Mean Activation Energy Research Articles

Evaluation of thermal stability and kinetic of degradation for levodopa in non-isothermal conditions

In this paper, we present the results obtained during the investigation of thermal stability of antiparkinsonian drug Levodopa in oxidative atmosphere and under non-isothermal conditions. As investigational tools, thermoanalytical methods were used along with ATR-FTIR spectroscopy and later completed with kinetic study for the main degradative process that occurs in the 260–330 °C temperature range, at four heating rates. Four kinetic methods were used as follows: ASTM E698 which leads to an activation energy of 209.72 kJ mol−1, while isoconversional methods suggested the values 177.6 ± 13.1 kJ mol−1 (Friedman) and 188.8 ± 4.5 kJ mol−1 (Kissinger–Akahira–Sunose), with a clear indication of multistep degradation. The last method used was NPK, which revealed that the degradation occurs in three steps, with different physical and chemical contributions with mean activation energy equal to 191.3 ± 9.5 kJ mol−1.

Analysis of pyrolysis characteristics and kinetics of Euphausia superba shell waste using TG-FTIR and distributed activation energy model

Pyrolysis of Euphausia superba shell waste (ESW) was investigated by using a thermogravimetric analyzer coupled with a Fourier transform infrared spectrometer (TG-FTIR). The kinetic parameters of pyrolysis reactions were obtained via the distributed activation energy model (DAEM). Experimental results showed that the temperature at which the highest weight loss rate occurred increased from 280 to 315 °C as the heating rate increased from 5 to 30 °C min−1. Almost all the volatiles were evolved between 300 and 350 °C, while CH4 and aliphatic C–H were also produced at higher-temperature regions. A large amount of CO2 was generated above 650 °C by the decomposition of carbonates, and it can be further reduced to CO by ESW char. CO2 was the main non-condensable product, and ketones were the dominating condensable products. The activation energy of pyrolysis reactions increased from 79 to 392 kJ mol−1 for conversion rates 0.13 to 0.54. The linear relationship between the natural logarithm of the frequency factor and activation energy was also established. The activation energy approximately followed Gaussian distribution, and the mean activation energy was 162 kJ mol−1.

Simulation of Roasting Metallurgical Concentrates in Fluidized Bed Using CFD-DEM

In this study, we utilized multiphase computational fluid dynamics (CFD), and discrete element method (DEM). Effect of the kinetic parameters of the roasting process in a fluidized bed was investigated. Our results indicate that it is possible to numerically integrate the coupled CFD-DEM system without significantly increasing computational overhead. It is also clear, however, that reactor operating conditions, reaction kinetics, and multiphase flow dynamics have major impacts on the roasting products exiting the reactor. We find that, with the same pre-exponential factors and mean activation energies, inclusion of distributed activation energies in the kinetics can shift the predicted average value of the exit gas-solidphase and its statistical distribution, compared to single-valued activation-energy kinetics. These findings imply that accurate resolution of the reaction activation energy distributions will be important for optimizing roasting processes.

An innovative evaluation method for kinetic parameters in distributed activation energy model and its application in thermochemical process of solid fuels

The interaction among kinetic parameters in the distributed activation energy model was investigated. The surface and contour plots of prediction error were depicted to explain non-uniqueness of the kinetic parameters. The kinetic compensation effect between mean activation energy and pre-exponential factor was confirmed based on the isokinetic point. An innovative estimation method for kinetic parameters was proposed, which not only eliminated the non-uniqueness of kinetic parameters but also ensured that the model owns a robust predicting ability. The Maximum Likelihood Estimation was used to estimate the mean activation energy. A combination of Gauss-Hermite Quadrature numerical algorithm and pattern search method was applied to determine the pre-exponential factor and standard deviation. In addition, the developed method was successfully employed to estimate the pyrolysis kinetics of sewage sludge. The new method will promote the application of the distributed activation energy model in the thermochemical utilization of solid fuels.

Effect of Temperature on the Kinetics of the Activation of Treosulfan and Hydrolytic Decomposition of Its Active Epoxy Derivatives

Treosulfan (TREO) is a prodrug applied in the treatment of ovarian cancer and a myeloablative conditioning prior to stem cell transplantation. A sequential activation of TREO to intermediate monoepoxide (S,S-EBDM) and then to (2S,3S)-1,2:3,4-diepoxybutane (S,S-DEB) involves a nonenzymatic intramolecular nucleophilic substitution. The aim of this study is to determine the effect of temperature on the rate constants (k) for the activation of TREO and the hydrolysis of its epoxy derivatives in a phosphate buffer of pH 7.4 at an ionic strength of 0.16-0.17 M. Over the tested temperature range, the ln of k changed linearly with a reciprocal of absolute temperature. The mean activation energy (Ea) values for the TREO → S,S-EBDM and S,S-EBDM → S,S-DEB reactions were close to each other (122 and 118 kJ/mol, respectively). In opposition, the Ea for the hydrolysis of S,S-EBDM and S,S-DEB differed significantly (140 and 80 kJ/mol, respectively), which indicates that the structure of S,S-EBDM hampers a nucleophilic attack of water on the epoxide ring. The obtained results show that a temperature change by 1°C, from 36.5°C to 37.5°C, entails a 17% increase in the k of TREO decay, which might lead to an increased TREO clearance in vivo.

Bio-fuel oil characteristic from catalytic cracking of hydrogenated palm oil

Pyrolysis characteristic of hydrogenated palm oil (HPO) was analyzed using TG, TG-FTIR-MS and Py-GC-MS. Bio-fuel oil (BFO) was obtained using catalytic cracking method. The BFO was analyzed by FTIR, 1H NMR, 13C NMR, GC-MS and ESI FT-ICR MS to provide complementary and comprehensive adequate information. TG-DTG results showed that the HPO pyrolysis was different with other plant oil. It was clear that HPO pyrolysis was mainly in temperature range of 350 °C–500 °C. The mean activation energy of HPO pyrolysis calculated from KAS and FWO models was 161.10 kJ/mol and 164.28 kJ/mol, respectively. According to TG-FTIR-MS results, little amount of gas components was detected. Py-GC-MS result found heavy compounds, which carbon number exceeds 18. FTIR, 1H NMR, 13C NMR and GC-MS results found the BFO mainly contained long-chain alkane and alkene. According to ESI FT-ICR MS, the oxygen containing compounds in BFO were from O2O6 classes, with the O2 being the major class. The RSFTIR was first used to analyze biomass pyrolysis. The results found that in the decarboxylation process, the carbon chain also was cracked to form short carbon chain carboxyl firstly. According to above experiments results, we can confirm HPO pyrolysis path was different with palm oil. The key conclusion was that HPO maybe was a good bio-resource to obtain BFO, and it was mainly contained diesel-like components. Compared to palm oil pyrolysis products, HPO pyrolysis products were mainly contained long-chain alkane and alkene. The recommended pyrolysis path was also proposed.

Kinetic Parameters for the Thermal Decomposition of Forest Waste Using Distributed Activation Energy Model (DAEM)

Abstract The purview of paper pivoted around the pyrolysis decomposition of forest waste (pine needle litter) by thermogravimetric analysis (TGA). Experiments were carried out in the presence of Nitrogen atmosphere. The experimental data was compared with those obtained by numerical solution of distributed activation energy model (DAEM). Asymptotic expansion is adopted to evaluate the pre-exponential factor, mean activation energy and variance. The correction factor Bi has been invoked to describe accurately the differential thermogravitmeric curves of thermal decomposition of pine needles.

Kinetics of magnetite oxidation under non-isothermal conditions

Oxidation of magnetite concentrates, which occurs during the pellet induration process, must be deeply understood to enable the appropriate design of induration machines. In the present paper, the kinetics of the magnetite oxidation reaction was studied. Primary samples were obtained from the Gol-e-Gohar iron ore deposit. Magnetic separation and flotation decreased the sulfur content in the samples to be approximately 0.1wt%. Thermogravimetric analysis was used to measure mass changes during the oxidation of magnetite and, consequently, the conversion values. The aim of this study was to use isoconversional methods to calculate the kinetic parameters. The Coats–Redfern method was also used to obtain the activation energy. Thermogravimetric analyses were run at three different heating rates. The Coats–Redfern results were too ambiguous for a meaningful interpretation. In the case of the isoconversional method, however, the mean activation energy and pre-exponential factor of the oxidation reaction were obtained as 67.55 kJ and 15.32 × 108 min−1, respectively. Such a large activation energy implies that temperature strongly affects the reaction rate. The oxidation reaction exhibits a true multi-step nature that is predominantly controlled by chemical reaction and diffusion mechanisms.

Kinetic study on the pyrolysis and gasification of plastic waste

With the large volume of consumer plastic waste generated worldwide, one common problem in the Philippines involves the disposal and treatment of solid wastes. Current processes in the disposal of post- consumer plastic wastes such as incineration or landfill are not fully acceptable based on international standards. As such, there is an urgent need for a practical, safe and efficient disposal method which can also convert waste into useful energy. Pyrolysis and gasification are very well-known thermal degradation processes that convert carbonaceous materials into useful gaseous products that still contain significant amount of energy. The parameters obtained from the kinetic study of these processes are very essential in the design of useful conversion technologies such as reactors and gasifiers. In this study, the pyrolysis and gasification of plastic waste samples were investigated in a thermogravimetric analyser (TGA).The kinetic parameters for the pyrolysis of the samples were obtained at heating rates ranging from 10 - 30 K/min. The mean activation energies for the pyrolysis reaction were found to be 124.1 kJ/mol and 107.3 kJ/mol, for samples X and Y. In terms of the temperature at which maximum degradation occurs, the differential thermogravimetric (DTG) curve of the plastic waste sample resembles that of a ternary mixture containing polypropylene (PP), polyethylene (PE) and polyethylene terephthalate (PET). For the gasification of the plastic waste samples with CO2, a temperature higher than 600 °C is required to attain significant conversion. The activation energies for the gasification of the waste plastic samples were found to be 144.7 and 147.8 kJ/mol for samples X and Y.

Thermal decomposition kinetics of sugarcane mills wastes

The aim of this work was to evaluate the kinetic parameters regarding the first thermal decomposition mass loss step of organic matter present in samples of bagasse, filter cake, and vinasse provided by two sugarcane mills by TG in pyrolysis and combustion conditions. LL-INT Wanjun–Donghua procedure modified by Capela–Ribeiro was employed to estimate activation energy in function of the extent of conversion. The chemical composition of samples was determined by ultimate analysis, FTIR spectroscopy, X-ray diffractometry, and atomic absorption spectrophotometry among other analytical techniques. Results indicated that despite similar organic composition, the energetic potential of filter cake and vinasse was lower than that of bagasse due to their increased inorganic content. Filter cake presented high amounts of Ca, Cu, Fe, Mn, P, and Zn. Vinasse showed greater concentrations of Na and K and higher amounts of other metals such as Ca, Mg, Mn and Zn than bagasse and filter cake samples. Filter cake and vinasse samples had significant concentrations of heavy metals like Cr and Pb. However, considerable differences were observed when the chemical composition of samples from a same type of waste was compared. Different kinetic mechanisms of reaction were observed for a same kind of waste which resulted in variation of mean activation energy values. Regarding this parameter, samples that were subjected to nucleation presented lower values than the ones that showed geometrical contraction. The order-based models were responsible for the elevation of activation energy. Despite these facts, the kinetic compensation effect was observed for all samples in both pyrolysis and combustion atmospheres.

The study of RDX impurity and wax effects on the thermal decomposition kinetics of HMX explosive using DSC/TG and accelerated aging methods

The thermal decomposition kinetic behavior of three HMX explosive samples containing 5.0 mass% (A-HMX) and 0.5 mass% RDX impurity (B-HMX) and HMX desensitized with 5.0 mass% paraffin wax (W-HMX) was studied by non-isothermal differential scanning calorimetric and thermogravimetric techniques at different temperature scan rates and by isothermal accelerated aging method. Using KAS isoconversional method, the mean activation energies of 229.36, 221.05, and 267.37 kJ mol−1 were obtained for B-HMX, A-HMX, and W-HMX, respectively, showing the higher thermal stability of pure and desensitized HMX. Moreover, the reaction mechanism was found in Avrami–Erofeev A2 model for all samples. In this study, by using the calculated kinetics triplets, the chemical lifetime of explosives were predicted based on 5.0 mass% mass loss and were compared with isothermal accelerated aging results, under two constant temperatures. The experimental results in the higher temperatures demonstrated relatively better consistency with predicted values.

Static Recrystallization Kinetics and Crystallographic Texture of Nb-Stabilized Ferritic Stainless Steel Based on Orientation Imaging Microscopy

In the present study, Nb-stabilized ferritic stainless steel was prepared with annealing (430-A) and without annealing (430-NA) annealing, and the microstructure of the resulting samples was examined. The steel was then subjected to cold rolling and isothermal annealing in order to analyze its recrystallization kinetics and texture evolution. Microstructural characterization was performed by scanning and transmission electron microscopies. Recrystallization kinetics were evaluated by measuring the microhardness of the samples, and analyzing their kernel average misorientation and grain orientation spread via electron backscatter diffraction. The Avrami exponent data revealed that one-dimensional grain growth occurred owing to the migration of high-angle grain boundaries. The mean activation energies for recrystallization for 430-NA and 430-A was found to be 365 and 419 kJ mol−1, respectively. The recrystallization texture was influenced by oriented nucleation and selected growth mechanisms, as well as by the Nb carbonitride distribution and grain boundary energy. The recrystallized and growing grains with the {554}〈225〉 orientation showed a dimensional advantage over the other recrystallized components. The coincident site lattice boundaries were attributed to the progression of recrystallization since the CSL numeric fraction increased as the temperature increased. The {554}〈225〉 component was associated with the ∑19a boundary, which exerted a significant control on the selective growth during the recrystallization.

Elucidation of the Influence of Coal Properties on Coal-Char Reactivity: A Look at Southern Hemisphere Coals

Pyrolysis is the first step in most coal conversion processes such as combustion, gasification and liquefaction. Coal char combustion is influenced by a wide variety of parameters (burnout time, heat release, mineral matter content etc.) which are factored into the reactivity of the char. On heat treatment, the coal particles undergo thermochemical decomposition with liberation of tars and volatiles and the formation of a resultant char. The reactivity of the char is dependent on both the physical and chemical changes that accompanying heat treatment of the coal particles. The char reactivity exhibited the same trend of decrease with increasing pyrolysis temperature for the four temperature program used in this evaluation. The derived aromaticity, total reflectance, surface area and porosity were found to increase with increasing pyrolysis temperature. The activation energy of the various chars were also determined with an mean activation energy of 184 for lignite, 154 for sub-bituminous, 94 for low volatile bituminous, 146 for high volatile bituminous, 113 for semi-anthracite and 152 KJ/mol for the anthracite coal respectively.

Anticipating hyperthermic efficiency of magnetic colloids using a semi-empirical model: a tool to help medical decisions.

Magnetic hyperthermia, a modality that uses radio frequency heating assisted with single-domain magnetic nanoparticles, is becoming established as a powerful oncological therapy. Much improvement in nanomaterials development, to enhance their heating efficiency by tuning the magnetic colloidal properties, has been achieved. However, methodological standardization to accurately and univocally determine the colloidal properties required to numerically reproduce a specific heating efficiency using analytical expressions still holds. Thus, anticipating the hyperthermic performances of magnetic colloids entails high complexity due to polydispersity, aggregation and dipolar interactions always present in real materials to a greater or lesser degree. Here, by numerically simulating the experimental results and using real biomedical aqueous colloids, we analyse and compare several approaches to reproduce experimental specific absorption rate values. Then, we show that the relaxation time, determined using a representative mean activation energy consistently derived from four independent experiments accurately reproduces experimental heating efficiencies. Moreover, the so-derived relaxation time can be used to extrapolate the heating performance of the magnetic nanoparticles to the other field conditions within the framework of the linear response theory. We thus present a practical tool that may truly aid the design of medical decisions.

Thermal decomposition and kinetics of plastic bonded explosives based on mixture of HMX and TATB with polymer matrices

Abstract This work describes thermal decomposition behaviour of plastic bonded explosives (PBXs) based on mixture of l,3,5,7-tetranitro- 1,3,5,7-tetrazocane (HMX) and 2,4,6- triamino-1,3,5-trinitrobenzene (TATB) with Viton A as polymer binder. Thermal decomposition of PBXs was undertaken by applying simultaneous thermal analysis (STA) and differential scanning calorimetry (DSC) to investigate influence of the HMX amount on thermal behavior and its kinetics. Thermogravimetric analysis (TGA) indicated that the thermal decomposition of PBXs based on mixture of HMX and TATB was occurred in a three-steps. The first step was mainly due to decomposition of HMX. The second step was ascribed due to decomposition of TATB, while the third step was occurred due to decomposition of the polymer matrices. The thermal decomposition % was increased with increasing HMX amount. The kinetics related to thermal decomposition were investigated under non-isothermal for a single heating rate measurement. The variation in the activation energy of PBXs based on mixture of HMX and TATB was observed with varying the HMX amount. The kinetics from the results of TGA data at various heating rates under non-isothermal conditions were also calculated by Flynn–Wall–Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. The activation energies calculated by employing FWO method were very close to those obtained by KAS method. The mean activation energy calculated by FWO and KAS methods was also a good agreement with the activation energy obtained from single heating rate measurement in the first step decomposition.

Pyrolysis and kinetic behavior of banana stem using thermogravimetric analysis

ABSTRACTPyrolysis and kinetic behavior of banana stem (BS) were investigated using thermogravimetric analysis (TGA). The behavior of mass loss demonstrated that pyrolysis process of BS appeared in three stages with a conversion range of 0–0.20, 0.20–0.90, and 0.90–1, respectively. The reaction mechanism of BS pyrolysis followed the 3D diffusion model, with an apparent activation energy range of 130.63–192.10 kJ/mol and a pre-exponential factor range of 2.42×107–4.10 × 1010 s–1. Stages 1, 2, and 3 were mainly attributed to pyrolysis of hemicellulose, cellulose, and lignin with mean activation energies of 139.09, 155.41, and 188.71 kJ/mol, respectively. The experimental data obeyed the iso-conversional model well with correlation coefficients (R2) over than 0.9928.

Kinetics Modeling of Low-Rank Coal Pyrolysis Based on a Three-Gaussian Distributed Activation Energy Model (DAEM) Reaction Model

A three-Gaussian distributed activation energy model (DAEM) reaction model (3-DAEM) was successfully applied for the kinetics study on the thermal pyrolysis of four types of low-rank coals, based on their nonisothermal thermogravimetric data. It is found that 3-DAEM was feasible for the analysis of coal pyrolysis process, which can be divided into three stages, using the second derivative method for thermogravimetry (TG) curves and the Peakfit software for differential thermogravimetry (DTG) curves. Calculated kinetic parameters, including three mean activation energies (E0), three standard deviations (σE), and two weights (w), were used to predict the pyrolysis process, and the results agreed well with the experimental data. Furthermore, the kinetics parameters were found to have a strong relationship with the DTG curve shape and especially with the coal property. These results indicated that 3-DAEM provided a good way to process thermogravimetric analysis (TGA) data and understand the pyrolysis mechanis...

Synergistic effect on thermal behavior and char morphology analysis during co-pyrolysis of paulownia wood blended with different plastics waste

Thermal behavior of Paulownia wood (PAW), model plastics (polypropylene, polyvinyl chloride and polyethylene terephthalate, abbreviated as PP, PVC and PET) and their mixtures during pyrolysis process were studied through thermogravimetric analyzer. Scanning electron microscopy technology (SEM) and fractal theory were applied to evaluate the surface morphology of pyrolysis chars. This study found that PP showed synergistic effect on PAW pyrolysis with more volatiles release than predicated value, and the maximum volatiles yield exhibited with 25% PAW blending ratio. However, higher char yields were observed compared with the predicted values during co-pyrolysis process of PAW blends with PVC or PET, and the maximum char yields were obtained under the PAW blending ratio of 75% and 25% respectively. An evident decline in mean activation energy was found during co-pyrolysis of the PAW blending with plastics. The minimum values of mean activation energy for the PAW/PP, PAW/PVC and PAW/PET were gained when the PAW blending ratio were 75%, 50% and 75% respectively. Quantitative information about surface topography of pyrolysis chars were obtained by fractal analysis of the SEM microphotograph. The fractal dimension of residual chars from PAW/PP blends increased from 1.75 to 1.84 as increasing the ratio of PP from 25% to 75%, indicating that PP addition promoted the nonuniformity of the co-pyrolysis chars. The surface morphology of residual chars from PAW/PET and PAW/PVC blends showed a contrary tendency, and the minimum values of fractal dimension were respectively 1.62 and 1.61 under 25% PAW blending ratio.

Thermoanalytical measurements conducted on repaglinide to estimate the kinetic triplet followed by compatibility studies between the antidiabetic agent and various excipients

Repaglinide is an antidiabetic agent that is used in the treatment of the type II diabetes mellitus. In this study, we aimed to determine the thermal behavior of this pharmaceutical agent, as well as the kinetic parameters that characterize the main degradation process of repaglinide. We also targeted a study in which the compatibility of repaglinide with various excipients was evaluated by thermoanalytical and spectrometric techniques. In order to determine the kinetic triplet of the degradation process, the repaglinide was submitted to a controlled degradation process under a temperature program from 40 to 500 °C in air flow of 100 mL min−1 and according to ICTAC 2000 Protocol, samples were heated at five different heating rates: β = 5, 7, 10, 12 and 15 °C min−1, respectively. All data were computed by four isoconversional kinetic methods: FR, FWO, KAS and modified NPK. The compatibility studies implied preparing the binary mixtures of repaglinide and different excipients using a mass ratio of 1:1. For the thermoanalytical evaluation samples of the mixture were analyzed following a temperature program from 40 to 500 °C in air flow of 100 mL min−1 with a heating rate of 10 °C min−1. The spectrometric analysis was performed using the same type of mixtures. The studies show a good compatibility between repaglinide and the five excipients used and also well correlated values of the mean activation energy obtained by FWO, KAS and modified NPK methods.

Atomic-scale investigation of triple junction role on defects binding energetics and structural stability in α-Fe

Nanocrystalline (NC) metals (mean grain sizes d ≤ 100 nm) have enhanced mechanical strength as compared to coarse-grained metals (d ≥ 1 μm), and thus, are a promising alternative as structural materials for future high energy nuclear reactors. However, during extreme conditions, the NC microstructure has been found to be thermodynamically unstable, thereby limiting its applicability. Further, for materials with average grain size <10 nm, the triple junctions (TJs) have been observed to have a significant contribution on the mechanical behavior and microstructural stability. Moreover, at the atomic-scale, the region surrounding the TJ demonstrates unique physical properties, such as rapid diffusion, non-equilibrium segregation and increased dislocation activity. Therefore, in this work, we systematically assess the role of TJs on the structural stability and the solute binding behavior in α-Fe. Using atomistic simulations, we show that the TJ resolved line tension is strongly correlated (inversely) with the mean activation energy for self-diffusion along the TJ, i.e., the thermodynamically unstable TJs demonstrated a lower activation energy barrier for self-diffusion along TJs with higher line tension. Next, we demonstrated that the strain energy evolution around the TJ can provide insights into the distinct binding behavior of point defects and solute atoms. In other words, the examination of solute binding behavior revealed a localized region of stable sites around the TJs which aids in accommodation of high solute concentration at high temperatures. In summary, our findings quantify the distinct role of TJs on the defect (vacancy, self-interstitial and solute atom) binding and migration behavior and these findings are necessary for designing future structural materials for extreme environments, including those needed in aerospace, naval, civilian and energy sector infrastructures.