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.     

Thermal stability of ketoprofen��active substance and tablets

Simultaneous thermoanalytical techniques were used for the characterization of the thermal decomposition of ketoprofen??active substance and tablets. DTA and DSC curves showed that ketoprofen melts before the decomposition. A kinetic study regarding the ketoprofen??active substance??s thermal decomposition was performed under non-isothermal conditions and in a nitrogen atmosphere at five heating rates: 2.5, 5, 7.5, 10 and 15 °C min^?1. The kinetic parameters of thermal decomposition process were obtained from TG/DTG curves using the following differential methods: Friedman isoconversional, Chang, respectively, integral methods: Flynn?CWall?COzawa, Kissinger?CAkahira?CSunose, Coats?CRedfern and Madhusudanan. The careful treatment of the kinetic parameters obtained in certain thermal conditions was confirmed to be necessary as well as a different strategy of experimental data processing.     

Pyrolysis and combustion model of oil sands from non-isothermal thermogravimetric analysis data

Thermogravimetric (TG) data of oil sand obtained at Engineering Research Center of Oil Shale Comprehensive Utilization were studied to evaluate the kinetic parameters for Indonesian oil sand samples. Experiments were carried out at heating rates of 5, 15, and 25 °C min^?1 in nitrogen, 10, 20, and 50 °C min^?1 in oxygen atmosphere, respectively. The extent of char combustion was found out by relating TG data for pyrolysis and combustion with the ultimate analysis. Due to distinct behavior of oil shale during pyrolysis, TG curves were divided into three separate events: moisture release, devolatilization, and evolution of fixed carbon/char, where for each event, kinetic parameters, based on Arrhenius theory, were calculated. Coats–Redfern method, Flynn–Wall–Ozawa method, and distributed activation energy model method have been used to determine the activation energies of degradation. The methods are compared with regard to their characteristics and the ease of interpretation of the thermal kinetics. Activation energies of the samples were determined by three different methods and the results are discussed.     

Thermal degradation kinetics of PET/SWCNTs nanocomposites prepared by the in situ polymerization

The decomposition and thermal behavior of poly(ethylene terephthalate) (PET)/carbon nanotubes (CNTs) nanocomposites were studied using thermogravimetric (TG) analysis in air atmosphere. A series of PET/single-walled CNTs (SWCNTs) materials of varying nanoparticles concentration were prepared using the in situ polymerization technique. Transmission electron microscopy and scanning electron microscopy micrographs verified that the dispersion of the SWCNTs in the PET matrix was homogeneous, while some relatively small aggregates co-existed at higher filler concentration. Two-stage decomposition was observed in the experiments. During first stage, strong chemical bonds are broken, i.e., aliphatic bonds and benzyl ring containing molecules decompose into small molecules in the gaseous phase. During second stage, when temperature is higher, the remaining nanotubes along with the residues of the first stage are burned. Kissinger and Coats–Redfern (5, 10, 20, 50 K min^?1) methods were applied to TG data to obtain kinetic parameters (activation energy, Arrhenius constant at 600 K and A factor) and Criado method to kinetics model analysis. In this kinetic model, energy activation is increasing with the increase of nanotubes concentration.     

Thermal characteristics of the combustion process of biomass and sewage sludge

The combustion of two kinds of biomass and sewage sludge was studied. The biomass fuels were wood biomass (pellets) and agriculture biomass (oat). The sewage sludge came from waste water treatment plant. The biomass and sludge percentage in blends with coal were 10 %. The studied materials were characterised in terms of their proximate and ultimate analysis and calorific value. The composition of the ash of the studied fuels was also carried out. The behaviour of studied fuels was investigated by thermogravimetric analysis (TG, DTG and DTA). The samples were heated from an ambient temperature up to 1,000 °C at a constant three rates: 10, 40 and 100 °C min^?1 in 40 mL min^?1 air flow. TG, DTG and DTA analysis showed differences between coal, biomass fuels and sewage sludge. 10 % addition of studied fuels to the mixture with coal changed its combustion profile in the case of sewage sludge addition. The combustion characteristics of fuel mixtures showed, respectively, qualitative summarise behaviour based on single fuels. Evolved gaseous products from the decomposition of studied samples were identified. This study showed that thermogravimetric analysis connected with mass spectrometry is useful techniques to investigate the combustion and co-combustion of biomass fuels, and sewage sludge, together with coal. Non-isothermal kinetic analysis was used to evaluate the Arrhenius activation energy and the pre-exponential factor. The kinetic parameters were calculated using Kissinger–Akahira–Sunose model.     

TG,EGA and kinetic study by non-isothermal decomposition of a polyaniline with different dispersion degree

Polyaniline was obtained by oxidizing aniline in hydrochloric acid media with ammonium peroxidisulfate as oxidizing agent. Molar ratio aniline/oxidant was 1 and aniline/acid ratio: ½, at ?5 and 400 °C, respectively, 800 mL water. The both compounds were studied using two different experimental strategies: the coupled TG-EGA (FTIR) technique by decomposition in dynamic air atmosphere and the kinetic analysis of TG data obtained at four heating rates (5, 7, 10 and 15 K min^?1). The kinetic analysis of the TG non-isothermal data was performed with the Flynn–Wall–Ozawa, Friedman’s, and modified non-parametric kinetic (NPK) methods. By means of the coupled techniques spectroscopic arguments on the reaction mechanism were obtained, i.e. the oxidative degradation of the quinoine ring as the first step. The values of the activation energy by the three used methods are in good agreements. According to the NPK method, the termodegradation process consist in physical (diffusion) and chemical steps.     

Thermal decomposition and kinetics studies on the 2,2-dinitropropyl acrylate–styrene copolymer and 2,2-dinitropropyl acrylate–vinyl acetate copolymer

In the present work, kinetics of thermal decomposition of 2,2-dinitropropyl acrylate–styrene copolymer (DNPA/St) and 2,2-dinitropropyl acrylate–vinyl acetate copolymer (DNPA/VAc) was investigated by differential scanning calorimetry (DSC). The influence of the heating rate (5, 10, 15, and 20 °C min^?1) on the DSC behavior of the copolymer was verified. The results showed that, as the heating rate was increased, decomposition temperature of the copolymer was increased. Also, the kinetic parameters such as activation energy and frequency factor of the copolymer were obtained from the DSC data by the isoconversional methods proposed by Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO). Average activation energy obtained by KAS and FWO methods for the thermal decomposition reaction of DNPA/St and DNPA/VAc are 157.38 ± 0.27 and 147.67 ± 0.57 kJ mol^?1, respectively. The rate constants for thermal decomposition calculated from the activation parameters showed the structural dependency. The relative stability of two copolymers under 50 °C was in this order: DNPA/St > DNPA/VAc. The results of thermogravimetry (TG) analysis revealed that the main mass changes for DNPA/St and DNPA/VAc occurred in the temperature ranges of 200–270 °C. The DSC-FTIR analysis of DNPA/St indicates that the band intensity of nitro and other groups increased haphazardly from 230 °C due to thermal decomposition.     

Effect of the catalyst MCM-41 on the kinetic of the thermal decomposition of poly(ethylene terephthalate)

The aim of this work is to determine the activation energy for the thermal decomposition of poly(ethylene terephthalate)—PET, in the presence of a MCM-41 mesoporous catalyst. This material was synthesized by the hydrothermal method, using cetyltrimethylammonium as template. The PET sample has been submitted to thermal degradation alone and in presence of MCM-41 catalyst at a concentration of 25% in mass (MCM-41/PET). The degradation process was evaluated by thermogravimetry, at temperature range from 350 to 500 °C, under nitrogen atmosphere, with heating rates of 5, 10 and 25 °C min^?1. From TG, the activation energy, determined using the Flynn–Wall kinetic method, decreased from 231 kJ mol^?1, for the pure polymer (PET), to 195 kJ mol^?1, in the presence of the material (MCM-41/PET), showing the catalyst efficiency for the polymer decomposition process.     

Thermal behaviour studies of procaine and benzocaine

The analysed substances, procaine and benzocaine, are two anaesthetic agents currently being administered in tablet form, also in the topical (cream, gel, balm) and injectable dosage forms. The TG/DTG/DTA curves were obtained in air at different heating rates. For determination of the heat effects, the DTA curves (in μV) were changed with the heat flow curves (in mW), so that the peak area corresponds to an energy in J g^?1 or kJ mol^?1. The non-isothermal experiments are preformed to investigate the thermal degradation process of these active substances, both as a solid and are performed in a dynamic atmosphere of air at different heating rates, by heating from room temperature to 500 °C. The kinetic analysis was performed using the TG data in air for the first step of substance’s decomposition at four heating rates: 7, 10, 12 and 15 °C min^?1. The data were processed according to an appropriate strategy to the following kinetic methods: Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, Friedman and NPK, to obtain realistic kinetic parameters, even if the decomposition process is a complex one. Thermal analysis was supplemented using Fourier Transform infrared spectroscopy coupled with the TG device to identify the anaesthetics with any products which may have formed (EGA—the evolved gas analysis).     

Studies on the thermal behavior and decomposition kinetic of drugs cetirizine and simvastatin

Understanding the response of drugs and their formulations to thermal stresses is an integral part of the development of stable medicinal products. In the present study, the thermal degradation of two drug samples (cetirizine and simvastatin) was determined by differential scanning calorimetery (DSC) and simultaneous thermogravimetery/differential thermal analysis (TG/DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the cetirizine occurs during two temperature ranges of 165–227 and 247–402 °C. The TG/DTA analysis of simvastatin indicates that this drug melts (at about 143 °C) before it decomposes. The main thermal degradation for the simvastatin occurs during two endothermic behaviors in the temperature ranges of 238–308 and 308–414 °C. The influence of the heating rate (5, 10, 15, and 20 °C min^?1) on the DSC behavior of both the drug samples was verified. The results showed that as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Based on the values of activation energy obtained by ASTM E696 method, the values of activation energy for cetirizine and simvastatin were 120.8 and 170.9 kJ mol^?1, respectively. Finally, the values of ΔS ^#, ΔH ^#, and ΔG ^# of their decomposition reaction were calculated.     

Thermal analysis kinetics of thermal decomposition of nickel–viscose composite fiber

In this study, the thermal decompositions of nickel composite fibers (NCF) under different atmospheres of flowing nitrogen and air were investigated by XRD, SEM–EDS, and TG–DTG techniques. Non-isothermal studies indicated that only one mass loss stage occurred over the temperature regions of 298–1,073 K in nitrogen. The mass loss was from the decomposition. But after this decomposition, nickel was oxidized in air, when the temperature was high enough. In nitrogen media, the model-free kinetic analysis method was applied to calculate the apparent activation energy (E _a) and pre-exponential factor (A). The method combining Satava–?esták equation with one TG curve was used to select the suitable mechanism functions from 30 typical kinetic models. Furthermore, the Coats–Redfern method was used to study the NCF decomposition kinetics. The study results showed that the decomposition of NCF in nitrogen media was controlled by three-dimension diffusion; mechanism function was the anti-Jander equation, the apparent activation energy (E _a) and the pre-exponential factor (A) were 172.3 kJ mol^?1 and 2.16 × 10⁹ s^?1, respectively. The kinetic equation could be expressed as following: $$ \frac{{{\text{d}}\alpha }}{{{\text{d}}T}} = \frac{{ 2. 1 6\times 1 0^{ 9} }}{\beta }{ \exp }\left( {\frac{ - 2 0 7 2 4. 1}{T}} \right)\left\{ {\frac{ 3}{ 2}(1 + \alpha )^{2/3} [(1 + \alpha )^{1/3} - 1]^{ - 1} } \right\}. $$      

Thermal properties and kinetics of new-generation posterior bulk fill composite cured light-emitting diodes

In this study, the thermal behavior in terms of glass transition (T _g), degradation, and thermal stability of four commercial new-generation posterior bulk fill composites (Surefill SDR, Dentsply; Quixfill, Dentsply; Xtrabase, Voco; and Xtrafill, Voco) activated by light-emitting diodes (LEDs) was analyzed by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The activation energies (E _a) for the decomposition of the dental resins were calculated based on the Kissinger and Doyle kinetic models from the peaks of the endothermic curves obtained when the specimens were heated at four different temperatures (5, 10, 15, and 20 °C min^?1) during DSC. The results show that the Xtrabase composite displayed the highest T _g (120 °C at a 5 °C min^?1 heating rate) and E _a (157.64 kJ mol^?1) values associated with thermal degradation from the main chain of the polymer.     

Thermal analysis of Beypazari lignite

Beypazari lignite was investigated by differential scanning calorimetry (DSC), thermogravimetry (TG), high pressure thermogravimetry (HPTG) and combustion cell experiments. All the experiments were conducted at non-isothermal heating conditions with a heating rate of 10°C min^?1, in the temperature range of 20–700°C. DSC-TG data were analysed using an Arrhenius-type reaction model assuming a first-order reaction. For the HPTG data the Coats and Redfern equation was used for kinetic analysis. In the combustion cell experiments the Fassihi and Brigham approach was used in order to calculate kinetic data. Finally a comparison is made between the kinetic results.     

Investigation of thermal decomposition kinetics of taurine

The non-isothermal thermal decomposition of taurine was investigated by means of thermogravimetric analysis (TG) and differential thermal analysis (DTA). The experimental data were treated using Flynn–Wall–Ozawa, Doyle, Kissinger, and ?atava–?esták methods, respectively. The results show that the non-isothermal thermal decomposition mechanism of taurine is classified as phase boundary reaction, and the mechanism function is the Mampel Power law with n = 1. The forms of both integral and differential for the mechanism function are $ G(\alpha ) = \alpha $ and $ f(\alpha ) = 1 $ , respectively. The activation energy and the pre-exponential factor are 167.88 kJ mol^?1 and 1.82 × 10¹³min^?1, respectively.     

Kinetic analysis for non-isothermal decomposition of un-irradiated and gamma-irradiated potassium bromate

The thermal decomposition of un-irradiated and gamma-irradiated potassium bromate (KBrO₃) was performed under non-isothermal conditions at different heating rates (5, 10, 15 and 20 K min^?1). The data was analysed using isoconversional and non-isoconversional methods. The kinetic parameters of thermal decomposition process were obtained by three model-free isoconversional methods: Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Friedman. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy decreases on irradiation. Kinetic analysis of data in view of various solid-state reaction models showed that the decomposition of un-irradiated and irradiated anhydrous KBrO₃ is best described by the Avrami–Erofeev model equation, [?ln(l?α)]^1/2 = kt.     

An experimental study on thermal decomposition behavior of magnesite

Thermal decomposition of magnesite is investigated by using a TG–MS. Different kinetic methods including Coats–Redfern, Flynn–Wall–Ozawa, and Kissinger–Akahira–Sunose are used to investigate the thermal decomposition kinetics of magnesite. It was observed that the activation energy values obtained by these methods are similar. The average apparent activation energy is found to be about 203 kJ mol^?1. The raw magnesite and its decomposition products obtained at different temperatures are analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM). The concentration of functional groups, crystal structure and composition, and apparent morphology of decomposition products were studied in detail. The FTIR, XRD, and SEM analyses showed that magnesite was completely decomposed at 973 K to form MgO.     

Thermal study on decomposition of LiBH4 at non-isothermal and non-equilibrium conditions

Thermal decomposition measurements for lithium borohydride (LiBH₄) are performed at non-isothermal and non-equilibrium conditions by means of differential thermal analysis (DTA). A simplified alternative procedure is introduced for evaluating thermodynamic and kinetic parameters simultaneously using a single set of measurements. Rate constant (k) and enthalpy (ΔH = ?102.1 ± 0.7 kJ mol^?1 LiBH₄) are archived. Temperature dependence for activation energy (E _a) is found taking advantage of Guggenheim–Arrhenius method; the mean activation energy is $ \overline{E}_{a} $  93.9 ± 0.9 kJ mol^?1 LiBH₄ in the range of heating rate β 1–50 K min^?1.     

Thermal parameters study of 1,1-bis(tert-butylperoxy)cyclohexane at low heating rates with differential scanning calorimetry

Having two active peroxide groups, 1,1-bis(tert-butylperoxy)cyclohexane (BTBPC) has a certain degree of thermal instability. It is usually used as an initiator in a chemical process, and therefore, careless operation could result in severe accidents. This study emphasized the runaway reactions of BTBPC 70 mass% (4.5–5.2 mg), the relevant thermokinetic parameters, and the thermal safety parameters. Differential scanning calorimetry was used to evaluate the above-mentioned thermokinetic parameters, using four low heating rates (0.5, 1, 2, and 4 °C min^?1) combined with kinetic simulation method. The results indicated that apparent exothermic onset temperature (T _o), apparent activation energy (E _a), and heat of decomposition (ΔH _d) were ca. 118 °C, 156 kJ mol^?1, and 1,080 kJ kg^?1, respectively. In view of process loss prevention, at the low heating rates of 0.5, 1, 2, and 4 °C min^?1, storing BTBPC 70 mass% below 27.27 °C is a more reassuring approach.     

Comparative kinetics studies of thermal decomposition of kalium, respectively natrium oxalato-oxo-diperoxo molibdate

The aim of this paper is to present the comparative kinetics of thermal decomposition of K₂[MoO(O₂)₂(C₂O₄)] (kalium oxalato-oxo-diperoxo molibdate), respectively Na₂[MoO(O₂)₂(C₂O₄)] (natrium oxalato-oxo-diperoxo molibdate). The TG data were obtained at different heating rates: β = 2.5, 4, 5, and 10 °C min^?1 in air and nitrogen (50 mL min^?1), and the TG/DTG data were processed with the following methods: Friedman, Flynn–Wall–Ozawa and modified-NPK method.     

Thermal decomposition of tetraalkylammonium iodides

A number of tetramethylammonium (TMA) iodides, including mono-, tri-, and pentaiodide, were synthesized. Thermal decomposition of samples was investigated by simultaneous TG–DSC analysis accompanied by gaseous IR- and mass-spectrometry analyses. Two different reaction pathways have been observed for TMA pentaiodide at different heating rates. At low heating rates (1–5 K min^?1), a gradual mass loss takes place and a stability plateau due to monoiodide formation exists on TG curve. At high heating rates (10, 15 and 7 K min^?1 as the in-between stage), there are only two peaks on DTG curve (instead of three for lower heating rates) and no monoiodide formation is observed as the sample decomposes completely before 350 °C.