The pyrolysis of particles of glucomannan, the main component of softwood hemicelluloses, is investigated in a fluidized-bed reactor. A first set of experiments is carried out for temperatures in the range 530–690 K to determine yields and composition of products. The most abundant are char, water, and carbon dioxide. The condensable organic fraction mainly consists of acetic acid, formic acid, hydroxypropanone, hydroxyacetaldehyde, and furfuryl alcohol. The second set of experiments is made to determine the weight loss characteristics of small samples exposed in the expanded bed at temperatures of 503–593 K that are then used to develop one- or two-stage pyrolysis mechanisms.
Pyrolysis kinetics of a hardwood representative, beech (Fagus sylvatica), was investigated by two different kinetic approaches: model-free isoconversional method and model-fitting method. The model-free isoconversional method was used for the determination of apparent kinetic parameters, i.e. the activation energy and pre-exponential factor. The model fitting method was used for the optimization of kinetic parameters of the reaction pathways of three selected reaction mechanisms: one-step, two-step, and three-step one. In both approaches, thermo-gravimetric data were used at five heating rates: 2°C min−1, 5°C min−1, 10°C min−1, 15°C min−1 and 20°C min−1. As the most suitable mechanism, the three-step mechanism containing the intermediate degradation step was chosen. This selection was supported by experimental results from the 13C NMR analysis of solid residues prepared at the key temperatures within the range of 230–500°C. The progress of mass fraction values of each component in this mechanism was simulated. Conclusions from the simulation were confronted with experimental results from the 13C NMR.
Activated sewage sludge samples obtained from two different waste water treatment plants were investigated by thermogravimetric analysis. Due to a very high content of water in the sludge samples, these had to be dried at 160°C in an electrical oven in order to remove all adsorbed water. To ensure pyrolysis conditions, nitrogen atmosphere was applied. The pyrolysis decomposition process was carried out in the temperature range from ambient temperature to 900°C at three different heating rates: 2 K min−1, 5 K min−1, 10 K min−1. TGA and DTG curves of the decomposition processes were obtained. Temperature of onset decomposition, final temperature of decomposition, maximum decomposition rate, and decomposition temperature were determined by thermogravimetric analysis for both sludge samples used. The main decomposition process takes place at temperatures in the range from 230°C to 500°C. Above this temperature, there are only small changes in the mass loss which are often attributed to the decomposition of carbonates present in the sewage sludge samples. To determine the apparent kinetic parameters such as the activation energy and the preexponential factor, the so called Friedman isoconversional method was used. Because of the requirements of this method, initial and final parts of the decomposition process, where crossings of the decomposition lines occurred, were cut off. Obtained dependencies of the apparent activation energies and preexponential factors as a function of conversion were used backwards to calculate the modeled decomposition process of sewage sludge and the experimental data were in good accordance with the data obtained by simulation.
Pyrolysis of a hardwood representative, beech sawdust (Fagus sylvatica), was investigated by thermogravimetry, a thermal analysis technique. A suitable kinetic approach for the determination of kinetic parameters was proposed. The model fitting method was used to optimize the kinetic parameters of the reaction pathways of the selected reaction mechanisms. The experiments were conducted starting from ambient temperature up to 600 °C using the following five heating rates: 2, 5, 10, 15, and 20 °C min -1 . FTIR, Py-GC/MS, 13 C NMR, and elemental analysis were also used to analyse the pyrolysis products. Differentiation among the reaction mechanisms of lignocellulosic material pyrolysis was performed. The three-step parallel mechanism containing an intermediate was the most suitable mechanism based on 13 C NMR analysis of solid residues prepared at the selected temperatures from 230-500 °C. The NMR results showed that the inclusion of an intermediate into the reaction scheme was a reasonable step. It was concluded that the intermediate was connected with the lignin structure.
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