highest obtained. A correlation has been obtained between the high reactivity of the samples obtained by a single treatment at high heating rate, and the Ca content and dispersion. The adsorption properties of the activated carbons obtained at approximately 50% burn-off were very similar regardless of the reactivity and the porous structure of the precursor chars.

Comparative study of the main characteristics and composition of the mainstream smoke of ten cigarette brands sold in Spain.

In this study 10 commercial top selling cigarette brands in Spain have been machine smoked and the mainstream smoke has been analyzed. Multifunctional analysis has been satisfactorily employed to correlate the effect of the main design features of the cigarettes including amount of tobacco, filter size or paper weight with the amount of smoked tobacco and with the ratio CO(2)/CO. The composition of the vapor phase and that of the particulate matter have been analyzed. The particulate matter retained in the filter of the cigarettes has also been analyzed showing a distinct behavior of the compounds condensed in the cigarette filters and in the traps, related to their retention time. A general trend for the relative yield of some compounds in the different brands have been identified and confirmed by multifunctional analysis. Nevertheless, there are some noticeable compounds that behave differently in the different brands.

Thermal treatment and foaming of chars obtained from almond shells : kinetic study

Abstract The influence of a combined thermal treatment on the density of chars obtained from almond shells has been investigated. The thermal treatment involves two steps at different heating rates: the first one up to temperatures of 225–400°C; and the second one up to 850°C. Thermogravimetric experiments have been carried out with the intermediate chars obtained after treatment revealing the evolution of the different fractions of the almond shells (i.e. hemicellulose, cellulose and lignin), and their influence on the final density of the chars. An intermediate treatment, where the gases evolved from the last remaining fractions of the cellulose coincide with the char in a fluid or soft state, is required to foam the particles. A kinetic model has been applied to quantify, with excellent results, the evolution of the different fractions.