Model-free Kinetic Methods Research Articles

Thermal Stability, Durability, and Service Life Estimation of Woven Flax-Carbon Hybrid Polyamide Biocomposites.

Woven flax-carbon hybrid polyamide biocomposites offer a blend of carbon fibers' mechanical strength and flax's environmental advantages, potentially developing material applications. This study investigated their thermal behavior, degradation kinetics, and durability to water uptake and relative humidity exposure and compared them with pure flax and carbon composites with the same matrix. The hybrid composite exhibited intermediate water/moisture absorption levels between pure flax and carbon composites, with 7.2% water absorption and 3.5% moisture absorption. It also displayed comparable thermal degradation resistance to the carbon composite, effectively maintaining its weight up to 300 °C. Further analysis revealed that the hybrid composite exhibited a decomposition energy of 268 kJ/mol, slightly lower than the carbon composite's value of 288.5 kJ/mol, indicating similar thermal stability. Isothermal lifetime estimation, employing the activation energy (Ed) and degree of conversion facilitated by the Model Free Kinetics method, indicated a 41% higher service life of the hybrid laminate at room temperature compared to the carbon laminate. These insights are crucial for understanding the industrial applications of these materials without compromising durability.

Estimating shelf life and degradation mechanisms of nitrile butadiene rubber for viscoelastic dampers

This study investigates the shelf life of nitrile butadiene rubber (NBR) based on age and temperature factors. Natural aging of nitrile butadiene rubber samples is performed under laboratory conditions for 2 years, followed by thermogravimetric analysis to evaluate Arrhenius parameters. Toop’s equation is used to predict shelf life at 5% conversion rate. Model-free kinetic methods, including Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS), and Kissinger, estimate shelf life at different temperatures for both virgin and naturally aged nitrile butadiene rubber. Results show close correlation between KAS and Kissinger methods, with slight variations in activation energy impacting shelf life. Fourier-transform infrared spectroscopy (FTIR) tests assess functional group changes with age. Virgin nitrile butadiene rubber activation energy: OFW-73.33 kJ/mol, KAS-68.43 kJ/mol. Aged nitrile butadiene rubber activation energy: OFW-72.57 kJ/mol, KAS-67.88 kJ/mol. Shelf life at 40°C: Virgin nitrile butadiene rubber - OFW-111.29 years, KAS-26.31 years. Aged nitrile butadiene rubber - OFW-89.01 years, KAS-22.37 years. These findings provide valuable insights for predicting and assessing nitrile butadiene rubber viscoelastic damper performance in engineering applications.

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.

Processability and reprocessability maps for vitrimers considering thermal degradation and thermal gradients

A lack of fundamental knowledge about the kinetic mechanisms governing the processing and reprocessing of vitrimers forces a trial-and-error procedure to be adopted when choosing treatment conditions. In this work, we develop diagrams to be used as a straightforward tool to decide the curing and thermoforming parameters of vitrimers. The thermal stability of a disulfide containing epoxy has been evaluated by means of thermal analysis methods. By characterizing the kinetics of the curing and decomposition of the resin through a model-free kinetic method, we have been able to generate an intuitive processability map based on Time-Temperature-Transformation plots. The resulting chart allows for the optimum curing conditions that will avoid degradation to be identified. A similar chart for reprocessability has been obtained by considering the exchange kinetics of the characteristic stress relaxation behavior of vitrimers. Furthermore, we have incorporated into the diagrams criteria to determine the critical thickness below which a tolerable thermal gradient is not exceeded. Our diagrams have been experimentally validated, thus proving to be a useful and valid tool for rapid decision-making situations.

Application of machine learning methods for lignocellulose biomass pyrolysis: Activation energy prediction from preliminary analysis and conversion degree

The investigations of biomass pyrolysis kinetics are traditionally accomplished through experiments at the expense of extensive resources worldwide. The estimation of activation energy (Eα) of biomass pyrolysis is a crucial and essential aspect of process optimization and control. In this study, machine learning methods were applied for the first time to predict the Eα values of the pyrolysis process based on the preliminary analysis of the biomass feedstocks and conversion degree (α). A total of 1523 sets of Eα values calculated via three frequently-used model-free kinetic methods were collected from literature and modeled by using artificial neural network (ANN), random forest (RF), and support vector machine (SVM) algorithms. The training and optimization of the models showed that the RF algorithm exhibited satisfactory accuracy, making it a promising tool for a quick prediction of Eα values. Moreover, the feature importance analysis indicated that Eα mainly depended on the α, C content, and ash content of the biomass. This work suggested the effective application of machine learning in determining Eα accurately, which could help in understanding the pyrolysis mechanisms, reducing the experimental workload, and improving the optimization of the pyrolysis process.

Thermal and mass spectrometer analysis (TG - DTG - MS) of different oAPI gravity crude oils from new oil fields in Turkey

In this research, thermal analysis and kinetics of four different crude oil samples (oAPI range of 21.1–34.1) from different new oil fields of Turkey were studied using thermogravimetry (TG-DTG) coupled with a quadruple mass spectrometer (MS). Mixtures of crude oils and limestone matrix are prepared to give a composition of 15 % wt. crude oil in the matrix and the ramped temperature experiments are performed at different heating rates (10, 20 and 30 °C/min) under air atmosphere. In TG-DTG analysis three different reaction regions were observed, known as low temperature oxidation (LTO), fuel deposition (FD), high temperature oxidation (HTO) and finally limestone decomposition, respectively. In MS analysis, combustion products of different crude oils on the basis of both relative intensities and relevancy was monitored simultaneously. Finally, two different model free kinetic methods known as Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS) were used to determine the activation energy of the crude oil samples. It was observed that the activation energy values are varied between 189.47 and 290.41 kJ/mol (OFW method) and 181.75–288.37 kJ/mol (KAS method) in HTO region, respectively.

Hydrothermal carbonization of cow dung with human urine as a solvent for hydrochar: An experimental and kinetic study

Hydrothermal carbonization (HTC) is the most cost-effective, environmentally friendly, and efficient physicochemical and biochemical process for converting biomass to products with added value. The objective and novelty of this work is to produce and investigate the qualities of hydrochar fuel (as a solid fuel) from cow manure using human urine as a solvent in order to find a suitable replacement for conventional fuel (i.e., coal). HTC based studies were conducted in batch, at three different reaction temperatures (180 °C, 200 °C, and 220 °C) and two different reaction periods (2 and 4 h). For kinetic analysis and reaction mechanism of the combustion behavior of the produced hydrochar, the model free kinetic methods and the z-master plot were used. From the model free kinetics methods, it was observed that the resultant optimum average activation energy and pre-exponential factor for the produced hydrochar at 180 °C and 2 h reaction period (HTC_180_2) were ∼120 kJ/mol and ∼5.59 × 1025 sec−1, respectively. In addition, the little variation between ΔEα and ΔHα (∼10 kJ/mol) suggests that the combustion of produced hydrochar (HTC_180_2) occurred with minimal energy use. Furthermore, the hydrochar exhibited its highest heating value at 200 °C for 4 h (HTC_200_4) which was 1.44 times higher than the raw dung (13.4 MJ/kg) due to the HTC process. The produced hydrochar demonstrated a significant improvement compared to the conventional solvent, i.e. water.

Detailed kinetic analysis and modelling of the dry gasification reaction of olive kernel and lignite coal chars

The dry gasification process of solid fuels is a promising pathway to mitigate and utilize captured CO2 emissions toward syngas generation with tailored composition for several downstream energy conversion and chemical production processes. In the present work, comprehensive kinetic analysis and reaction modelling studies were carried out for olive kernel and lignite coal chars gasification reaction using pure CO2 as gasifying agent. Chars reactivity and kinetics of the gasification reactions were thoroughly examined by thermogravimetric analysis at three different heating rates and correlated with their physicochemical properties. The reactivity of olive kernel char, as determined by the mean gasification reactivity and the comprehensive gasification characteristic index, S, was almost three times higher compared to that of the lignite coal char. It was disclosed that the fixed carbon content and alkali index (AI) have a major impact on the reactivity of chars. The activation energy, Ea, estimated by three different model-free kinetic methods was ranged between 140 and 170 kJ/mol and 250–350 kJ/mol for the olive kernel and lignite coal chars, respectively. The activation energy values for the lignite coal char significantly varied with carbon conversion degree, whereas this was not the case for olive kernel char, where the activation energy remained essentially unmodified throughout the whole carbon conversion range. Finally, the combined Malek and Coats-Rendfrem method was applied to unravel the mechanism of chars-CO2 gasification reaction. It was found that the olive kernel char-CO2 gasification can be described with a 2D-diffusion mechanism function (D2) whereas the lignite coal char-CO2 gasification follows a second order chemical reaction mechanism function (F2).

반응성 필러로써 Aluminum Fumarate을 이용한 Dicyanate Composites의 물성 강화: 열역학적 특성 연구

In this work, the synthesized nanoporous aluminum fumarate (Al_FA_A) metal organic framework (MOF) has been used as reactive filler for the bisphenol-A dicyanate (BADCy) resin system. The use of Al_FA_A is interesting due to the involvement of double bonds (fumarate) in triazine during polymerization. The thermal properties of the polymers formed with and without reactive filler were evaluated under different curing temperatures, prepolymerizations and post-polymerizations conditions. All the samples were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction analysis (XRD) and Evolved gas analysis. On the contrary, the cure chemistry was determined by non-isothermal model free kinetic methods. This study provides a new path to utilize the MOFs as reactive nanoparticle fillers to obtain multifunctional materials.

Cure mechanism and kinetic prediction of biobased glass/polyfurfuryl alcohol prepreg by model-free kinetics

This paper explains the cure reaction mechanisms of a novel bio-based glass/Polyfurfuryl prepreg using an experimental and numerical approach. It suggests optimized parameters of rapid curing for isothermal curing conditions. Dynamic scanning calorimetry (DSC) under non-isothermal conditions was used to determine parameters for the two model-free kinetic methods Friedman and Ozawa Flynn Wall. The average activation energy (88.9 ± 4.9 kJ/mol) was found to be higher than that reported for neat resin in literature. The validated models were used to gain insight into reaction mechanisms and were used to predict the evolution of reaction time under isothermal conditions for the PFA prepreg. This suggested that the curing time can be reduced to half by rapidly heating and maintaining isothermal conditions at 160°C, which provides faster curing using hot-press. In addition, dynamic mechanical analysis (DMA) was carried out to compare the manufacturer recommended cure cycle with the rapid cycle suggested.

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.

Kavun çekirdeği pirolizine ait kinetik parametrelerin ve termodinamik özelliklerin belirlenmesi

The aim of this study is to examine the behaviour of melon seed pyrolysis and to calculate its kinetic parameters along with thermodynamic properties. The thermogravimetric analysis experiments were conducted from ambient temperature to 800°C under nitrogen atmosphere at the heating rates of 5, 10, 20 and 40°C/min. It was determined that the pyrolysis process underwent through four stages where the second and third stages were the active pyrolysis stages. Kinetic calculations were carried out using model-free Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Starink and model-based Coats-Redfern methods. The apparent activation energy values of the second and third stages were calculated to be in the ranges of 123.9–215.5 and 141.9– 234.2 kJ/mol, respectively. The Coats-Redfern method demonstrated that the second and third stages fit the reaction mechanisms of F1.65 and D5, respectively. Moreover, the enthalpy, entropy and Gibbs energy changes of the active pyrolysis stages performed at 10°C/min heating rate were determined using the results calculated from the model-free kinetic methods. The results obtained in the present study will be useful to provide necessary information needed for the design of melon seed pyrolysis processes.

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.

Kinetics of thermal degradation of intumescent flame-retardant spirophosphates

The thermal degradation behaviour of various spirophosphates synthesized using SDP (phenol), SDOC (o-cresol), SDMC (m-cresol), SDPC (p-cresol), SDDMP (2,4-dimethylphenol) and SDTMP (2,4,6-trimethylphenol) with 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro-[5,5]-undecane-3,9-dioxide (SDCDP) are investigated using thermogravimetric analyzer. The spirophosphates show multistage degradations in the temperature range 180–550°C. The second stage of degradation is more prominent and the substituent effect is clearly reflected at this stage of degradation. The compound SDP showed superior performance since it has the greatest char yield value (44%) and LOI value (27%). The model free kinetic methods of Flynn-Wall-Ozawa and Vyazovkin methods are used to calculate the apparent energy of activation for the thermal degradation (Ea-D) of these spirophosphates. The material SDTMP showed the highest Ea-D values.

THERMAL BEHAVIOUR KINETIC MODELING OF CAPSICUM ANNUUM WASTE BIOMASS USING AN ISO-CONVERSION METHOD

In the present study, the pyrolysis behaviour of Capsicum Annuum stem Waste (CAW) was studied applying thermogravimetric analysis to evaluate the intrinsic kinetic parameters to develop a pyrolysis reactor for utilizing CAW. The thermal decomposition of CAW was achieved between 373 – 1173 K under inert conditions at different heating rates of 10, 20, and 30 K min-1. Model-free kinetic methods like Kissinger-Akahira-Sunose (KAS), Ozawa Flynn Wall (OFW) and Coats Redfern methods were applied to work out the kinetic parameters. To identify the utility of CAW and its biochar, physio-chemical characteristics such as proximate and ultimate analysis, scanning electron microscopy, and Fourier Transform Infrared analysis are reported.

Pyrolysis behaviors, kinetics and gaseous product evolutions of two typical biomass wastes

Rice husk (RH) and poplar bark (PB) as the staple biomass wastes represent herbaceous and woody plants, respectively. Thermo-chemical conversion of these wastes is a practical approach for value-added reclamation of bioenergy in large-quantity and pyrolysis plays core role in this process. In this work, RH and PB were subjected to comprehensive investigations on pyrolysis behavior, kinetics and gaseous product evolution in a thermogravimetry-Fourier transform infrared spectroscopy at different heating rates. The results demonstrated that both RH and PB underwent three consecutive pyrolysis stages, the TG/DTG curves shifted to higher temperature and the peak temperature intervals also enhanced as heating rate increased. It was observed CO2 was the most dominated species among oxygenated products, followed by CO bond containing species, while CH4 and arenes were abundant in hydrocarbon gases. In comparison, pyrolysis of RH could generate larger amounts of oxygenated products, and more hydrocarbons like CH4, arenes, and C2+ aliphatics were observed in the pyrolytic products of PB. Model-free kinetic methods showed that the average Ea were 209.1 kJ/mol and 203.9 kJ/mol for RH and PB, respectively. Criado model-fitting method indicated that pyrolysis of RH and PB both obeyed F1 reaction mechanism first and turned into one-dimensional diffusion and reaction mechanism, respectively at higher conversion of 0.25−0.60.

Aromatic dialdehyde-based bisbenzoxazines: The influence of relative position of oxazine rings

Polybenzoxazines are known to have superior thermal stability. Especially, the use of aromatic aldehydes instead of formaldehyde for the synthesis of benzoxazines monomers could improve this stability. However, the increase in aromatic content of the monomer can prevent the processability. The objective of this article is to understand the relationships between the conformation of an aromatic dialdehyde and its thermal properties. Two benzoxazine monomers were synthesized, based on salicylaldehyde, furfurylamine and respectively terephthalaldehyde (TPA, para configuration) and isophthalaldehyde (IPA, meta). Structural characterizations showed differences in intramolecular interactions between the two isomers. The melting transition of “meta” isomer was 50 °C lower than for “para” monomer, whereas polymerization temperatures and enthalpies were nearly the same. Volatile compounds released during the polymerization were the same in both cases, as investigated by mass spectrometry (Py-GC/MS). Curing kinetics using model-free kinetic methods revealed that the E-dependency follows the same trend for both monomers. Finally, thermal degradation monitored by thermogravimetric analysis under inert atmosphere was similar, with high degradation temperatures and high char yields (64%).

Evaluation of the Validity of Model-Fitting and Model-Free Methods for Kinetic Analysis of Nonisothermal Pyrolysis of Siberian Fir Bark

The kinetic parameters of the pyrolysis of Siberian fir bark were estimated by thermogravimetric analysis. The thermochemical conversion of the bark biomass was performed at heating rates of 5, 10, and 20 deg/min in an inert (argon) medium. The results of thermogravimetric and differential thermogravimetric analyses were studied by model-fitting (Arrhenius and Coats–Redfern) and model-free (Friedman and Ozawa–Flynn–Wall) kinetic methods. The most reliable values of the activation energy were obtained by the model-free Ozawa–Flynn–Wall and Friedman methods (159 and 156 kJ/mol, respectively). It was shown that using these kinetic models enables one to determine more accurate temperature ranges of decomposition of biomass components under pyrolysis conditions.

Kinetic study and pyrolysis: GC/MS products analysis of Spirulina platensis cultivated under a different growing medium

Microalgae have a great potential to produce biofuels, but the cost is still too high mainly due to the biomass production. Mixotrophic cultivation has been pointed as microalgae cultivation mode for biomass/bioenergy production with lower cost. The proposals of this work were to cultivate S. platensis in autotrophic and mixotrophic medium using molasses as source of organic carbon and investigate the thermal behavior of obtained biomass by means of thermogravimetric analysis and pyrolysis (Py-GC/MS). The kinetics models proposed by Flynn and Wall and model-free kinetic were used to determine the activation energy. These data are important to projection of design, operation and modeling of thermochemical conversion system for microalgae. The use of molasses as supplement in culture medium for the growth of S. platensis was a good way to increase the biomass productivity and decrease the protein content. The Flynn–Wall and model-free kinetic methods were adequate to calculate activation energy on the conversion range of 0.20 to 0.80. The activation energies were 168–229 kJ mol−1 (Flynn and Wall), 177–238 kJ mol−1 (model-free kinetic) for mixotrophic biomass and 174–220 kJ mol−1 (Flynn and Wall), 181–229 kJ mol−1 (model-free kinetic) for autotrophic biomass. The compositions of volatile compounds produced by S. platensis biomass pyrolysis were different due to cultivation method that influenced the composition of biomass. Hydrocarbons, oxygenated and nitrogenated compounds were produced with different quantities. The volatile compounds content of phenols, oxygenated and nitrogenated increased and non-aromatic and aromatic hydrocarbons content decreased for pyrolysis of mixotrophic biomass. However, the mixotrophic cultivation has a great influence on the microalgae biomass production and should be a factor considered in thermal degradation project for microalgae.

Analysis of the pyrolysis kinetics of wastewater-fed microalgal biomass by a parallel order-based reaction model

ABSTRACT Wastewater-fed microalgal biomass has attracted a considerable interest for biofuel production via pyrolysis in recent years. In this study, thermal degradation behavior and pyrolysis kinetic parameters have been investigated by non-isothermal thermogravimetric analysis. Analysis of the reactive phase showed two partially overlapping devolatilization stages, with degradation peaks at 540–570 K, accompanied by a shoulder at around 590–615 K, and 735–785 K, respectively. Model-free kinetic methods showed a large variation in the activation energy with the conversion degree, suggesting a multi-step reaction scheme. Consequently, a parallel order-based reaction model of three pseudo-components (proteins, carbohydrates and lipids) was applied, showing a good agreement with the experimental data. Based on this approach, the average activation energies were 143, 166 and 61 kJ·mol−1 for proteins, carbohydrates and lipids, respectively, while the average orders of reaction were 2.3, 1.6 and 0.6.