Kinetic study of pyrolysis of waste water treatment plant sludge

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.     

Pyrolytic characteristics and kinetics of pistachio shell by thermogravimetric analysis

Pyrolytic characteristics and kinetics of pistachio shell were studied using a thermogravimetric analyzer in 50?C800?°C temperature range under nitrogen atmosphere at 2, 10, and 15?°C?min^?1 heating rates. Pyrolysis process was accomplished at four distinct stages which can mainly be attributed to removal of water, decomposition of hemicellulose, decomposition of cellulose, and decomposition of lignin, respectively. The activation energies, pre-exponential factors, and reaction orders of active pyrolysis stages were calculated by Arrhenius, Coats?CRedfern, and Horowitz?CMetzger model-fitting methods, while activation energies were additionaly determined by Flynn?CWall?COzawa model-free method. Average activation energies of the second and third stages calculated from model-fitting methods were in the range of 121?C187 and 320?C353?kJ?mol^?1, respectively. The FWO method yielded a compatible result (153?kJ?mol^?1) for the second stage but a lower result (187?kJ?mol^?1) for the third stage. The existence of kinetic compensation effect was evident.     

Devolatilization behaviour and pyrolysis kinetic modelling of Spanish biomass fuels

The basic pyrolysis behaviour of eight different biomass fuels has been tested in a thermogravimetric analyser under dynamic conditions (5, 20 and 50 °C min^?1 heating rates) from room temperature up to 1,000 °C. Their decomposition was successfully modelled by three first-order independent parallel reactions, describing the degradation of hemicellulose, cellulose and lignin. Hemicellulose would be the easiest one to pyrolyse, while lignin would be the most difficult one. Experimental and calculated results show good agreement. The reactivity of the different biomass type functions of various thermal, kinetic and composition parameters are discussed. The effect of the heating rate on pyrolysis behaviour was studied, and a comparison between slow and fast heating rate reveals a small displacement of the DTG profiles to higher temperatures. The heating rate not only affects the highest mass loss rate temperature but also influences the mass loss rate value.     

Decomposition of Bio-polymers of Some Mediterranean Plants During Heating

Forest fires are a plague for all countries in the world. Many factors can induce them. The organic matter (‘fuel’) in the plant, is often responsible for the start of the fire. The bio-polymers and mainly the cellulose decompose at about 300°C with flammable evolved gas. This decomposition is first order, and the activation energy is about 180 kJ mol⁻¹ . On the other hand, the degradation of the lignin seems more complex, but we observed on many samples, a linearly decomposition of the lignin vs. the heating rate (in the interval close to the start of the forest fire, 300 to 3000°C h⁻¹ ). The decomposition of the plant during the heat is mainly dependent on the cellulose level. This degradation is also slightly dependent on the lignin level mainly if the lignin present in this plant is less stable. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermogravimetric analysis of walnut shell as pyrolysis feedstock

Thermal degradation behavior and kinetics of a biomass waste material, namely walnut shell, were investigated by using a thermogravimetric analyzer. The desired final temperature of 800 °C was achieved at three different heating rates (2, 10, and 15 °C min^?1) under nitrogen flow (50 mL min^?1). The TG and DTG curves exhibited three distinct zones that can mainly be attributed to removal of water, decomposition of hemicellulose + cellulose, and decomposition of lignin, respectively. The kinetic parameters (activation energy, pre-exponential factor, and reaction order) of active pyrolysis zone were determined by applying Arrhenius, Coats?CRedfern, and Horowitz?CMetzger methods to TG results. The values of activation energies were found to be between 45.6 and 78.4 kJ mol^?1. There was a great agreement between the results of Arrhenius and Coats?CRedfern methods while Horowitz?CMetzger method yielded relatively higher results. The existence of kinetic compensation effect was evident.     

Thermal behaviour of cephalexin in different mixtures

The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate, starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min⁻¹. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min⁻¹. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears. These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates: 5, 7, 10 and 12 °C min⁻¹. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion dependence on the reaction rate and less speculative discussions on the kinetic model. All there methods had furnished very near values of the activation energy, this being an argument for a single thermooxidative degradation at the beginning (192–200 °C).     

Investigation of thermal behavior of nicotinic acid

The thermal behavior of nicotinic acid under inert conditions was investigated by TG, FTIR and TG/DSC-FTIR. The results of TG/DSC-FTIR and FTIR indicated that the thermal behavior of nicotinic acid can be divided into four stages: a solid-solid phase transition (176–198°C), the process of sublimation (198–232°C), melting (232–263°C) and evaporation (263–325°C) when experiment was performed at the heating rate of 20 K min⁻¹. The thermal analysis kinetic calculation of the second stage (sublimation) and the fourth stage (evaporation) were carried out respectively. Heating rates of 1, 1.5, 2 and 3 K min⁻¹ were used to determine the sublimation kinetics. The apparent activation energy, pre-exponential factor and the most probable model function were obtained by using the master plots method. The results indicated that sublimation process can be described by one-dimensional phase boundary reaction, g(α)=α. And the ‘kinetic triplet’ of evaporation process was also given at higher heating rates of 15, 20, 25, 30 and 35 K min⁻¹. Evaporation process can be described by model of nucleation and nucleus growing, .     

Thermal decomposition of methylxanthines

The thermal decomposition of theophylline, theobromine, caffeine, diprophylline and aminophylline were evaluated by calorimetrical, thermoanalytical and computational methods. Calorimetrical studies have been performed with aid of a heat flux Mettler Toledo DSC system. 10 mg samples were encapsulated in a 40 μL flat-bottomed aluminium pans. Measurements in the temperature range form 20 to 400°C were carried out at a heating rate of 10 and 20°C min⁻¹ under an air stream. It has been established that the values of melting points, heat of transitions and enthalpy for methylxanthines under study varied with the increasing of heating rate. Thermoanalytical studies have been followed by using of a derivatograph. 50, 100 and 200 mg samples of the studied compounds were heated in a static air atmosphere at a heating rate of 3, 5, 10 and 15°C min⁻¹ up to the final temperature of 800°C. By DTA, TG and DTG methods the influence of heating rate and sample size on thermal destruction of the studied methylxanthines has been determined. For chemometric evaluation of thermoanalytical results the principal component analysis (PCA) was applied. This method revealed that first of all the heating rate influences on the results of thermal decomposition. The most advantageous results can be obtained taking into account sample masses and heating rates located in the central part of the two-dimensional PCA graph. As a result, similar data could be obtained for 100 mg samples heated at 10°C·min⁻¹ and for 200 mg samples heated at 5°C min⁻¹.     

Kinetic Aspect of Thermal Decomposition of Natural Phosphate and its Kerogen. Influence of heating rate and mineral matter

The natural phosphate and its demineralization products from Moroccan deposit were pyrolysed in a thermogravimetric analyser (TG) to examine the influence of the heating rate and mineral matter on their thermal decomposition. The heating rates investigated in the TG were 5–100°C min⁻¹ to final temperature of 1200°C. The integral method was used in the analysis of the TG to determine the kinetic parameters. It has been found that for the natural phosphate and corresponding kerogen analysed in the TG, the increase of the heating rate shifts the maximum rate loss to higher temperature. A first order reaction was found to be adequate for pyrolysis in the range 150–600°C which was attributed to kerogen decomposition. In addition, the results indicate that the removal of mineral matter affected the kinetic parameters found for kerogen in the natural phosphate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Research of thermal decomposition kinetic characteristic of emulsion explosive base containing Fe and Mn elements

The kinetic characteristic of thermal decomposition of the Emulsion Explosive Base Containing Fe and Mn elements (EEBCFM) which was used to prepare nano-MnFe₂O₄ particles via detonation method was investigated by means of non-isothermal DSC and TG methods at various heating rates of 2.5, 5 and 7.5°C min⁻¹respectively under the atmosphere of dynamic air from room temperature to 400°C. The results indicated that the EEBCFM was sensitive to temperature, especially to heating rate and could decompose at the temperature up to 60°C. The maximum speed of decomposition (dα/dT)_m at the heating rate of 5 and 7.5°C min⁻¹ was more than 10 times of that at 2.5°C min⁻¹ and nearly 10 times of that of the second-category coal mine permitted commercial emulsion explosive (SCPCEE). The plenty of metal ions could seriously reduce the thermal stability of emulsion explosive, and the decomposition reaction in the conversion degree range of 0.0∼0.6 was most probably controlled by nucleation and growth mechanism and the mechanism function could be described with Avrami-Erofeev equation with n=2. When the fractional extent of reaction α>0.6, the combustion of oil phase primarily controlled the decomposition reaction.     

Thermal analysis of sulfurization of polyacrylonitrile with elemental sulfur

Thermal analysis of sulfurization of polyacrylonitrile (PAN) with elemental sulfur was investigated by thermogravimetry and differential thermal analysis of the mixture of polyacrylonitrile and elemental sulfur up to 600°C. Due to the volatilization of sulfur, the different heating rate (10 and 20 K min⁻¹) and different mixture proportion of polyacrylonitrile and elemental sulfur were adopted to run the analysis. The different heating rates make the DSC curves of sulfur different, but make the DSC curves of PAN similar. In the DSC curve of sulfur for the heating rate of 20 K min⁻¹ around 400°C, a small exothermic peak occurs at 400°C in the wide endothermic peak around 380∼420°C, indicative of that there is an exothermic reaction around 400°C. In the DSC curves of the mixture, the peaks around 320°C are exothermic as the content of sulfur is below 3.5:1 and endothermic as the content of sulfur is over 4:1, indicating that one of the reactions between PAN and sulfur takes place around 320°C. In the TG curves of the mixture, the mass losses begin at 220°C, and sharply drop down from 280°C. The curves for the low sulfur content obviously show two steps of mass loss, and curves for the high sulfur content show only one step of mass loss, indicative of more sulfur is benefit for the complete sulfurization of PAN. This study demonstrates that the TG/DSC analysis can give the parameter for the sulfurization, even if the starting mixture contains the volatile sulfur.     

A kinetic study on the thermal behaviour of chitosan

The thermal behaviour of chitosan was studied by means of thermogravimetry, mass spectrometry and infrared spectrometry. Kinetic parameters were obtained by advanced kinetic evaluation (differential isoconversional analysis) from DSC curves, in non-isothermal conditions, at several heating rates, between 5 and 30°C min⁻¹. The results showed that the decomposition of chitosan does not follow a single mechanism because both the activation energy and the pre-exponential factor are not constant during the course of the reaction. A comparison with the results obtained by applying different conventional calculating methods is also shown.     

Characterization of low molecular weight organic acids from beech wood treated in supercritical water

Japanese beech (Fagus crenata Blume), its cell wall components, and model compounds were treated by supercritical water (380°C, 100 MPa) for 5 s using a batch-type reactor to investigate the production behavior of low molecular weight organic acids. It was found that cellulose and hemicellulose were decomposed to formic acid, pyruvic acid, glycolic acid, acetic acid, and lactic acid, whereas lignin was barely decomposed to such organic acids under the given conditions. However, after prolonged treatment (380°C, 100 MPa, 4 min) of lignin, some organic acids were recovered owing perhaps to the decomposition of the propyl side chain of lignin. It was additionally revealed that the predominant organic acid recovered was acetic acid, which might be derived from the acetyl group of hemicellulose in Japanese beech.     

Effect of particle size on pyrolysis characteristics of Elbistan lignite

In this study, the relationship between particle size and pyrolysis characteristics of Elbistan lignite was examined by using the thermogravimetric (TG/DTG) and differential thermal analysis (DTA) techniques. Lignite samples were separated into different size fractions. Experiments were conducted at non-isothermal conditions with a heating rate of 10°C min⁻¹ under nitrogen atmosphere up to 900°C. Pyrolysis regions, maximum pyrolysis rates and characteristic peak temperatures were determined from TG/DTG curves. Thermogravimetric data were analyzed by a reaction rate model assuming first-order kinetics. Apparent activation energy (E) and Arrhenius constant (A _r) of pyrolysis reaction of each particle size fraction were evaluated by applying Arrhenius kinetic model. The apparent activation energies in the essential pyrolysis region were calculated as 27.36 and 28.81 kJ mol⁻¹ for the largest (−2360+2000 μm) and finest (−38 μm) particle sizes, respectively.     

Thermal characteristics of bitumen pyrolysis

The pyrolysis behavior of bitumen was investigated using a thermogravimetric analyzer–mass spectrometer system (TG–MS) and a differential scanning calorimeter (DSC) as well as a pyrolysis-gas chromatograph/mass spectrometer system (Py-GC/MS). TG results showed that there were three stages of weight loss during pyrolysis—less than 110, 110–380, and 380–600 °C. Using distributed activation energy model, the average activation energy of the thermal decomposition of bitumen was calculated at 79 kJ mol⁻¹. The evolved gas from the pyrolysis showed that organic species, such as alkane and alkene fragments had a peak maximum temperature of 130 and 480 °C, respectively. Benzene, toluene, and styrene released at 100 and 420 °C. Most of the inorganic compounds, such as H₂, H₂S, COS, and SO₂, released at about 380 °C while the CO₂ had the maximum temperature peaks at 400 and 540 °C, respectively. FTIR spectra were taken of the residues of the different stages, and the results showed that the C–H bond intensity decreased dramatically at 380 °C. Py-GC/MS confirmed the composition of the evolved gas. The DSC revealed the endothermic nature of the bitumen pyrolysis.     

Evaluation of organic molecules originated during composting process

The composting process using sugarcane bagasse, animal manure, and urea as source of organic matter, microorganism, and nitrogen, respectively, were evaluated regarding the thermal behavior considering the maturation period: 0 (raw), 15, 22, 30, and 60 days. Thermogravimetric and differential thermal analysis curves were obtained in a synthetic air atmosphere and heating rate of 10 °C min⁻¹ in the range of 30–600 °C. The raw compost showed 80% organic matter, which was reduced up to 58% to 60 days compost. Two main mass losses were verified, corresponding to characteristics exothermic peak in differential thermal analysis curves depending on the maturation period. The variation in organic composition was evaluated by Fourier transform infrared spectroscopy verifying the structures (lignin, cellulose, and hemicelluloses) changes with composting process, and the gas chromatography–mass spectrometry was used to identify substance soluble in hexane.     

A kinetic investigation on the pyrolysis of Seguruk asphaltite

The pyrolysis of Seguruk asphaltite has been investigated using thermogravimetric analysis at atmospheric pressure between 293 to 1223 K at different linear heating rates of 5, 10 and 20 K min⁻¹ under nitrogen as ambient gas. There was a two-stage thermal decomposition. Thermal decomposition started around 630 K for stage 1 for the slowest heating rate. On the other hand, for the same heating rate and stage 2, thermal decomposition started around 950 K. These values were shifted to higher temperatures with increasing heating rate. In this study, two different Coats-Redfern methods were applied to thermal degradation of Seguruk asphaltite.     

Study of Thermal Decomposition Kinetics of Low-temperature Reaction of Ammonium Perchlorate by Isothermal TG

The kinetics of the thermal decomposition of ammonium perchlorate at temperatures between 215 and 260°C is studied, in this work, by measuring the sample mass loss as a function of time applying the isothermal thermogravimetric method. From the maximum decomposition rate – temperature dependence two different decomposition stages, corresponding to two different structural phases of ammonium perchlorate, are identified. For the first region (215–235°C), corresponding to the orthorhombic phase, the mean value of the activation energy of 146.3 kJ mol^–1, and the pre-exponential factor of 3.43⋅10¹⁴ min^–1 are obtained, whereas for the second region (240–260°C), corresponding to the cubic phase, the mean value of the activation energy of153.3 kJ mol^–1, and the pre-exponential factor of 4.11⋅10¹⁴ min^–1 are obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

TG-FTIR analysis of switchgrass pyrolysis

Switchgrass is a high yielding perennial grass that has been designated as a potential energy crop. One method of converting switchgrass to energy is by thermochemical conversion to syngas. This requires that the rate of thermal decomposition of switchgrass and the rate of production of components of the syngas be quantified. Ground switchgrass was pyrolyzed at heating rates of 10–40 °C/min in a thermogravimetric analyzer coupled to a Fourier Transform infrared spectrometer. The amount of gases (ppm) that were volatilized during the duration of experiment was quantified. The pyrolysis process was found to compose of four stages: moisture evaporation, hemicellulose decomposition, cellulose decomposition and lignin degradation. The peak temperature for hemicellulose (288–315 °C) and cellulose degradation (340–369 °C) increased with heating rate. FTIR analysis showed that the following gases were given off during the pyrolysis of switchgrass: carbon dioxide, carbon monoxide, acetic acid, ethanol, and methane.