Distribution Of Activation Energies Research Articles

Magnetic interactions in Co2+ doped ZnO synthesised by co-precipitation method: Efficient effect of hydrogenation on the long-range ferromagnetic order

Abstract Zinc oxide doped with different concentrations of Co2+ ions (ZnO:Co) nano-powders were synthesised by co-precipitation method using complexes zinc acetate dihydrate and cobalt acetylacetonate. The mass ratios of Co/Cd in the investigated samples were 0.5% 1%, 2%, and 3%. The X-ray diffraction (XRD) study confirmed the formation of single-phase crystalline hexagonal Wurtzite structure, thus, Co ions were successfully doped into ZnO lattice forming substitutional solid solutions. The purpose of the present study is to synthesise and investigate the possible creation of room-temperature ferromagnetic (RT-FM) properties in host ZnO for DMS applications. The magnetic analysis has showed that the magnetic behavior of the as prepared ZnO:Co samples is dominated by a paramagnetic component over ferromagnetic component, which is an indicative of dominant uncoupled Co spins. However, the same samples exhibited pronounce room temperature ferromagnetic behavior (RTFM) when they were hydrogenated, which was attributed to the role of oxygen vacancies (VO) in accordance with the Bound Magnetic Polaron Model (BMP). Furthermore, the analysis of the magnetization reversal via fluctuation fields for the hydrogenated samples shows that the distribution of activation energies arises from both, the dispersion of anisotropy fields and the sizes distribution of FM ordered regions. Due to the dispersion of anisotropy fields, the mediated exchange coupling through vacancies at low ions concentrations provide stronger RTFM behavior than the highly concentrated ones. Accordingly, it believed that increasing the ions concentrations to enhance the direct ions coupling may destabilize the polarons structure and then weaken the irreversible magnetic behavior.

Thermogravimetric characteristics and kinetics of sawdust pyrolysis catalyzed by potassium salt during the process of hydrogen preparation

Pyrolysis experiments of sawdust with KOH and K2CO3 catalysts were carried out under different heating rate in nitrogen atmosphere using thermogravimetric analyzer. The distributed activation energy model (DAEM) was used to analyze pyrolysis kinetics of sawdust. The results showed that both KOH and K2CO3 had strong catalytic effect on sawdust pyrolysis, which reduced the pyrolysis temperature of sawdust and increased the yield of char. There was only one main peak in DTG curve, which means that the pyrolysis behavior of cellulose and hemicellulose in sawdust was greatly changed. The catalytic performance of KOH was found to be more excellent in sawdust pyrolysis. Also KOH could catalyze the pyrolysis of sawdust at low temperature. The kinetic analysis results showed that the two kinds of catalysts could reduce the activation energy of sawdust pyrolysis and maintain a similar catalytic trend, but KOH had a more stable catalytic performance.

Catalytic performance of potassium in lignocellulosic biomass pyrolysis based on an optimized three-parallel distributed activation energy model

The pyrolysis kinetics of extractive tobacco stem and pretreated samples with different KCl impregnation ratios were investigated by the thermogravimetric experiment and an optimized three-parallel distributed activation energy model (DAEM). The significant fitting deviation for the cellulose pyrolysis and the unrealistic partial fitting curve for the hemicellulose pyrolysis were mitigated during the optimization process by applying the Avrami-Erofeev-DAEM and reducing the latent interferences. The optimized parameters with good fitting qualities (about 2%) were obtained. Furthermore, based on the experimental results (changes in reaction intensity and temperature), model calculations (differences in reaction order, activation energy, volatiles fraction, etc.), and the maximum residual error analysis (with a high catalytic reaction rate) regarding different KCl-to-biomass ratios, it was found that KCl kinetically promoted the hemicellulose pyrolysis, which can be utilized as the theoretical support for the industrial application.

Gasification mechanism and kinetics analysis of coke using distributed activation energy model (DAEM)

This work studied the gasification reaction of four different metallurgical cokes (Coke-A, Coke-B, Coke-C, Coke-D) with CO2 by the thermogravimetric analysis. The physical, chemical and structure features were also analyzed systematically. It is found that with increasing the heating rate, the conversion curves move to high temperature for all these four cokes, and the maximum gasification rate also increases. Meanwhile, at the same heating rate, the gasification reactivity of these four cokes is ordered as: Coke-D > Coke-C > Coke-B > Coke-A. According to the component and structural analysis, the gasification reactivity was mainly due to the microcrystalline structure of the carbon in the coke, and the gasification reactivity of coke increases when the content of amorphous carbon increases. Comparing with the single-step global model, the distributed activation energy model (DAEM) is more accurate to characterize the gasification kinetics for the studied cokes, and the activation energies are in the range of 159.8–254.1 kJ/mol.

Thermal behavior and kinetics of pyrolysis of areca nut husk

ABSTRACTPyrolysis of agricultural crop residues is making rapid strides in the overall lignocellulosic biomass utilization for the recovery of energy. In the present work, physicochemical properties of areca nut husk such as proximate and ultimate analysis, lignocellulosic composition, and thermal analysis have been carried out. Pyrolysis of areca nut husk was studied using thermogravimetric analysis to determine the kinetic parameters at five different heating rates, viz. 2, 5, 10, 15, 20°C/min. The major mass loss (44.4 wt%) of AH was found to be in the temperature range of 220–370ºC. The kinetic parameters pertaining to pyrolysis of areca nut husk were calculated using distributed activation energy model (DAEM) and model-free isoconversional Flynn-Wall-Ozawa (FWO) method. Miura and Maki integral method was employed to estimate f(E) and k0(E) in this study. The peak of f(E) curve for the areca nut husk was obtained at 240 kJ/mol and the frequency factor (k0) increased from an order of 1013–1022 min−1, while the activation energy ranged from 87.5 to 514.08 kJ/mol. The variation in activation energy values with progressing conversion indicates the existence of a complex multi-step mechanism that occurs during the thermal decomposition of AH. The average activation energy obtained by FWO method was 230.707 kJ/mol (with a range of 62.35–591.972 kJ/mol) which is close to 240 kJ/mol obtained via DAEM method from f(E) curve and hence the results can be said to be reliable and predictive.

Experiment and expectation: Co-combustion behavior of anthracite and biomass char

The combustion behavior of anthracite, biomass (Ficus virens) char and their blends were investigated by thermogravimetry analysis (TGA). The combustion process mainly focused on the volatile combustion and char combustion. The addition of char reduced the initial temperature and final temperature of fuels. The interactions firstly inhibited and then facilitated. When the blending ratio was 70AN30FV, the antagonism was the minimum, and synergism was the strongest at 830 K for the random ratio. The kinetic models of Coats-Redfern (CR), Doyle equation (Doyle), Friedman (FR), Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and distributed activation energy model (DAEM) were used to calculate the kinetic parameters. The average values of activation energy for CR and Doyle were close and that of KAS, FWO and DAEM were near. Based on these six models, the corresponding expectation equations of activation energy and pre-exponential factor were proposed and the best predicted results was CR model for 60AN40FV.

Reduction Kinetics of YBaCo4O7+δ Oxygen Carrier for Chemical Looping Air Separation

The kinetics of YBaCo4O7+δ and Y0.5Dy0.5BaCo4O7+δ oxygen carriers is determined using the experimental data obtained by fixed-bed apparatus. The results show that rate of oxygen release increases with the increase of reaction temperature. The mechanism function of reduction reaction is not affected Dy substituting. The Avrami-Eroféev mechanism function describes solid phase change of oxygen desorption adequately. The results show that the distributed activation energy of reduction process obtained by A model is about 29.72 kJ/mol and 23.30 kJ/mol for YBaCo4O7+δ and Y0.5Dy0.5BaCo4O7+δ oxygen carrier, respectively. The pre-exponential factor obtained is about 29.727 mol/(L·min) and 12.826 mol/(L·min) for YBaCo4O7+δ and Y0.5Dy0.5BaCo4O7+δ oxygen carrier, respectively.

An experimental investigation and kinetic‐modeling study of the phase transformation behavior of glycine in various carboxylic acids

AbstractIn this study, the phase transformation behavior from β‐glycine (Gly) to α‐Gly was examined in the presence of three different carboxylic acid additives (acetic, tartaric, and citric acid) at three different concentrations. Initially, the structure, morphology, shape parameters, surface functional groups, and elemental properties of the crystals prepared from the additive‐containing and nonadditive media were investigated. The characterization results showed that when compared with the pure medium, both the duration of the phase transformation and physicochemical properties of the α‐Gly crystals were altered in the presence of the three carboxylic acid additives studied. Subsequently, the experimental data obtained from the thermogravimetric analysis of the α‐Gly samples obtained from the additive containing and nonadditive media were modeled using a simplified DAEM kinetic model. On the basis of the data obtained from the distributed activation energy model, the average activation energy for the Gly crystals obtained from the pure medium was calculated to be 90.8 kJ/mol. The value for the crystals obtained from the acetic acid–containing medium was 104.0 higher than that found for the crystals from the pure medium and other two other additives studied. Besides kinetic analysis, thermogravimetric analysis/Fourier‐transform infrared spectroscopy and elemental analysis confirmed that the carboxylic acid was adsorbed on the crystal's surface. The amount of acetic, tartaric, and citric acid adsorbed was 2.97, 2.38, and 1.72 mg/g, respectively.

Specific kinetic triplet estimation of Tahe heavy oil oxidation reaction based on non-isothermal kinetic results

Although the oxidation mechanisms and kinetics characteristics of heavy oils have been involved in enormous studies, little attention is paid to the specific kinetics triplet and activation energy distribution in detailed temperature ranges. In this study, the non-isothermal oxidation kinetics characteristics of the Tahe heavy oil, including kinetics triplet, activation energy distribution (E-α curve) and thermodynamic parameters under specific temperature subzones, were investigated by thermo-analysis techniques and Popescu method. And it indicated that six sequential temperature subzones were identified with different mechanism function, G(α), and rate constant, k(T). Besides, it can be seen from the E-α curve that the first obvious increasing peak was attributed to the negative temperature gradient region (NTGR) and the second mild peak corresponded to the initiation stage of the combustion process, between which positive temperature coefficient and negative temperature coefficient zones were located at the valley. Additionally the calculated thermodynamic parameters (△S*, △H*, △G*) indicated that the non-isothermal oxidation process for Tahe heavy oil is the non-spontaneous reaction and needs heat to occur under atmospheric pressure.

Lacustrine Type I kerogen characterization at different thermal maturity levels: Application to the Late Cretaceous Yacoraite Formation in the Salta Basin – Argentina

A maturation series from the Late Cretaceous to Danian Yacoraite Formation in the Salta Basin (Argentina) was selected to investigate the evolution of organic matter properties from source rock samples mainly containing lacustrine Type I kerogen. Organic petrography determined the thermal maturity and the spatial distribution of organic matter particles. Rock-Eval analyses and kerogen isolation procedures were then applied to assess the hydrocarbon generation potential of the investigated intervals. Biomarker ratios as well as the molecular composition of organic compounds present in four immature to early-mature rock samples and their corresponding aliphatic and aromatic fractions were investigated to complete the lacustrine organic matter characterization. Based on petrographic results, immature to early-mature Yacoraite samples have a large content of yellow-brownish liptinites (alginites) whereas mature samples are characterized by abundant solid bitumen. Three kerogen samples from the Yacoraite Formation at different thermal maturity levels were also selected for analysis of bulk-kinetic parameters (e.g. activation energy distribution, frequency factor) using programmed open-system pyrolysis. In this way, bulk-kinetic parameters were calculated as a function of the thermal maturity for these three lacustrine kerogen samples. Bulk-kinetic results show both an increasing activation energy and loss of petroleum generation potential as thermal degradation proceeds. The investigated Yacoraite kerogen samples show single activation energy distributions which are typical for a Type I kerogen of lacustrine origin. Finally, it was demonstrated that the organic matter (OM) characteristics from the Yacoraite Formation (Argentina) could be compared to the typical Type I kerogen from the Green River Formation (USA), showing similar OM characteristics, petroleum potential and activation energy distributions. The novelty of the geological and geochemical information brought in this article about Yacaroite system in Argentina provides premises for further investigation.

Sodium humate as an effective inhibitor of low-temperature coal oxidation

In order to identify an accessible substance that efficiently prevents low temperature oxidation of coal which can lead to coal spontaneous combustion, this work investigated the use of sodium humate (SH) as a possible inhibitor of coal oxidation. Three coal samples (CJS, BZ and PING) were treated with sodium humate, oxidation of the coal during room temperature to 600 °C showed that the addition of sodium humate increases the initial exothermal temperatures (about 5–10 °C) and lower heat released (1692–2858 J/g) significantly. A distributed activation energy analysis showed that the presence of SH increased the activation energy barrier throughout the entire oxidation process, and the maximal incrasement enhanced by 29 kJ/mol. Combining these results with in situ FTIR analyses of functional groups on coal samples with and without SH, a mechanism for coal oxidation in the presence of SH is proposed. In this model, the addition of SH to the coal promotes the formation of hydrogen bonds and stabilizes ether groups, thus slowing the oxidation process. The results of this work suggest that SH is an effective inhibitor of coal oxidation.

Exploring the universality of the alternating conductivity of disordered materials using the Gaussian distribution of activation energies

This paper presents a new approach for the analysis of AC conductivity, = + , in disordered solids which brings together the quasi-universal frequency-dependent conductivity and the idea of a Gaussian distributions of probable activation energy barriers for hopping carriers. An explicit expression for AC conductivity was obtained using a complex dielectric response function and a continuous time random walk treatment applied to a lattice obeying the Kubo’s fluctuation-dissipation theorem. This expression provides an insight into the universality of the form and (k is the dielectric constant), as well into the effect of the Gaussian disorder on exponent s. We discuss the similarities and differences with the Random Free Energy Barrier model equivalent to the long-used box model, and it brings support to an extending expression proposed by J C Dyre and one of the authors. The applicability of the model to experimental observations on poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] reveals the dielectric constant, mean energy and variance of the Gaussian distribution for hopping carriers in this disordered conjugated polymer.

TGA/MS/FT-IR study for kinetic evaluation and evolved gas analysis of a biomass/PVC co-pyrolysis process

This study aims to investigate the thermal behaviours of a specific biomass and a polymer sample through co-pyrolytic degradation. Therefore, a non-edible food processing waste (cherry seed: CS) and a typical plastic waste (polyvinyl chloride (PVC)) were selected and their interaction was studied using a combined TGA/MS/FT-IR system. By the help of TGA data, the non-isothermal kinetic analysis was performed using four different kinetic methods [Friedman, Flynn-Wall-Ozawa (FWO), Vyazovkin and distributed activation energy (DAEM)]. The kinetic results showed that the activation energy values were in agreement over the conversion degree values between 0.1 and 0.9. For determination of the synergistic or inhibitive interactions, theoretical and experimental thermogravimetry values were also compared. Moreover, in situ determination of the main pyrolytic and co-pyrolytic degradation compounds such as methyl, water, methoxy, hydrogen chloride, carbon dioxide and benzene with respect to temperature and time was studied for the first time. By this way, primary and secondary reactions related to methylation, dehydration, aromatization, fragmentation, dehydrochlorination were interpreted. Consequently, PVC was found to change pyrolytic degradation behaviour of lignocellulosic biomass by changing reactivity, activation energy and reaction mechanisms.

Thermal debinding behavior of a low-toxic DMAA polymer for gelcast ceramic parts based on TG-FTIR and kinetic modeling.

In this work, the pyrolysis characteristics of a low-toxic N,N-dimethylacrylamide (DMAA) gel polymer was investigated through nonisothermal thermogravimetry (TG) and TG-FTIR analyses. Moreover, the thermal debinding kinetics of gelcast SiAlON ceramic parts was studied through three different kinetic models: the Coats–Redfern (C–R) method, distributed activation energy model (DAEM) and three-Gaussian-DAEM-reaction model (3-DAEM). The rationality and adaptability of the three models to the thermal debinding kinetics study were analyzed by comparison with experimental data. The results showed that three mass loss zones were observed in the temperature ranges of 100–320 °C, 320–520 °C and 520–600 °C, respectively, and the main pyrolysis gas products were CO2, H2O and CH4. The conversion rate (α) curves calculated by 3-DAEM were more consistent with the experimental values than those calculated with the C–R and DAEM methods. The fitting quality parameter (Fit%) was less than 2.63%, and the reaction rate (dα/dT) curves calculated by 3-DAEM were bimodal distribution curves, which were in good agreement with the experimental results. The kinetic parameters (E0,i, k0,i and σi) of the global thermal debinding process calculated by 3-DAEM were 116.00–145.79 kJ mol−1, 1.10 × 109 s−1 and 1.67–43.25 kJ mol−1, respectively. It is anticipated that the study achievements can be used to help predict the thermal debinding behavior and design a reasonable debinding technology for the gelcasting of ceramic parts.

Kinetic understanding of the effect of Na and Mg on pyrolytic behavior of lignin using a distributed activation energy model and density functional theory modeling

The catalytic effect of Na and Mg, naturally occurring alkali and alkaline earth metals, on lignin pyrolysis was systematically analyzed using a distributed activation energy model and computational modeling.

Thermal decomposition and combustion characteristics of biomass materials using TG/DTG at different high heating rates and sizes in the air

Thermogravimetric (TGA) analysis was used to study the thermal decomposition and oxidation, combustion characteristics, and kinetics of cotton stalks and sugarcane bagasse powder of various particle sizes under air from room temperature to 1000 °C at heating rates 25, 50, and 75 °C/min. It was observed that all the samples followed a two‐stage reaction mechanism between 200 and 1000 °C clearly indicating regions of volatile oxidation and char combustion during thermal decomposition and oxidation. It was also found that heating rate, particle size, lignocellulosic composition, and gas flow types affect the thermal decomposition mechanism and kinetic parameter values of both materials. The kinetic parameters were determined using simple Distributed Activation Energy Model (DAEM) and three methods of model‐free kinetics. It was found that average activation energy (Eav) for cotton stalks and bagasse for both bulk and different particle sizes ranged between 34–118 kJ/mol and 87–187 kJ/mol, respectively. Results also showed that the values of kinetic parameters obtained from all methods are in a good agreement and can be successfully used to understand the degradation mechanism of solid‐state reaction of these biomass materials. Finally, a comparison between the thermal pyrolysis characteristics of both materials under inert (nitrogen) and air at a heating rate of 10 °C/min is presented and discussed. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13124, 2019

Kinetic analysis and modeling of coal pyrolysis with model-free methods

Knowledge about the rate of coal pyrolysis is of great importance because it exerts remarkable effect on its thermal conversions such as combustion, gasification and liquefaction. Different approaches can be used to obtain the kinetics of coal pyrolysis, the simplest are empirical and global kinetics, where Arrhenius expression is used to correlate the mass loss with temperature. This work conducted pyrolysis of a lignite and a bituminite at various heating rates with a thermo-gravimetric analyzer (TGA). Thermogravimetry coupled with mass spectroscopy (TG-MS), solid state 13C Cross Polarization/ Magic Angle Spinning nuclear magnetic resonance (13C CP/MAS NMR) and Raman analyses were also conducted to correlate the structural characteristics and pyrolysis behavior of the coals. Kinetic analysis was performed by using three model-free methods including Distributed Activation Energy model (DAEM), Ozawa-Flynn-Wall (OFW) and Friedman method. Kinetic modeling was also performed based on the DAEM model with multiple Gaussian sub-distributions of activation energy. The results show that DAEM, OFW and Friedman methods are almost equally effective for analyzing activation energy, which gradually increases with the extent of pyrolysis. Pyrolysis of both the coals can be divided into three stages corresponding to the reactions of various covalent bonds. Three-Gaussian distributed activation energy model (DAEM-G3) is applicable to describing pyrolysis of both coals. The well-matched modeling results with the experimental data over the entire temperature range indicate the validity of DAEM-G3 model in studying and understanding the reaction mechanism of coal pyrolysis.

Thermogravimetric analysis of bamboo-tar under different heating rates based on distributed activation energy model

Carbon fiber is a kind of new polymer material with excellent mechanical properties and being applied widely. The process of carbon fiber prepared by bamboo tar, including extraction, condensation, spinning, oxidation and carbonation, is influenced by the pyrolysis kinetics significantly. In this paper, the thermogravimetric analysis (TGA) of bamboo tar produced in the process of pyrolysis and gasification of the bamboo which is known as Phylostachys sulphurea, was analyzed by the distributed activation energy model (DAEM) to understand the kinetic properties and parameters of bamboo tar. The thermogravimetric analysis of bamboo tar which is used as the raw material of carbon fiber was conducted under 5 different heating rates (i.e. 5, 10, 15, 30 and 50 °C/min, etc.) in nitrogen atmosphere. The results show that the activation energy of bamboo tar and the exponential factor increased significantly with the increase of the heating rate, and the low heating rate is advantageous to the extraction of bamboo tar solvent and the thermal polycondensation, which can provide scientific reference for the optimization of carbon fiber technology. The thermal weight results show that the temperature range of bamboo tar being decomposed rapidly is 213°C-410°C. The ranges of the activation energy were calculated by DAEM, which have small difference in comparisons with five heating rates when the conversion rate is at 0.1-0.6 and the average value of the activation energy is 119 kJ/mol. The stability range of the activation energy is enlarged when the conversion rate is greater than 0.6 and heating rate increases. Keywords: bamboo tar, carbon fiber, thermogravimetric analysis (TGA), distributed activation energy model (DAEM) DOI: 10.25165/j.ijabe.20181106.3839 Citation: Zhang H, Yan B B, Lei T Z, Liu T, Hu J J, Li Y M, et al. Thermogravimetric analysis of bamboo-tar under different heating rates based on distributed activation energy model. Int J Agric & Biol Eng, 2018; 11(6): 180–186.

Kinetics, thermodynamics, gas evolution and empirical optimization of cattle manure combustion in air and oxy-fuel atmospheres

Thermogravimetric (TG) and TG-Fourier transform infrared (FTIR) analyses were performed to quantify the comparative performances of cattle manure combustion in air (N2/O2) and oxy-fuel (CO2/O2) atmospheres at four heating rates. Out of the distributed activation energy model, Flynn-Wall-Ozawa (FWO), Friedman and Starink methods (R2 ≥ 0.86), the FWO method on average led to the highest R2 value with the lowest activation energy. On average, the combustion in the oxy-fuel atmosphere had the lowest activation energy (180.6 kJ/mol) with the highest R2 value (0.9812). Our TG-FTIR results showed that CO2 was the major gas evolution of the cattle manure combustion. Interaction effects of atmosphere type by heating rate on the multiple responses of remaining mass, derivative TG, and differential scanning calorimetry were found to be significant (p < 0.001). The joint optimization of the three responses was achieved at 424.6 °C in the air atmosphere at the heating rate of 40 K/min.

Influence of particle size on combustion behavior of bamboo char used for blast furnace injection

The combustion behavior of bamboo char and its relationship with particle sizes were evaluated using thermo-gravimetric analysis. The results showed that the combustion properties of bamboo char were much better than those of the anthracite used as a coal injected for blast furnace ironmaking due to its porous structure, disordered microcrystalline and higher catalytic index of ash minerals. When the particle size increased from − 0.074 to 0.500–1.000 mm, the ignition temperature and burnout temperature of bamboo char increased, while the combustible index and comprehensive combustion characteristic index decreased slightly. The apparent activation energies of non-isothermal combustion of bamboo char and anthracite were calculated based on the distributed activation energy model. The results showed that the average activation energy was 162.86 kJ/mol for − 0.074 mm anthracite, while it ranged from 71.01 to 89.44 kJ/mol for bamboo chars of different sizes. It revealed that the combustion reactivity of bamboo char in the largest size (0.500–1.000 mm) was much better than that of − 0.074 mm anthracite; thus, the size of biomass char could be enlarged to the maximum size specified by the injection application of blast furnace.