Model-free method for isothermal and non-isothermal decomposition kinetics analysis of PET sample

Pyrolysis, one possible alternative to recover valuable products from waste plastics, has recently been the subject of renewed interest. In the present study, the isoconversion methods, i.e., Vyazovkin model-free approach is applied to study non-isothermal decomposition kinetics of waste PET samples using various temperature integral approximations such as Coats and Redfern, Gorbachev, and Agrawal and Sivasubramanian approximation and direct integration (recursive adaptive Simpson quadrature scheme) to analyze the decomposition kinetics.The results show that activation energy (E_α) is a weak but increasing function of conversion (α) in case of non-isothermal decomposition and strong and decreasing function of conversion in case of isothermal decomposition. This indicates possible existence of nucleation, nuclei growth and gas diffusion mechanism during non-isothermal pyrolysis and nucleation and gas diffusion mechanism during isothermal pyrolysis. Optimum E_α dependencies on α obtained for non-isothermal data showed similar nature for all the types of temperature integral approximations.     

Comparative kinetic study of decomposition of some diazepine derivatives under isothermal and non-isothermal conditions

Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances. TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability, compatibility, polymorphism, kinetic analysis, phase transitions etc.). The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric kinetics. In the model-fitting methods the kinetic triplets (f(α), A and E _a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation energies on the extent of conversion. It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous work. The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as well as a different strategy of experimental data processing.     

Mechanisms and kinetics of thermal decomposition of plastics from isothermal and dynamic measurements

The kinetics of decomposition of plastics are of interest from different points of view, i.e. evolution of harmful substances during fires or waste incineration, recovering of chemical raw materials from plastic refuses and designing of recycling procedures. To measure the formal kinetic parameters of the degradation of polymers isothermal and dynamic methods are applied in this work. Dynamic measurements are performed by combined thermogravimetry mass spectrometry (TG-MS), the isothermal measurements are carried out with a new closed loop-type reactor. To evaluate consistent kinetic data from isothermal and dynamic measurements, the energy balance for the sample in dynamic measurements has to be considered to obtain the true sample temperature and heating rate. Subject of this investigation is the exploitation of dynamic and isothermal methods for measuring and interpreting the kinetics of thermal decomposition of plastics. Results for commodity plastics polyethylene and poly(vinyl chloride) (PVC) are presented. The combined application of TG–MS, isothermal experiments in the closed loop-type reactor and DSC leads to new results for the decomposition kinetics of PVC. The dehydrochlorination mechanism at moderate temperature can be distinguished in an endothermal and exothermal part. The benzene formation is identified as a second order reaction. A great advantage of the isothermal method is, that changes in the mechanisms are detectable, i.e. changes in the apparent order of the reaction and the apparent activation energy. From that, new mechanistic aspects of the decomposition kinetics of polyethylene were obtained.     

Studies of thermal decomposition of palladium(II) complexes with olefin ligands

Thermal decomposition kinetics of ML₂ (M = Ni(II) and Co(II); L = 5-(2-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)hydrazono)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione) complexes were investigated by thermogravimetric analysis (TGA). The first decomposition process of the NiL₂ and CoL₂ complexes occurs in the temperature range of 320–350 °C. Kinetics parameters corresponding to this step, such as activation energy, E_α, and apparent pre-exponential factor, ln A_aap, were calculated from the thermogravimetric data at the heating rates of 5, 10, 15 and 20 K min⁻¹ by differential (Friedman's equation) and integral (Flynn–Wall–Ozawa's equation) methods. The results show that the activation energy evidently depends on the extent of conversion. As far as their activation energy is concerned, NiL₂ complex shows a higher thermal stability than the CoL₂ complex.     

Non-isothermal kinetic applied to thermal decomposition of commercial alkyd varnish

Summary PHB polyester poly(3-hydroxybutyrate) is an interesting biodegradable polymer and intensively investigated as cast and sheet films with applications in food industry or in medicine. The films obtained are typically brittle and many scientists have attempted to reduce this brittleness by blending with other polymers. PHB from Usina da Pedra was blended with PEG poly(ethyleneglycol) 300 resulting in blend 1 and blend 2. The two mixtures were melted at 200 and quenched at 0°C. TG curves showed that the thermal stability of the blends and the PHB are identical. For these blends the crystallization temperature decreased compared to the pure PHB, which is probably due to the lower nucleation density.     

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 applied to the characterization of degradation in soil of polylactide: II. On the thermal stability and thermal decomposition kinetics

The disposal stage of polylactide (PLA) was assessed by burying it in active soil following an international standard. Degradation in soil promotes physical and chemical changes in the polylactide properties. The characterization of the extent of degradation underwent by PLA was carried out by using Thermal Analysis techniques. In this paper, studies on the thermal stability and the thermal decomposition kinetics were performed in order to assess the degradation process of a commercial PLA submitted to an accelerated soil burial test by means of multi-linear-non-isothermal thermogravimetric analyses. Results have been correlated to changes in molecular weight, showing the same evolution as that described by the parameters of thermal stability temperatures and apparent activation energies. The decomposition reactions can be described by two competitive different mechanisms: Nucleation model (A2) and Reaction Contracting Volume model (R3). The changes in the kinetic parameters and kinetic models are in agreement with the calorimetric and dynamic-mechanical-thermal results, presented in the Part I of the study [1].     

Tin(II)-EDTA complex: kinetic of thermal decomposition by non-isothermal procedures

Tin on the oxide form, alone or doped with others metals, has been extensively used as gas sensor, thus, this work reports on the preparation and kinetic parameters regarding the thermal decomposition of Sn(II)-ethylenediaminetetraacetate as precursor to SnO₂. Thus, the acquaintance with the kinetic model regarding the thermal decomposition of the tin complex may leave the door open to foresee, whether it is possible to get thin film of SnO₂ using Sn(II)-EDTA as precursor besides the influence of dopants added.The Sn(II)-EDTA soluble complex was prepared in aqueous medium by adding of tin(II) chloride acid solution to equimolar amount of ammonium salt from EDTA under N₂ atmosphere and temperature of 50 °C arising the pH∼4. The compound was crystallized in ethanol at low-temperature and filtered to eliminate the chloride ions, obtaining the heptacoordinated chelate with the composition H₂SnH₂O(CH₂N(CH₂COO)₂)₂·0.5H₂O.Results from TG, DTG and DSC curves under inert and oxidizing atmospheres indicate the presence of water coordinated to the metal and that the ethylenediamine fraction is thermally more stable than carboxylate groups. The final residue from thermal decomposition was the SnO₂ characterized by X-ray as a tetragonal rutile phase.Applying the isoconversional Wall-Flynn-Ozawa method on the DSC curves, average activation energy: E_a=183.7±2.7 and 218.9±2.1 kJ mol⁻¹, and pre-exponential factor: and 19.10±0.27 min⁻¹, at 95% confidence level, could be obtained, regarding the loss of coordinated water and thermal decomposition of the carboxylate groups, respectively. The E_a and log A also could be obtained applying isoconventional Wall-Flynn method on the TG curves.From E_a and log A values, Dollimore and Malék procedures could be applied suggesting R3 (contracting volume) and SB (two-parameter model) as the kinetic model to the loss of coordinated water (177-244 °C) and thermal decomposition of the carboxylate groups (283-315 °C), respectively. Simulated and experimental normalized DTG and DSC curves besides analysis of residuals check these kinetic models.     

Synthesis and kinetic analysis of isothermal and non-isothermal decomposition of ammonium dinitramide prills

Ammonium dinitramide (ADN) prills were prepared by emulsion crystallization and characterized by optical microscopic, thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques. The isothermal and non-isothermal decomposition kinetics of ADN prills were studied by TG. The differential isoconversional method of Friedman (FR) and integral isoconversional method of Vyazovkin were used to investigate the dependence of activation energy (E _a) with conversion (α) and the results were compared with literature data. The dependence of activation energy was also derived from isothermal data. A strong dependence of E _a with α is observed for the ADN prills. All the methods showed an initial increase in E _a up to α=∼0.2 and later decreases over the rest of conversion. The apparent E _a values of FR method are higher than that of Vyazovkin method up to α=∼0.45. The calculated mean E _a values by FR, Vyazovkin and standard isoconversional method for α between 0.05 and 0.95 were 211.0, 203.9 and 156.9 kJ mol⁻¹, respectively.     

Comparative method to evaluate reliable kinetic triplets of thermal decomposition reactions

Reliable kinetic information for thermal analysis kinetic triplets can be determined by the comparative method: (1) An iterative procedure or the KAS method had been established to obtain the reliable value of activation energy E _a of a reaction. (2) A combined method including Coats-Redfern integral equation and Achar differential equation was put forward to confirm the most probable mechanism of the reaction and calculate the pre-exponential factor A. By applying the comparative method above, the thermal analysis kinetic triplets of the dehydration of CaC₂O₄·H₂O were determined, which apparent activation energy: 81±3 kJ mol^-1, pre-exponential factor: 4.51·106-1.78·10⁸ s^-1, the most probable mechanism function: f(α)=1 or g(α)=α, which the kinetic equation of dehydration is dα/dt=Ae^-E _a ^/RT. This revised version was published online in August 2006 with corrections to the Cover Date.     

Self-assembled CuO nanoarchitectures and their catalytic activity in the thermal decomposition of ammonium perchlorate

CuO shuttle-like and flower-like nanocrystals were synthesized through a one-step, low-temperature solution-phase method in the presence of a cation surfactant, hexadecyl trimethyl ammonium bromide. These nanocrystals were studied as an additive for promoting the thermal decomposition of ammonium perchlorate (AP). With the addition of CuO shuttle-like and flower-like nanocrystals, the thermal decomposition temperature of AP decreased. The structure, particle size, and morphology of resulting CuO powders were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis technique was applied to investigate the thermal decomposition of mixtures of AP and as-prepared CuO nanocrystals.     

Assessment of various kinetic models for the pyrolysis of a microgranular cellulose

The kinetics of pyrolysis of a micro-crystalline cellulose in nitrogen were studied from TGA and DTG data, obtained with two different modes of heating: a dynamic mode at constant heating rates between 1 and 11 °C/min and an isothermal mode at various temperatures, kept constant between 280 and 320 °C. In isothermal mode, it appeared very clearly that the mass depletion shows a sigmoid profile characteristic of an auto-accelerated reaction process. This behaviour is consistent with kinetics of nuclei-growth, well represented by the models of Avrami-Erofeev (A-E) and of Prout-Tompkins (P-T) type. All the other kinetic models commonly applied to the thermal decomposition of solids revealed unsatisfactory. The TGA and DTG data were, thus, found ideally simulated from a reaction scheme consisting in two parallel reactions, termed 1 and 2, each one described by the kinetic law: dx/dt=−A^−E/RTxⁿ(1−0.99x)^m. Reaction 1 is related to the bulk decomposition of cellulose and is characterised by the set of parameters: E₁=202 kJ/mol; n₁=1; m₁=0.48. Reaction 2 is related to the slower residual decomposition, which takes place over approximately 350 °C and affects only 16% by weight of the raw cellulose. With m₂ constrained to 1, the optimised parameters of this reaction were: E₂=255 kJ/mol; n₂=22. Finally, the proposed model allowed to correctly fit not less than to 10 sets of ATG-DTG data, isothermal and dynamic.     

Enhancement of thermal properties of Kevlar 29 coated by SiC and TiO2 nanoparticles and their binding energy analysis

In the fields of military research, aerospace, and vehicle technology, the thermal stability of Kevlar fiber is critical for improving its flame resistance. In this work, the pad mangle machine was used to improve the thermal properties of Kevlar 29 in order to expand the range of applications for thermal aspects. Silicon carbide and titanium oxide nanoparticles provide thermal stability on the fiber surface through intermolecular adhesion. Here, 5 wt% and 10 wt% of nanoparticles with various mass ratios (1:1) have been chosen. Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) analysis, and X-ray Photoelectron Spectroscopy (XPS) analysis have all been used to measure different thermal properties. The surface morphology of samples is represented by FESEM analysis, while the active organic groups are represented by FTIR analysis. The greater crystallization of epoxy and nanoparticles is linked to post-heat treatment of the material. The glass transition temperature of the coated samples shifted maximum from 559.13 °C to 580.51 °C, the end set temperature increased by 30.67 °C compared to the uncoated sample, and the residual weight changed from 29.77 percent to 4.06 percent, according to the findings (i.e., lightweight). When compared to the uncoated sample, the coated sample's enthalpy increased significantly (i.e., the samples can absorb more heat). The smaller the positive binding energy, the higher the activation energy, and hence the slower the chemical reaction, which is especially important in high-temperature applications. Finally, this research reveals a 4.5–5.2 percent increase in thermal characteristics.     

Controlled thermal decomposition of NaSi to derive silicon clathrate compounds

Formation conditions of two types of sodium containing silicon clathrate compounds were determined by the controlled thermal decomposition of sodium monosilicide NaSi under vacuum. The decomposition began at 360 °C. Much higher decomposition temperatures and the presence of sodium metal vapor were favorable for the formation of type I clathrate compound Na₈Si₄₆. Type II clathrate compound Na_xSi₁₃₆ was obtained as a single phase at a decomposition temperature <440 °C under the condition without sodium metal vapor. The type I clathrate compound was decomposed to crystalline Si above 520 °C. The type II clathrate compound was thermally more stable, and retained at least up to 550 °C in vacuum.     

The correctional kinetic equation for the peak temperature in the differential thermal analysis

The peak temperature (T _p) and different temperature (ΔT) are the basic information in the differential thermal analysis (DTA). Considering the kinetic relation and the heat equilibrium in DTA, a correctional differential kinetic equation (containing T _p and ΔT parameter) is proposed. In the dehydration reaction of CaC₂O₄·H₂O, the activation energy calculated from the new equation showed some smaller than that from Kissinger equation, but some bigger than that from Piloyan equation.     

Non-isothermal kinetic study on the decomposition of Zn acetate-based Sol-gel precursor

The isoconversional methods (Friedman (FR), Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS)) were applied for evaluating the dependencies of the activation energy (E) on the mass loss (Δm) corresponding to the non-isothermal decomposition of two Zn acetate-based gel precursors for ZnO thin films whose preparation differs by the drying temperature of the liquid sol-precursor (125°C for sample A, and 150°C for sample B). Although both investigated samples exhibit similar decomposition steps, strong differences between E vs. Δm curves as well as among the characteristic parameters of the decomposition steps, directly evaluated from TG, DTG and DTA curves, were put in evidence.     

Thermodynamic,kinetic and surface texture factors in the production of active solids by thermal decomposition

The production of an active solid by thermal decomposition of some precursor material usually an oxysalt is only one way of producing such a material. The activity of any solid resides at the surface albeit some of the surface may be internal or in the decomposition process a reaction interface. The peculiar property of any solid phase is that to describe it properly one must cite the pre-history of the material, and it can be shown that the pre-history of any solid phase is mainly that of altering the surface and textural properties. This fact influences the application of thermodynamic and kinetics to processes involving the solid phase. This becomes more evident in the case of active solids where a larger proportion of chemical species than usual resides at or near the surface. This is evidenced by the existence of many or more active solids in an amorphous phase and the possible co-existence of different types of solid phase. In this review, the usefulness of normal solid phase structural determination is discussed and the manner in which thermal analysis can be used to determine thermodynamic and kinetic parameters.

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Zusammenfassung Die Herstellung eines aktiven Feststoffes durch thermische Zersetzung einiger Präkursorsubstanzen, meistens eines Oxysalzes, ist nur der eine Weg zur Herstellung solcher Substanzen. Die Aktivität der Feststoffe besteht an ihrer Oberfläche, obwohl sich ein Teil der Oberfläche auch im Innern oder bei Zersetzungsprozessen an der Reaktionsgrenzfläche befinden kann. Die eigentümliche Eigenschaft einiger Feststoffphasen besteht darin, da\ man, um sie richtig beschreiben zu können, die Vorgeschichte der Substanz berücksichtigen mu\ und es kann gezeigt werden, da\ die Vorgeschichte einer Substanz hauptsächlich die der Veränderung der Oberflache und der Feinstruktur ist. Diese Tatsache beeinflu\t die Anwendung von Thermodynamik und Reaktionskinetik bei Prozessen mit Feststoffen. Dies ist besonders bei aktiven Feststoffen offensichtlich, bei denen an oder in der Nähe der Oberfläche verhältnismä\ig mehr chemische Stoffe vorkommen als üblicherweise. Dies wird durch die Existenz von vielen oder mehreren aktiven Feststoffen in einer amorphen Phase und durch die mögliche Koexistenz verschiedenartiger Festphasen bezeugt. In vorliegendem überblick wird die Nützlichkeit der Strukturbestimmung normaler Feststoffphasen sowie die Art der möglichen Anwendung der Thermoanalyse bei der Bestimmung thermodynamischer und kinetischer Parameter diskutiert.

     

吸热型碳氢燃料正癸烷热裂解机理、热沉及产物分布的理论研究

采用密度泛函理论(DFT)的B3LYP方法在6-311G(d,p)基组水平上对正癸烷裂解过程中涉及的反应物、产物及过渡态进行了几何构型优化和振动频率计算,运用B3LYP/aug-cc-pVTZ方法计算单点能并构建势能剖面图。利用TheRate程序包及Eckart校正模型计算了各反应速率常数k。采用统计热力学原理求得不同温度下的热容C_p,m^θ及熵S_{298 K}^θ,并通过设计等键反应获得了各物种的标准生成焓△_fH_{298 K}^θ。用Chemkin II程序模拟预测了产物分布,理论计算了热沉值,并讨论了温度、压力对产物分布和热沉的影响。结果表明,C-C键断裂过程是反应的初始步骤,且抽氢反应较β键断裂反应更易进行。裂解起始温度为500 ℃,反应主要发生在600~700 ℃,其主要产物为氢气、甲烷、乙烯、乙烷、丙烯和1,3-丁二烯,且产物分布随温度不同而变化。模拟计算获得正癸烷在温度600 ℃、压力2.5 MPa条件下的总热沉值为2.334 MJ/kg,对应的热裂解转化率为25.9%,该热沉值可以满足速率为5~6马赫数的飞行器的冷却要求。     

Role of isoconversional methods in varying activation energies of solid-state kinetics: I. isothermal kinetic studies

Solid-state kinetics was developed from kinetic concepts for reactions in homogeneous phase systems, which has created considerable debate over issues such as variable activation energy. This behavior has been viewed by some as a violation of basic chemical kinetic principles. Variation in activation energy has been detected by isoconversional or ‘model-free’ calculation methods. The relationship between different calculation methods and the occurrence of variable activation energy was investigated in this work by employing model-fitting and isoconversional methods to analyze simulated isothermal data. In addition, these approaches were applied for sulfameter-dioxolane solvate desolvation data. We showed that variable activation energy is of two types—a true variation that results from the complex nature of the solid-state process and an artifactual one resulting from the use of some isoconversional methods.