Sestak Berggren Model Research Articles

Experimental and numerical investigation of chemical-loop steam methane reforming on monolithic BaCoO3/CeO2 oxygen

Chemical looping steam methane reforming (CL-SMR) is a promising approach to co-production of syngas and hydrogen. As the CL-SMR process relies on the redox reaction of the oxygen carriers, the reactivity of oxygen carriers is crucial in the performance of CL-SMR. In this study, a monolithic BaCoO3/CeO2 oxygen carrier was synthesized, and the reaction performance was evaluated in CL-SMR. The kinetic parameters were determined based on Sestak-Berggren model, an unsteady-state CFD model was established to predict the dynamic reaction processes in three reaction stages of CL-SMR. The result suggests that the flow rate of inlet gas in reaction stages could affect the mass transfer during gas-solid reactions, and then change the evolution and distribution of reaction rate in monolithic oxygen carrier. Increasing the flow rate could improve the uniformity of reaction rate distribution and decrease the time consumption for cyclic process, but decreased the concentration of gas productions and increased the burden of gas product separation at the same time. Among three reaction stages, the conversion of oxygen carrier was accelerated with the increase of temperature, and the varied half-life time of conversions suggested that the reactivity in RS stage is intense and the reactivity in AC stage is mild.

Comprehensive Understanding of the Heavy Oil Combustion Process: Reaction Behavior, Kinetic Triplet, and Mechanism Implication.

In this work, thermo-oxidative behavior, kinetic triplet, and free radical mechanism of ultraheavy oil during an in situ combustion (ISC) process were systematically surveyed via multiple thermal analysis techniques (TG/DTG/DSC/PDSC), model-free methods, and related mathematical simulation. First, specific mass loss, exothermic intensity, and corresponding temperature intervals were respectively determined in low-/high-temperature oxidation (LTO/HTO) regions. In addition, the comparison of atmospheric/pressurized differential scanning calorimetry (DSC/PDSC) experiments indicated that the pressurized conditions could obviously strengthen the oxidation progress with more heat emission. Then two model-free methods were contrastively employed for PDSC data to calculate LTO and HTO activation energy variations with the conversion rate. Moreover, the acceleratory rate model for LTO and the Sestak-Berggren model for HTO were accordingly picked as the most probable mechanism functions, which were later used to determine the simulated curves. Then, the simulations of α-T and dα/dT-T curves were respectively attained using Friedman equation in MATLAB software and contrasted with experimental data to validate the accuracy of the yielded kinetic triplet and forecast the combustion behavior. Further, the evolution pathways of the underlying oxidation mechanism was illustrated. This study updates the understanding of the nonisothermal combustion process, contributing to the subsequent numerical simulation and feasible investigation for in situ combustion implementation to enhance heavy oil recovery.

Non-isothermal decomposition kinetics of commercial polyacrylamide hydrogel using TGA and DSC techniques

The thermal decomposition method was employed to analysis the non-isothermal kinetics of commercial polyacrylamide hydrogel. Malek model-based methods and Vyazovkin model-free advanced converter methods were used to analyze the non-isothermal kinetics of hydrogel decomposition using DSC and TGA data. Thermal decomposition takes place in two stages. FTIR diagrams showed that ammonia gas and CO2 were likely released during the first and second stages of decomposition, respectively. By breaking the main chain in the second stage, the polymer loses a significant amount of weight. The Sestak-Berggren model describes the reaction process. The activation energies for the first and second stages were calculated to be (40±3 kJ/mol) and (59±3 kJ/mol), respectively. Finally, a commercial polyacrylamide hydrogel decomposition explicit rate equation was derived. The increase in surface porosity with the progress of the degradation process can be evidence of autocatalysis effects.

Crystallization kinetics analysis of Ge18BixSe82-x chalcogenide glasses alloys by using non-isothermal methods

The melt quench method is used to prepare the chalcogenide glass Ge18BixSe82-x (x: 0.5, 2, 4, 6, and 8 at percent). The samples are characterized using X-ray diffraction (XRD) and a scan electron microscope (SEM). The kinetics of crystallization of the chalcogenide glasses under consideration are investigated by using Differential Thermal Analysis (DTA) under non-isothermal conditions. Different models are used to calculate the activation energy of crystallization (Ec). The Kissenger-Akahira-Sunose (KAS) method is used to calculate the change of activation energy with crystallization volume fraction (Ecα). As well, the activation energy of glass transitions is measured by using different models. The results of fitting the experimental DTA data to the computed DTA curves show that the Johnson-Mehl-Avrami (JMA) model cannot represent the crystallization process of Ge18BixSe82-x glass. Our findings show that the Sestak-Berggren (SB) model is better suited to describe the crystallization process for the glass under investigation.

Co-pyrolysis of waste tyre and pine bark: Study of reaction kinetics and mechanisms

Thermal processing of waste tyre and biomass through pyrolysis and gasification provides a promising pathway to address issues raised by anthropogenic activities including energy security, waste management and environmental sustainability. The study of the kinetics underlying the decomposition of the waste tyre and biomass blend through pyrolysis is an essential step to understand their further reactions in the reforming/cracking stage and to optimize their use. Kinetics analysis of the thermal decomposition of the waste tyre and pine bark with mass blend ratios of 1:0, 3:1, 1:1, 1:3 and 0:1 was investigated using thermogravimetric analysis. Results indicated that the change in heating rates from 10 to 40 K/min with an increment of 10 K/min caused a shift in differential thermogravimetry curves of all the samples to a higher temperature. To evaluate the possible interaction between waste tyre and pine bark in the blended samples, the difference in the weight loss (Δw) was calculated. Occurrence of positive synergetic interaction in terms of increased weight loss between waste tyre and pine bark at different blend ratios varied with the variation in heating rate. Activation energy and pre-exponential factor for different blend ratios were calculated using model fitting method (i.e. Coats-Redfern) and iso-conversional methods (i.e. FWO, KAS and Friedman) as well as combined kinetic analysis. Based on iso-conversional methods and combined kinetic analysis, the single waste tyre has higher activation energy than the single pine bark sample. However, waste tyre and pine bark blend samples with mass ratios of 3:1, 1:1 and 1:3 showed lower activation energy than waste tyre, signifying the benefits of using pine bark in blend samples. The maximum synergetic interaction in terms of lowest activation energy was reported with the use of the waste tyre and pine bark with a mass blend ratio of 3:1. The reaction mechanisms of WT1PB0, WT3PB1, WT1PB1, WT1PB3 and WT0PB1 were evaluated using the Sestak Berggren model and as follows; α−1.866(1−α)1.000[−ln(1−α)]−2.276, α−1.171(1−α)1.000[−ln(1−α)]−3.007, α1.765(1−α)1.000[−ln(1−α)]−5.381, α−2.324(1−α)2.913[−ln(1−α)]−1.272 and α−7.735(1−α)5.658[−ln(1−α)]5.594, respectively. The results of the current study will contribute to the knowledge of expanding waste disposal options and provide essential information for the development of an energy sustainable system.

Understanding the reaction kinetics of diesel exhaust soot during oxidation process

The purpose of the present study is to better understand the reaction kinetics of diesel exhaust soot during oxidation process. A thermogravimetric analyzer was used to oxidize real diesel exhaust soot generated from a Euro VI diesel engine under non-isothermal conditions. The Friedman-Reich-Levi method and the Sestak-Berggren model were used to determine the oxidation kinetics. Raman spectroscopy and high-resolution transmission electron microscopy were employed to follow the changes of the soot structure during oxidation. The activation energy gradually increased with increasing conversion level during soot oxidation. The oxidation process of diesel exhaust soot could be described as three-step kinetics, and the calculated conversions fitted the experimental results very well. The kinetic predictions of diesel soot oxidation that were obtained using the proposed kinetic models were more accurate and precise than those with the common first-order model. The structural order increased as oxidation progressed, which was responsible for the increased activation energy. The structural ordering was principally caused by the preferential oxidation of the disordered fraction in the diesel soot, especially for the amorphous carbon, which was oxidized in the initial stage of the oxidation reaction.

Investigation of the processability, thermal, mechanical and flame retardant properties of bisoxazoline composites

Presented here is an investigation into the cure kinetics, thermal and mechanical properties, and fire resistance of a carbon fibre composite using a polymer matrix blend composed of 1,3 phenylene bisoxazoline, a phenolic resin and dodecylbenzene sulfonic acid . This polymer matrix is further modified with a benzoxazine, a tetra-functional epoxy amine resin and the engineering thermoplastic , polyether sulfone (PES) to explore their effect on the reaction mechanism and final properties of the composite after cure and post-cure. The modifiers reduce the reactivity of polymerisation and the final glass transition temperature of the network as shown by the rate constants, determined from the Kissinger and Sestak–Berggren models. Subsequent post-curing of the composite increases the glass transition temperature, thermal stability, interlaminar shear strength , and fire performance as determined by UL-94 vertical burn test. Ensuring the network is fully cured is clearly critical to optimum performance of the composite. The high char yields of the bisoxazoline polymer networks , particularly after post-cure illustrate great potential for applications where high temperature resistance is required.

High-Temperature Stability and Pyrolysis Kinetics and Mechanism of Bio-Based and Petro-Based Resins Using TG–FTIR/MS

Pyrolysis behavior of resins is essential for their high-temperature application. Herein, the high-temperature stability and pyrolysis kinetics and mechanism of rosin glyceride (RGE), hydrogenated rosin glyceride (HRGE), C9 petro-based resin (C9PR), and hydrogenated C9 petro-based resin (HC9PR) under a nonoxidizing atmosphere were investigated by thermogravimetry coupled with Fourier transform infrared spectrometry or mass spectrometry (TG–FTIR/MS) techniques. Friedman and Starink methods as well as reaction-order and truncated Sestak–Berggren models were used to evaluate kinetic and thermodynamic parameters, and results indicated that f(α) = (1 – α)n was the most probable pyrolysis mechanism for different resins. In addition, the average activation energies for pyrolysis of RGE, HRGE, C9PR, and HC9PR obtained by the Starink method were 188.97, 170.95, 159.69, and 151.66 kJ/mol, respectively, suggesting that bio-based resins exhibited better high-temperature stability than cycloaliphatic or aromatic petro-based resins thanks to their unique tricyclic phenanthrene structures, and the high-temperature stability of resins mildly would decrease after hydromodification due to the cracking of saturated bonds, which was well supported by TG–FTIR/MS analyses. Possible pyrolysis pathways were proposed.

Polymerization kinetics of adamantane-based dicyanate ester and thermal properties of resulting polymer

The kinetics of liquid-state polymerization of adamantane-based dicyanate ester has been studied for the first time by means of conventional and temperature-modulated DSC. It has been detected that the later stages of polymerization undergo a transition from kinetic- to diffusion-controlled regime. Detailed analysis of the polymerization kinetics in the reaction-controlled regime has revealed that the process rate can be well described in the frameworks of the presently proposed autocatalytic quasi-one-step model. The proposed model eliminates arbitrarily guessing the value for the initial conversion that provides a reasonable alternative to the broadly used truncated Sestak-Berggren model. The adamantane-based dicyanate ester polymerization product demonstrates markedly higher thermal stability and glass transition temperature compared to those of dicyanate esters with flexible hydrocarbon bridging units. The obtained experimental results confirm our hypothesis about the influence of the rigidity of cyanate ester molecule on its reactivity and thermal properties of the corresponding polymer product.

Thermal Behavior, Reaction Pathways and Kinetic Implications of Using a Ni/SiO2 Catalyst for Waste Tire Pyrolysis

Catalytic pyrolysis has been used to upgrading the quality of pyrolytic liquids. Herein, we report a comprehensive study on the catalytic pyrolysis of waste tires using Ni/SiO2 as catalysts. The analyses were carried out by combining thermogravimetry (TGA), TGA interfaced to a Fourier transform infrared spectrometer (TGA–FTIR), and pyrolysis coupled to gas chromatography/mass spectrometer (Py–GC/MS) techniques. During waste tire decomposition, the main functional groups detected in the FTIR were alkenes, aromatics, and heteroatoms-containing groups such as nitrogen, sulfur, and oxygen. Meanwhile, by Py–GC/MS were identified mainly D,L-limonene, isoprene, benzene, toluene, xylenes (BTX), and p-cymene. The Py–GC/MS experiments at three different temperatures (350, 400, and 450 °C) suggested an effect of the catalyst on product distribution. The Ni catalyst promoted cyclization reactions and subsequently aromatization, leading to an improved vapors composition. The use of iso-conversional kinetic models along with master plots allows proposing a multiple-step reaction mechanism, which was well described by the Avrami–Erofeev, Random Scission, and truncated Sestak–Berggren models. The values of activation energies show differences for the catalyzed and uncatalyzed pyrolysis (111.0 kJ mol−1 and 168.4 kJ mol−1), validating the effectivity of Ni/SiO2. Finally, the thermal Biot (> 1) and PyI and PyII numbers (10–3 < PyI < 10–1 and 10–2 < PyII < 10–3) confirms that the process is being occurred between the kinetic and the convection-limited regimes.Graphic Abstract

Ex-solution kinetics of nickel-ceria–doped strontium titanate perovskites

Nickel ex-solution from La0.3Sr0.5NixTi1-xO3-δ (LSNxTA-) perovskites containing different nickel fractions (x = 0.04 and 0.16) is studied using temperature-programmed reduction (TPR) and chemisorption. Non-isothermal reduction of nickel occurs through two steps as confirmed using two-parameter Sestak-Berggren model, where the nuclei of nickel are formed at low temperatures, which grow through at elevated temperatures. The kinetic triplets (Ea, f(α), and ln A) are estimated from the Sestak-Berggren model. The nucleation at elevated temperature is the rate-determining step whose activation energy (Ea) is reduced with higher nickel loadings in the perovskite. Doping ceria at the A-site in LC0.04SN0.16TA- increases the dispersion of nickel, estimated using chemisorption studies in comparison to LSN0.16TA- perovskites. Physical characterization of sthe reduced perovskites using X-ray photo electron spectroscopy is used to correlate the ex-solution process with the Sestak-Berggren model.

Extensive thermal study of sulfur dopants effects on the selenium tellurium glasses

Initially, Sulfur (S) doping in Se90Te10 glassy alloy was utilized for clarifying the effects produced by minerals on its glass mesh and kinetic characteristics. The crystallization kinetics of bulk Se90Te10 and (Se90Te10)95S5 with different heating rates were analyzed by the differential scanning calorimetry. The processes of the alloy recrystallization after the thermal treatment were recognized by X-ray diffraction. The activation of energy, Eg, of glass transition crystallization, Ec, was utilized for determining various kinetic models. The analysis and experimental data revealed that Eg and EC differ for the additive elements. The effective Ec of crystallization was calculated based on the Kissinger formula. Thus, the Sestak–Berggren model was used for characterizing the DSC crystallization information when it agreed to the experimental results. Consequently, it was found that the Johnson–Mehl–Avrami model can be applied at high heating rates.

Kinetic modelling of thermal processes using a modified Sestak-Berggren equation

This study outlines the principles of modelling the kinetics of solid-state reactions through the simultaneous fitting of multiple peak curves using the modified Sestak-Berggren equation. This mathematical model gives an indication of the mechanism occurring and allows kinetic parameters, such as activation energy, to be estimated. This methodology is demonstrated using in silico thermo-conductivity detector (TCD) data showing the internal consistency of the Sestak-Berggren modelling approach, its applicability to noisy data and its ability to predict mechanisms occurring during a thermally induced solid state reaction. Using these in silico data it has been confirmed that this empirical model can separate overlapped peaks without a priori peak deconvolution. A rigorous statistical methodology based on the Akaike Information Criteria, is recommended to identify the optimum number of thermal events that should be applied to a system. This modified Sestak-Berggren model is then applied to an experimental dataset of temperature programmed reduction of a calcined cobalt on alumina catalyst precursor. This allows for the identification of a statistically adequate kinetic triplet for each thermal event. Recommendations on the treatment of datasets which contain “shoulders” and closely overlapped peaks are also given.

Investigating Waste Plastic Pyrolysis Kinetic Parameters by Genetic Algorithm Coupled with Thermogravimetric Analysis

Pyrolysis of waste plastic (WP) is a promising method to solve the plastic pollution issue. WP is mainly composed of polyethylene (PE). Moreover, the products of waste polyethylene (WPE) pyrolysis could serve as high quality fuels and the feedstocks of petrochemicals. Therefore, it is essential to investigate the WPE and WP pyrolysis process. This study evaluates pure PE, WPE and WP pyrolysis kinetic parameters by the use of genetic algorithm (GA) and isoconversional methods coupled with thermogravimetric analysis (TGA), respectively. Additionally, three representative reaction models, i.e. reaction-order, extended Prout–Tompkins and Sestak–Berggren models, are investigated for obtaining the most suitable model, which could describe the PE, WPE and WP pyrolysis process more accurately. Consequently, the reaction-order model turns out to be the optimal method for appropriately describing PE, WPE and WP pyrolysis processes. Hence, the pyrolysis parameters optimized by GA are proven to be accurate and reliable, in comparison of calculated values of activation energy by isoconversional methods and experimental data. Moreover, it might be applicable of GA coupled with TGA with reaction-order model to the future industrial WPE and WP pyrolysis circumstances that have variable heating rates.

Non-isothermal nanocrystallization of Fe83.3Si4B8P4Cu0.7 (NANOMET®) alloy: modeling and the heating rate effect on magnetic properties

The kinetics of the nanocrystallization of a Fe83.3Si4B8P4Cu0.7 amorphous alloy by using differential scanning calorimetry has been investigated by non-isothermal annealing in a wide heating rate range from 10 °C min−1 to 200 °C min−1. The amorphous alloy was prepared by melt-spinning and showed a two-stage crystallization. In the first crystallization stage, α-Fe nanocrystals are formed. This phase is responsible for the good soft magnetic properties. The activation energy during the crystallization of the α-Fe nanocrystalline phase was determined from an isoconversional approach, and was found to be distinctively varying during the crystallization. An attempt was made to model the crystallization in an interval where the activation energy is relatively constant. The Malek criterion indicated that the Kolmogorov–Johnson–Mehl–Avrami model is not appropriate, whereas the Sestak–Berggren model meets the criterion. The acquired model shows good agreement with the experimental results. The magnetic properties of annealed ribbons at different heating rates show an initially steep decrease of the coercivity (Hc) from 82 A m−1 at a heating rate of 10 °C min−1 to 20 A m−1 above 100 °C min−1, whereas saturation magnetization (Ms) is practically invariant at ca 175 Am2 kg−1. This dependence is explained as due to diminishing grain size with higher heating rates, which is further supported by x-ray diffraction measurements.

Morphology, structure and thermal analysis of (As50Se50)100−xAgx glasses

The structural and crystallization kinetics of (As50Se50)100−xAgx (x = 0, 5, 10 and 15 at.%) glasses are reported. The glass transition activation energy, Et, decreased from 185.19 to 179.94 eV with increasing the Ag content. The crystalline phases AsSe, AgAsSe2 and Ag2Se phases were found in the annealed glasses. The structure of the annealed samples at different temperatures was examined using scanning electron microscopy. The crystallization kinetics parameters were calculated using the iso-conversional models. A slight increase in Ec(χ) from with the conversion (χ), which accounts for single-step mechanism, was found. The results of the conversion dependence of the Avrami exponent n(χ) showed an increase from 1.22 to 1.31 with the Ag content and conversion (χ) as well. The average values of n(χ) are accounted for two- and three-dimensional crystal growth with heterogeneous nucleation. Comparing the experimental DSC data with calculated ones indicated that Sestak–Berggren model was found to be suitable for describing the crystallization process of the investigated chalcogenide glasses.

Effect of Gaseous Products on the Kinetics of Thermal Decomposition of Chloride-Containing Complex Ammonium Nitrate-Based Fertilizers

The results of studying the effect of gaseous products on the kinetics of thermal decomposition of chloride-containing complex ammonium nitrate-based fertilizers using the methods of thermogravimetry and differential scanning calorimetry are presented. The experimental data were analyzed with the Sestak–Berggren model fitting method and the isoconversion differential Friedman method. Based on the results of the studies, the dependences of the decomposition rate on the degree of decomposition are determined and a conclusion is drawn on the reasons of the influence of the self-generated atmosphere on the kinetics of exothermic decomposition.

Thermal Decomposition Reaction Kinetics of Hematite Ore

In order to understand the thermal decomposition kinetics of hematite particles in inert atmosphere, thermogravimetriy was employed for isoconversional analysis. The kinetic triplet was estimated from the experimental data and the isothermal reaction kinetics was predicted. The results indicated that the thermal decomposition could be divided into two stages, of which the activation energies were 636 kJ/mol and 325 kJ/mol, respectively. The exponential form of pre-exponential factor, ln(A/s−1), for the two stages were estimated to be 42.9±6.6 and 14.1±3.08. At last, the kinetic mechanism of the first stage was suggested to match Sestak-Berggren model as f(α)=(1−α)1.38. The relatively slow reaction rate of the second stage was due to the slag formation during the reaction.

A kinetic study and thermal decomposition characteristics of palm kernel shell using model-fitting and model-free methods

The thermal decomposition behaviours of palm kernel shells (PKS) under non-isothermal conditions were investigated using the thermogravimetric analyser. A comparison of model-free and model-fitting methods for PKS decomposition was performed. Differential and integral methods used showed an increase in apparent activation energy with the conversion. Besides that, the global single reaction mechanism was evaluated using the reaction order and Sestak-Berggren models. Curve fitting results showed that Sestak-Berggren’s model demonstrated that the PKS pyrolysis mechanism was better than the reaction order model. The components, namely moisture, hemicellulose, cellulose, and lignin were found to decompose simultaneously. From Kissinger’s method, the average activation energy for devolatilisation, cellulose, and hemicellulose were 24.65 kJ mol−1, 78.98 kJ mol−1, and 183.07 kJ mol−1 , respectively. The decomposition of lignin occurred slowly, with a slower conversion rate in contrast to the hemicellulose and cellulose components. Highlights PKS pyrolytic kinetics were studied through KAS, FWO and Friedman methods. Model-free methods can predict lignocellulosic biomass components activation energies well. The three independent-parallel-reaction model fits well with experimental data.

Glass transition and crystallization kinetics of a new chalcogenide-alkali metal $$\hbox {Se}_{80}\hbox {Te}_{8}(\hbox {NaCl})_{12}$$ Se 80 Te 8 ( NaCl ) 12 alloy

A new chalcogenide-alkali metal alloy of \(\hbox {Se}_{80}\hbox {Te}_{8}(\hbox {NaCl})_{12}\) has been prepared by a melt-quench technique. The crystallized phases due to the thermal annealing are observed by X-ray diffraction of the powdered sample. The glass transition and kinetics of crystallization in the \(\hbox {Se}_{80}\hbox {Te}_{8}(\hbox {NaCl})_{12}\) alloy are studied using the differential scanning calorimetric technique under non-isothermal conditions. The activation energy of the glass transition is evaluated by Kissinger and Mahadevan methods. The crystallization activation energy (\(E_{\mathrm{c}}\)) is calculated by isoconversion Friedman methods. The decrease of \(E_{\mathrm{c}}\) with increasing crystallization conversion is attributed to the complex mechanism of the crystallization process. Based on the shape of the characteristic kinetic function, the crystallization growth is found to be a three-dimensional growth from the bulk nuclei. The results show that the conditions of the Sestak–Berggren model are satisfied for describing the crystallization process of the studied \(\hbox {Se}_{80}\hbox {Te}_{8}(\hbox {NaCl})_{12}\) alloy. The parameters M and N involved in this model are calculated and related to the crystallization process.