Model-free Kinetic Analysis Research Articles

Model-free kinetic analysis of multi-step thermal decomposition of ammonium perchlorate coated with reduced graphene oxide

Model-free kinetic analysis of multi-step thermal decomposition of ammonium perchlorate coated with reduced graphene oxide

Kinetic study of sesame stalk pyrolysis by thermogravimetric analysis

Sesame stalk is a promising agricultural residue for generating renewable bioenergy, but still remains undeveloped on account of the lack of reliable pyrolysis kinetic information. The novelty of present work lies in that it gives the first thorough examination of kinetic and thermodynamic parameters for pyrolysis of sesame stalk. Non-isothermal pyrolysis experiments in N2 via thermogravimetric analysis were conducted at 5–20 K/min with temperatures programmed from 350 to 900 K. Experimental results indicate that pyrolysis of sesame stalk seems to occur in multi-stage reactions, model-free kinetic analysis methods, including differential Friedman, integral Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa and Vyazovkin-Dollimore methods, are isoconversionally attempted to perform kinetic analysis of two-stage sesame stalk pyrolysis, respectively resulting in the mean activation energy of 136, 125, 128 and 125 kJ/mol for stage I and 140, 146, 150 and 146 kJ/mol for stage II. The master-plots method and differential composite method are integrated for determining pyrolysis mechanism, and the Ginstling−Brounshtein model is found to be the most appropriate and verified very well by experimental results. The averaged pre-exponential factors for two stages are determined to be 2.80 × 108 and 1.04 × 109 min−1, respectively. Besides, thermodynamic parameters in terms of ΔH, ΔG and ΔS are also evaluated for the whole pyrolysis process. The findings acquired from this study suggest sesame stalk is a promising biomass for sustainable bioenergy generation and kinetic and thermodynamic information is of significance for advancing the design of a sesame stalk pyrolysis reactor.

Thermal decomposition characterization and kinetics of copper, iron, manganese and zinc chelates of ethylenediaminetetraacetic acid in air atmosphere

The analysis of the thermal stability of Cu, Fe, Mn, and Zn-EDTA (copper, iron manganese, and zinc chelates of ethylenediaminetetraacetic acid) chelates indicates a high complexity of occurring decomposition processes, ranging from two to three simplified stages of the decomposition process. Obtained results reports that the thermal stability decreased in the following order: Zn-EDTA > Mn-EDTA > Cu-EDTA > Fe-EDTA. The initial model-free kinetic analysis suggested that three out of four chelates had a multi-step first stage of the decomposition. Model-fitting methodology resulted in the best fit in the first stage of decomposition of the studied EDTA chelates that corresponded to An (nth-dimensional nucleation) or Cn (nth-order autocatalytic reaction) models with correlation coefficients within 0.9951 to 0.9991. The activation energy values were within the range 126.27–253.25 kJ·mol−1. The least stable chelates, Cu and Fe, were defined by using competitive An and Cn reaction types, while the most stable, Zn, has a single-step Cn first stage of the decomposition process. The study showed the initial possibility of using EDTA chelates of zinc, manganese, and possibly copper in fertilizer production.

Kinetic Analysis for the Catalytic Pyrolysis of Polypropylene over Low Cost Mineral Catalysts

A kinetic analysis of non-catalytic pyrolysis (NCP) and catalytic pyrolysis (CP) of polypropylene (PP) with different catalysts was performed using thermogravimetric analysis (TGA) and kinetic models. Three kinds of low-cost natural catalysts were used to maximize the cost-effectiveness of the process: natural zeolite (NZ), bentonite, olivine, and a mesoporous catalyst, Al-MCM-41. The decomposition temperature of PP and apparent activation energy (Ea) were obtained from the TGA results at multiple heating rates, and a model-free kinetic analysis was performed using the Flynn–Wall–Ozawa model. TGA indicated that the maximum decomposition temperature (Tmax) of the PP was shifted from 464 °C to 347 °C with Al-MCM-41 and 348 °C with bentonite, largely due to their strong acidity and large pore size. Although olivine had a large pore size, the Tmax of PP was only shifted to 456 °C, because of its low acidity. The differential TG (DTG) curve of PP over NZ revealed a two-step mechanism. The Tmax of the first peak on the DTG curve of PP with NZ was 376 °C due to the high acidity of NZ. On the other hand, that of the second peak was higher (474 °C) than the non-catalytic reaction. The Ea values at each conversion were also decreased when using the catalysts, except olivine. At <0.5 conversion, the Ea obtained from the CP of PP with NZ was lower than that with the other catalysts: Al-MCM-41, bentonite, and olivine, in that order. The Ea for the CP of PP with NZ increased more rapidly, to 193 kJ/mol at 0.9 conversion, than the other catalysts.

Material extrusion based additive manufacturing of large zirconia structures using filaments with ethylene vinyl acetate based binder composition

This study demonstrates the feasibility of fabricating large complex zirconia structures using a material extrusion-(MEX) based additive manufacturing process, called fused deposition modeling (FDM) or fused filament fabrication (FFF). For this purpose, a feedstock based on ethylene-vinyl acetate and stearic acid containing 45 vol.-% zirconia powder was extruded into filaments and used for printing on a consumer-grade FDM/FFF printer. To detect structural failures after each processing step, disks made out of 4 printed layers were selected. After printing, debinding and sintering a fractography analysis of the disks was evaluated using an optical and scanning electron microscope to identify the defects. To avoid defect formation during printing, a new approach, dynamic infill technique, was employed and resulted in void-free printed disks with a smooth top surface. This approach was essential to study the origin of failures in the post-processing steps. Model free-kinetic analysis was used to investigate the activation energy of the binder decomposition and to design a thermal debinding program with a constant 0.1%/min mass loss rate of the thermoplastic binder. Based on the kinetic studies it could be demonstrated that sufficient thermal binder burnout could be achieved by integration of solvent extraction and wicking debinding steps. Using ring-on-ring test it could be observed, that an edge-initiated failure resulted in low average strength (91 MPa) of the sintered disks. Finally, printed and defect-free sintered 120 mm high vase could be successfully achieved using the model free-kinetic designed debinding program. • Development of a dynamic infill approach in printing to eliminate print failures. • Designing an efficient debinding program using kinetic modeling. • Evaluating mechanical properties of printed disks using ring-on-ring method. • Characterizing failure origins using fractography on broken disks. • Printing/debinding/sintering of a 120 mm high zirconia vase structure.

Optimization of a commercial epoxy curing cycle via DSC data kinetics modelling and TTT plot construction

A commercial bio-epoxy resin was investigated by means of DSC experiments. Dynamic ramps of 1, 2.5, 5 and 10 °C/min were used to attain the total heat of curing reaction (ΔHtotal) and glass transition temperatures of the unreacted monomers (Tgo) and the fully cured sample (Tgoo), estimated to be 398.3 J/gr, −46.4 °C and 63.9 °C, respectively. Isothermal measurements at 50, 65, 70 and 80 °C were performed in order to construct Di Benedetto equation, which resulted in the values of −44.1 °C and 61.2 °C for Tgo and Tgoo. Isothermal predictions, based solely on dynamic DSC data, were further conducted. Model-free kinetic analysis revealed a slight decrease in the effective activation energy Eα, which found to vary with conversion in the range of 30–60 kJ/mol. Utilizing Kamal and Sourour (KS) with diffusion reaction model under dynamic conditions, Ea values of 49 kJ/mol and 56 kJ/mol were reported for catalytic and autocatalytic mechanism, while a strong compliance was accomplished between experiment and simulation. Vyazovkin isoconversional method accurately predicted isothermal curing for temperatures exceeding 65 °C, could not however capture curing rate hindrance below Tgoo. Eventually, KS with diffusion model was incorporated in the production of Time Temperature Transformation (TTT) plot. The present comprehensive kinetic analysis, aims for divulging the optimum curing temperature window for the investigated epoxy system, leading the way to materials with advanced properties.

A Comparative Study on Suitability of Model-Free and Model-Fitting Kinetic Methods to Non-Isothermal Degradation of Lignocellulosic Materials.

The thermal kinetic modeling is crucial for development of sustainable processes where lignocellulosic fuels are a part of chemical system and their thermal degradation eventuates. In this paper, thermal decomposition of three lignocellulosic materials (bagasse, rice husk, and wheat straw) was obtained by the thermogravimetric (TG) technique and kinetics was analyzed by both model-fitting and isoconversional (model-free) methods to compare their effectiveness. Two models selected from each class include Arrhenius and Coats–Redfern (model-fitting), and Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) (model-free). The formal model-fitting approach simulating the thermal decomposition of solids by assuming a fixed mechanism was found to be unduly facile. However, activation energy (E) values calculated from two model-fitting techniques were considerably different from each other with a percentage difference in the range of 1.36% to 7.65%. Particularly, both model-fitting methods predicted different reaction mechanism for thermal disintegration of lignocellulosic materials (two-dimensional diffusion (D2) by Arrhenius and one-dimensional diffusion (D1) by Coat–Redfern method). Conversely, the model-free routine offers a transformation of mechanism and activation energy values throughout reaction and is, therefore, more authentic to illustrate the complexity of thermal disintegration of lignocellulosic particles. Based on the model-free kinetic analysis, the lignocellulosic materials may be devised in following order of activation energy: rice husk > bagasse > wheat straw, by both KAS and FWO methods with a percentage difference no more than 0.84% for fractional conversion up to 0.7. Isoconversional approach could be recommended as more realistic and precise for modeling non-isothermal kinetics of lignocellulosic residues compared to model-fitting approach.

Kinetic Analysis for the Catalytic Pyrolysis of Wood Plastic Composite Over Al-MCM-41.

This study examined the catalytic effects of Al-MCM-41 on the pyrolysis of wood plastic composite via the thermogravimetric analysis (TGA) and model-free kinetic analysis. Al-MCM-41 containing nanopores, with a high BET surface area (633 m²/g) and acidity (SiO₂/Al₂O₃:25), reduced the decomposition temperature of wood and plastic mixtures (PE and PP) in a wood-plastic composite. The average activation energy for the catalytic pyrolysis of wood plastic composite, which was calculated via a model-free kinetic analysis method (Ozawa) of TGA, was also lower at all conversions than those of non-catalytic pyrolysis. This suggests that the pores of Al-MCM-41 and its high cracking efficiency allow the effective diffusion of wood plastic composite components.

Determining Preexponential Factor in Model-Free Kinetic Methods: How and Why?

The kinetics of thermally stimulated processes in the condensed phase is commonly analyzed by model-free techniques such as isoconversional methods. Oftentimes, this type of analysis is unjustifiably limited to probing the activation energy alone, whereas the preexponential factor remains unexplored. This article calls attention to the importance of determining the preexponential factor as an integral part of model-free kinetic analysis. The use of the compensation effect provides an efficient way of evaluating the preexponential factor for both single- and multi-step kinetics. Many effects observed experimentally as the reaction temperature shifts usually involve changes in both activation energy and preexponential factor and, thus, are better understood by combining both parameters into the rate constant. A technique for establishing the temperature dependence of the rate constant by utilizing the isoconversional values of the activation energy and preexponential factor is explained. It is stressed that that the experimental effects that involve changes in the preexponential factor can be traced to the activation entropy changes that may help in obtaining deeper insights into the process kinetics. The arguments are illustrated by experimental examples.

Thermal Decontamination of Spent Activated Carbon Contaminated with Radiocarbon and Tritium

The thermal desorption of tritium (3H, T) and radiocarbon (14C) from spent activated carbon was investigated and three thermal desorption steps were established: the vaporization of homogeneously condensed molecules, the desorption of molecules physically binding with the carbon surface, and the decomposition of chemisorbed molecules. A model-free kinetic analysis was conducted to establish the optimum condition of vacuum thermal desorption. Physisorbed species, including tritiated water (HTO) and 14CO2, were effectively removed by vacuum thermal desorption. However, a fraction of 14C, which may take the form of carbon molecules in pyrocarbon form during the heating process, was not removed, even at a high temperature of 1000 °C under a vacuum of 0.3–0.5 Pa. Oxidative peeling of the pore surfaces by filling the evacuated pores with pure oxygen via vacuum thermal desorption and heating to 700 °C was found to be effective for reducing the level of 14C to a level below the established free-release criterion (1 Bq/g) when treating spent activated carbon with 14C radioactivity levels of 162 and 128 Bq/g. The reactivation of the spent granular activated carbon (GAC) by vacuum thermal desorption followed by surface oxidation was also confirmed by the slightly enhanced pore volumes when compared to those of virgin spent activated carbon.

Kinetic analysis and catalytic pyrolysis of spent medicinal herb over HZSM-5 and HY

In this study, the kinetic analysis on the pyrolysis of a spent medicinal herb, namely spent Achyranthes root, is performed using a thermogravimetric analyzer and a model-free kinetic analysis method, allowing the calculation of activation energy values without the assumption of kinetic model. Owing to the structural change of lignin and elimination of hemicellulose during the decoction of raw Achyranthes root, the thermogravimetric analysis results show a large difference between the derivative thermogravimetry curves of spent and raw Achyranthes roots. The average apparent activation energy value of spent Achyranthes root, obtained from the non-isothermal thermogravimetric analysis, are found to be lower than those of raw Achyranthes root. This comes as a result of the much lower content of hemicellulose in spent Achyranthes root caused by the hemicellulose elimination from raw Achyranthes root during the decoction process. The catalytic fast pyrolysis of spent Achyranthes root over HZSM5-30 (HZSM-5 with SiO2/Al2O3 = 30) and HY30 (HY with SiO2/Al2O3 = 30) was performed using a two-stage fixed-bed reactor system. The catalytic fast pyrolysis of spent Achyranthes root over both HY30 and HZSM5-30 produced the much larger amount of aromatic hydrocarbons, compared to the non-catalytic fast pyrolysis, with a parallel decrease of oxygen-containing pyrolyzates. Owing to its robust pore structure and high acidity, it was the HZSM5-30 that produced the highest quality oil during the catalytic fast pyrolysis of spent Achyranthes root, having higher selectivity of mono-aromatic hydrocarbons compared to HY30.

The Application of Model-free Kinetic Analysis to Thermal Stability Evaluation.

The Application of Model-free Kinetic Analysis to Thermal Stability Evaluation.

RAFT mediated miniemulsion copolymerization of ethylene and BMA and their non-isothermal model-free kinetic analysis

Miniemulsion copolymerization of ethylene and butyl methacrylate (BMA) was carried out at 60 °C using 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid as the reversible addition fragmentation chain transfer (RAFT) agent, sodium dodecyl sulphate as emulsifier and potassium per sulphate as free radical initiator under extremely low ethylene feed pressure of 5–20 bar. In the absence of a co-stabilizer, very stable emulsion was obtained, wherein the RAFT agent acted both as the chain transfer agent and as the co-stabilizer. FT-IR as well as NMR analysis established the formation of poly(ethylene-co-BMA) copolymer nanoparticles. The SEM analysis was used to study the morphological behaviour of poly(ethylene-co-BMA) copolymer nanoparticles. DLS analysis confirmed that the particle diameter Zavg of copolymer nanoparticles is in the range 100–140 nm and confirmed miniemulsion polymerization. In order to establish the stability of copolymers against thermal degradation, the kinetics and mechanism of thermal degradation of copolymers were investigated by thermogravimetric analysis. Thermogravimertic analysis established that thermal decomposition of poly(ethylene-co-BMA) copolymer nanoparticles occurred in the range 250–450 °C. This range is lower than the decomposition temperature of neat polyethylene (350–580 °C). Kinetic parameters were determined according to the model-free approaches of Friedman and Flynn–Wall–Ozawa. The multivariate nonlinear regression analysis was performed to determine the kinetic model and the corresponding kinetic triplets.

Кинетический анализ газофазного переноса кремния сульфидом цинка

The article gives a theoretical and experimental substantiation of the possibility of vapor transfer of silicon by a sulfide carrier—zinc sulfide. It is shown that, in terms of thermodynamics, the high-temperature interaction of Si with ZnS has all the signs of a chemical transport reaction and occurs at sublimation temperatures of zinc sulfide—above 1330 K. According to thermogravimetry (TG) data processed by the Ozawa–Flynn–Wall and ASTM methods of model-free kinetic analysis, the transfer of silicon in the form of volatile monosulfide can be considered with an acceptable approximation as a one-step reaction with average values of Eα and logA equal to 243.8 kJ/mol and 7.13 s–1, respectively. The temperature dependences calculated by the autocatalysis and solid nucleation models correlate well with experimental data of thermal analysis and do not contradict the proposed mechanism of sequential transformation Si → SiS2 → SiS (gas), where the rate of formation of silicon disulfide plays a decisive role. The HSC 6.1 Chemistry (Outotec) program and the Netzsch Thermokinetics software package were used in thermodynamic calculations and for kinetic analysis, respectively. The obtained information will find application in the development of a new halogen-free method for producing of high-purity silicon.

A comparative applicability study of model-fitting and model-free kinetic analysis approaches to non-isothermal pyrolysis of coal and agricultural residues

Comparative applicability of model-fitting and model-free kinetic methods to pyrolysis of two coals and four agricultural residues was analyzed by using two models from each class of methods. The two model-fitting methods were Arrhenius and Coats-Redfern while Friedman and Vyazovkin were selected from the model-free category. According to kinetic analysis by all four models, the fuels could be arranged in following order of activation energy, CC > DC > SD > RH > FS > CH. The two model-fitting methods exhibited different kinetic parameters (E and reaction mechanism). All fuels were found to have a third order reaction mechanism (F3) by using Arrhenius model. In the case of Coats-Redfern model, the CC and RH displayed 3-dimensional diffusion mechanism (D3) whereas CH, SD and FS exhibited third order reaction mechanism (F3). DC was found to decompose according to 2-dimensional diffusion mechanism (D2). The percentage difference between the values of activation energy found from the Arrhenius and Coats-Redfern models was in the range of 6.24–21.64%. The percentage difference between the values of activation energy from two isoconversional models was not more than 3.29% for coals and 4.91% for agricultural residues in the fractional conversion range of 0.1–0.7. Isoconversional models were found to be more reliable and accurate for estimation of non-isothermal kinetics for pyrolysis of solid fuels compared with model-fitting methods.

A thermogravimetric study of thermal dehydration of copper hexacyanoferrate by means of model-free kinetic analysis

The kinetics of thermal dehydration of K2x/3Cu[Fe(CN)6]2/3·nH2O was studied using thermogravimetry for x = 0.0 and 1.0. Data from both non-isothermal and isothermal measurements were used for model-free kinetic analysis by the Friedman and KAS methods. The water content was determined to be n = 2.9–3.9, plus an additional ~10% of water, likely surface adsorbed, that leaves very fast when samples are exposed to a dry atmosphere. The determined average activation energy for 0.2 ≤ α ≤ 0.8 is 56 kJ mol−1. The dehydration is adequately described as a diffusion-controlled single-step reaction following the D3 Jander model. The determined dehydration enthalpy is 11 kJ (mol H2O)−1 for x = 0.0 and 27 kJ (mol H2O)−1 for x = 1.0, relative to that of water. The increase with increasing x is evidence that the H2O molecules form bonds to the incorporated K+ ions.

Thermal decomposition and kinetics of residual rubber seed cake and shell

Solid wastes generated during biodiesel production process can be utilized to produce liquid fuel and biochar. Physicochemical properties and non-isothermal decomposition kinetics of rubber seed cake (RSC) and rubber seed shell (RSS) were investigated through proximate analysis, ultimate analysis and thermogravimetric analysis (TG). The TG experiments were conducted in the range of 30–800 °C under nitrogen atmosphere at heating rates of 2, 5 and 10 °C min−1. Active pyrolysis zones of RSC and RSS were broadly observed in three and two stages, respectively. The entire thermal decomposition of RSC (175–589 °C) occurred in wider temperature window compared to RSS (265.2–530 °C). The residual mass and ash content were higher in RSC sample. Model-free kinetic analysis of TG data was performed using various methods. The single value of activation energy obtained by the IKP method was found to be in good agreement with the average values of isoconversional methods. The calorific value of the RSC was found to be slightly higher than that of RSS. The current investigation suggests that both RSC and RSS can be used as feedstock materials for bio-oil and biochar production through pyrolysis process.

New approach for the kinetic analysis of cellulose using EGA-MS

This paper describes a new approach for kinetic analysis based on evolved gas analysis-mass spectrometry (EGA-MS) using pyrolyzer-gas chromatography/MS (Py-GC/MS). The kinetic results derived by this model-free kinetic analysis using the EGA-MS thermograms of cellulose were comparable to those using thermogravimetric analysis (TGA). The activation energies were in the range of 149–194 kJ/mol (mean 169 kJ/mol) for EGA/MS and 152–181 kJ/mol (mean 165 kJ/mol) for TGA. This suggests that Py-GC/MS can be used not only for the qualitative analysis of pyrolyzates, but also for the kinetic analysis of pyrolysis.

The influence of iron oxide on the oxidation kinetics of synthetic char derived from thermogravimetric analysis and fixed-bed experiments under isothermal and temperature-programmed conditions

The catalytic effect of iron oxide on the oxidation kinetics of synthetic char was investigated in a fixed-bed reactor and in a conventional thermobalance for comparison. Synthetic char doped with iron oxide was obtained by pyrolyzing hydrochar at 800°C, which had been synthesized by hydrothermal carbonization of cellulose in the presence of iron oxide. Isothermal char oxidation in the fixed-bed reactor resulted in the most reliable kinetic results. According to model-free kinetic analysis of these experiments at 15% conversion, iron oxide decreased the activation energy of char oxidation from 149kJ/mol to 133kJ/mol. Modeling of the conversion-time curves was first performed by using the uniform reaction model and then improved by using a n-th order power law. In the temperature range of 440–490°C a very good agreement with the experimental data was achieved using n=0.6. Activation energies amounting to 149kJ/mol and 134kJ/mol were derived for the undoped and iron oxide-doped char, respectively, well in line with the model-free analysis.

Novel cardanol-containing boron-modified phenolic resin composites

To improve the thermal stability of phenolic resin and develop functional sustainable adhesive, a thermal-resistant cardanol-containing boron–phenolic resin (CBPR) was prepared by copolymerizing salicyl alcohol, cardanol, and boric acid. The structure of CBPR was characterized by Fourier transform infrared spectroscopy. Thermal stability of the investigated composites was estimated using thermogravimetric analysis (TGA). The results of TGA indicated that the modified resin exhibited excellent thermal stability. Specifically, the B-0.2 thermoset had a char yield of 69% when the boron content was only 1.27 wt%. The curing kinetic behavior was well described by differential scanning calorimetry and model-free kinetic analysis. Further, CBPRs, nano-aluminum oxide powders, glass powders with low melting point, and vitreous silica fibers were used as resin matrix, filler, forming additive, and reinforced material, respectively, to produce a novel ceramizable phenolic molding composite. The ablative characteristics of the co-cured blends were explored in terms of linear/mass ablation rate and microscopic pattern of ablation via the oxyacetylene torch tests. After thermal treatment, the formation and growth of the ceramic phase enhanced the thermal stability and ablation performance of the composites at high-temperature region. The morphology and phase composition of the residual chars were studied by scanning electron microscopy and energy dispersive spectroscopy, respectively. The linear and mass ablation rates for the modified composites decreased obviously in comparison with those of the unmodified composites, indicating that the modified composites possessed enhanced thermal stability and ablation property.