Frequency Factor K0 Research Articles

Interfacial characteristics and thermal stability of polymer-derived SiCf/Ti composite fabricated by powder hot isostatic pressing

The novel SiCf/Ti composite is prepared by hot isostatic pressing (HIP) with polymer-derived (PD) SiC fiber and powder titanium alloy as raw materials in this work. The interfacial characteristics and thermal stability of the PD SiCf/Ti composite have been systematically investigated. The interfacial properties of the PD SiCf/Ti composites are quantified to discuss the interfacial reaction mechanisms and kinetics. The results show that with the proposed HIP process, the powder matrix can be near-fully dense, and the matrix and SiC fiber are well bonded with a uniform interfacial layer. The major interfacial products are C-Ti compounds and Si-Ti compounds, which are formed by atomic diffusion reaction. During subsequent thermal exposure conditions, the interfacial layer growth is temperature-dependent and diffusion-controlled, following the parabolic relation and Arrhenius law. The frequency factor k0 is 102–103 times lower than that in the chemical vapor deposition (CVD) SiCf/Ti composites, showing better interfacial thermal stability. After thermal exposure, the element diffusion becomes significant, and the microhardness of the near-interface zone is noticeably greater than the matrix microhardness because of the atomic diffusion of C. The microhardness of both the matrix and near-interface zone reaches the highest value after 900 °C/9 h thermal exposure. It is concluded that the PD SiCf/Ti composites with good thermal stability can be successfully fabricated by powder HIP.

Physical characterization and crystallization kinetics of amorphous BiSe chalcogenide glasses

The influence of Bi concentration on the thermal parameters viz temperatures of glass transition (Tgl) and crystallization (Tpc) of binary BixSe100-x glasses were studied experimentally. The activation energy of glass transition (EGl) has been estimated as the averaged value deduced based on Kissenger's relationship and its approximation. On the other hand, Afify and Aly methods help one to estimate the crystallization activation energy (Epc), the frequency factor (k0) and the order of reaction (n) with no approximation. The observed increase in EGl and Epc values resulted from increasing both Tgl and Tpc with increasing of the Bi content. The Lasocka relationship can describe the heating rate dependence of Tgl and Tpc. A good correlation between Tgl and Tpc was investigated. The attained results were discussed according to the distribution of the chemical bonds, the main coordination number (Nr), average heats of atomization (Hs), the mean bond energy (Es), the cohesive energy (CE), and the overall average bond energy (<E>) for BixSe100-x glasses.

Experimental study of hydrogen generation from in-situ heavy oil gasification

Heavy oil in-situ gasification technology (ISG) produces hydrogen by injecting air and water into the formation and chemically react with the heavy oil, which can efficiently exploit oil and gas resources in the form of clean energy. The pyrolysis reaction of crude oil is particularly important for this technology regarding hydrogen generation. In this research, the mechanisms of hydrogen generation from heavy oil pyrolysis were investigated based on the thermogravimetric analyzer (TGA) and mass spectrometer (MS). The experimental results show that the weight loss of heavy oil under 25–900 °C can be divided into two stages. The first stage is mainly the evaporation of light fractions, which corresponds to the physical stage. The second stage contains pyrolysis and coke dehydrogenation reactions, which is considered as the chemical stage. Also, the study indicates that the hydrogen generation occurs in both pyrolysis and coke dehydrogenation reactions, and 80% of hydrogen is generated from the coke dehydrogenation reaction with corresponding reaction temperature range of 528–820 °C. Furthermore, the kinetic parameters of heavy oil pyrolysis were obtained based on the distributed activation energy model (DAEM), where the apparent activation energy of the coke dehydrogenation reaction is greater than 350 kJ/mol, and the reaction frequency factor (k0) is greater than 2.83 × 1023 s−1. The reaction kinetic parameters obtained in this paper and the established law of hydrogen generation by heavy oil under thermal effect lay the foundation for further research on ISG technology.

Formation kinetics of polycyclic aromatic hydrocarbons (PAHs) during drying process of olive pomace

The objective of this study was to evaluate the formation kinetics of polycyclic aromatic hydrocarbons (PAHs) during drying of olive pomace. It was dried at 170, 200 and 230 °C until the final moisture of 5%. PAH analyses were realized after certain drying times and moisture contents. Kinetics of the total PAH formation was comprised with the formation of PAH compounds through the drying process. The highest formation (2224 µg/kg) was observed at 200 °C and 5% moisture after 40 min. This also indicated the significance of drying time and evolution of temperature on the formation of PAH compounds. First order kinetic was applied to determine the kinetic constants as a function of temperature. Total PAH fomration rate constants (k) increased with the drying temperature. Activation energy (Ea) and frequency factor (k0) values were determined to be 45.9 × 103 kJ/kg-mol and 18125.95 min−1, respectively using the Arrhenius equation.

Microreactor technology for synthesis of ethyl methyl oxalate from diethyl oxalate with methanol and its kinectics

AbstractThis study focused on the performances and kinetics of the transesterification reaction of diethyl oxalate with methanol to prepare ethyl methyl oxalate via microreactor technology. The conversion of 79.8% of diethyl oxalate (DEO) and the selectivity of 65.9% of ethyl methyl oxalate (EMO) was obtained under the following optimized conditions: the mole ratio of methanol to diethyl oxalate was 3.3:1, the temperature was 35°C, the K2CO3 catalyst concentration was 15 mg/mL, and the residence time was 2.30 minutes. In the temperature range of 25°C to 38°C, the simplified dynamic model was found to obtain the reaction order (α = 2.30), frequency factor (k0 = 2.377 × 105), and apparent activation energy (E = 31.86 kJ/mol). The macroscopic dynamic equation was derived from the experimental result of the transesterification reaction of two feedstocks, which can be obtained through a series of calculations.

Kinetic modeling of cottonseed oil transesterification with ethanol

This study aimed to evaluate the kinetic behavior of cottonseed oil transesterification with ethanol based on a pseudo first order kinetic model. A 23 factorial planning with three central points was performed by considering temperature, catalyst concentration and alcohol/oil molar ratio as dependent variables and biodiesel concentration as response signal. It was observed that the highest conversion was obtained for the following conditions: temperature between 50 and 70 °C, high alcohol/oil molar ratio and low percentage of catalyst. All samples were collected during time intervals of 5–10–15–30–60 and 90 min. A set of kinetic constant values were obtained for each operating condition ranging from 72 to 23l min−1. Indeed, it was possible to obtain the kinetic parameters frequency factor k0 = 5807.05 dm3*mol−1*min−1 and Ea = 16.84 kJ*mol−1 for biodiesel production with ethanol.

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.

Pyrolysis of tobacco factory waste biomass

Tobacco waste is one of the main industrial agricultural wastes. In this study, potential of pyrolysis process for valorization of this type of biomass waste was investigated based on thermogravimetirc analysis. Thermogravimetric analysis of the tobacco waste material was carried out at different heating rates (5, 10, 20, 40 °C min−1) by heating from room temperature to 900 °C in an inert nitrogen atmosphere. The main decomposition occurred approximately between temperatures 150 and 390 °C. Pyrolysis kinetic was investigated by the DAEM method to determine kinetic parameters (activation energy and frequency factor) by using thermogravimetric data. Activation energy (E) and the frequency factor (k0) were ranging from 280.38 to 201.96 kJ mol−1 and 2.45E+14 to 8.19E+25 s−1, respectively. The evolved gaseous products were investigated by using the TG-FTIR technique, and effect of temperature and heating rate on products was examined. Characterization of the bio-oil obtained from pyrolysis of the tobacco waste in the fixed-bed reactor was carried out using FT-IR, GC–MS and 1H-NMR techniques. According to GC–MS results, bio-oil consists mainly of nicotine (26.78%), phenol (8.02%) and limonene (4.59%) compounds. GC–MS, FT-IR and 1H-NMR results were consistent with each other.

Heat treatment and kinetics of precipitation of β-Mg17Al12 phase in AZ91 alloy

Abstract This study investigated the effect of aging on the precipitation and kinetics of second phase Mg17Al12 in AZ91 magnesium alloy (Mg-9 wt% Al-1 wt% Zn), using X-ray diffraction, microhardness measurements and differential scanning calorimetric analysis (DSC). With the last instrument, the all samples were heated from room temperature to 400 °C, at heating rates of 10–30 °C/min. The results were supplemented by measuring the average of activation energies, using isothermal treatments by Johnson–Mehl–Avrami (JMA) methods and by non-isothermal treatments using Ozawa, Boswell, Kissinger, Mahadevan, Augis and Bennett methods, were around 67.18 and 62.02 kJ/mol. The frequency factor k0 calculated by the isothermal treatment is equal to 1.24 109 s−1. In non-isothermal treatment, the numerical factor m and the Avrami parameter n is estimated to be approximately equal to 3 and 2.79 respectively. This value corresponding that the bulk nucleation with a constant number of nuclei was dominant in three-dimensional (polyhedron) controlled by interface reaction.

Rheometric Non-Isothermal Gelatinization Kinetics of Chickpea Flour-Based Gluten-Free Muffin Batters with Added Biopolymers.

An attempt was made to analyze the elastic modulus (G′) of chickpea flour (CF)-based muffin batters made with CF alone and with added biopolymers (whey protein (WP), xanthan gum (XG), inulin (INL), and their blends) in order to evaluate their suitability to be a wheat flour (WF) substitute in muffins, and to model the heat-induced gelatinization of batters under non-isothermal heating condition from 25 °C to 90 °C. A rheological approach is proposed to determine the kinetic parameters (reaction order (n), frequency factor (k0), and activation energy (Ea)) using linearly-increasing temperature. Zero-order reaction kinetics adequately described batter gelatinization process, therefore assuming a constant rate independent of the initial G′ value. The change of the derivative of G′ with respect to time (dG′/dt) versus temperature is described by one exponential function with activation energies ranging from 118 to 180 kJ·mol−1. Control wheat gluten batter, with higher and lower starch and protein contents, respectively, than CF-based batters, exhibited the highest Ea value. Formulation of CF-based gluten-free batters with starch and protein contents closer to the levels of WF-based batter could be a strategy to decrease differences in kinetic parameters of muffin batters and, therefore, in technological characteristics of baked muffins.

Calculation of Activation Energy, Frequency Factor and Avrami Exponent of Amorphous Fe76Pr4B20 and Fe76Dy4B20 Alloys on the Basis of Crystallization Kinetics

The activation energy of crystallization (Ea), Frequency factor(k0) and Avrami exponent (n) of amorphous Fe76Pr4B20 and Fe76Dy4B20 alloys have been calculated by three methods namely Kissinger, Augis- Bennet and Matusita-Sakka on the basis of crystallization kinetics using Differential Scanning Calorimetry (DSC). The average activation energy for primary crystallization of amorphous Fe76Pr4B20 and Fe76Dy4B20 alloys using the above three methods is determined as 389.67 kJouls/ mole and 578.59 kJouls/mole, respectively. The frequency factor of amorphous Fe76Pr4B20 and Fe76Dy4B20 alloys using Kissinger method is found to be 4.542 × 1019 (sec)-1 and 8.5 × 1031 (sec)-1, respectively. Similarly, the Avrami exponent of amorphous Fe76Pr4B20 and Fe76Dy4B20 alloys is found to be 1.67 and 0.831, respectively.

Catalytic pyrolysis characteristics of scrap printed circuit boards by TG-FTIR

In the present work, pyrolysis and catalytic pyrolysis of waste printed circuit boards (WPCBs) was carried out in the coupling of Thermo Gravimetric Analysis and Fourier Transform Infrared Spectroscopy (TG-FTIR) under nitrogen atmosphere. The reaction temperature was increased from 30 to 700°C, while the heating rates were varied from 10 to 40°C/min. Experimental results show that the effect of catalyst on the WPCBs particles pyrolysis was significance. Compared with another two combustion-supporting agents (MgO, CaO), the whole pyrolysis process was optimized when the catalyst ZSM-5 was added into the WPCBs particles. The distributed activation energy model (DAEM) was used to analyze the kinetic parameters of the WPCBs pyrolysis. It was found that values of frequency factor (k0) changed with different activation energy (E) values during pyrolysis process. The activation energy values range from 129.15 to 280.53kJ/mol, and the frequency factor values range from 9.02×1010 to 4.21×1022s−1. The generated major products for the catalytic pyrolysis of WPCBs were H2, CO2, CO, H2O, phenols and aromatics.

Thermal stability and glass forming ability of amorphous Hf2Co11B alloy

Crystallization kinetics and crystalline structure of melt-spun fully amorphous Hf2Co11B alloys in as-quenched state and after annealing were investigated. Differential scanning calorimetry measurements in isochronal mode were performed with different heating rates q to characterize crystallization process. Three exothermal peaks occur during heating, with maxima at 868K, 888K and 926K (heating rate q=20K/min). Kissinger, Ozawa and Augis-Bennett models were used for the activation energy calculations. All three methods give similar values of Ea within experiment inaccuracy and its average value is equal to 343±15kJ/mol for the first, 468±40kJ/mol for the second and 435±5kJ/mol for the third crystallization peak. Additionally, frequency factor k0 values were determined using Augis-Bennett model to be of order of 1017–1024s−1. At the beginning of the first crystallization event nucleation and grain growth is three-dimensional and changes to one-dimensional at the end of the process. The semi-empirical Miedema's model was applied to calculate glass forming ability of the Hf2Co11B alloy. Formation enthalpy of amorphous phase is equal to −20.6kJ/mol, what fits in with rather moderate possibility of formation of amorphous phase using rapid quenching technique.

Isoconversional Methods for Kinetic Modeling of Kerogen Pyrolysis Using TG Data

The pyrolysis kinetics of the Jordanian Lajjun oil shale kerogen was investigated inside a TGA reactor. Kerogen samples (extracted by mineral digestion) were non-isothermally heated at rates varying from 1 to 50°C/min under 350-550C in N2 atmosphere. Friedman, Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) models were employed to estimate the kinetic parameters at isoconversional points ranging from 0.1 to 0.9. The value of the calculated apparent activation energy (E) was found to vary with both the employed model and the conversion (x). Using the three models, the calculated increased with from 10 to 30% (low level), and then decreased with from 30 to 60% (medium level). At high level (60 to 90%), however, increased with increase using both KAS and FWO models, while it continuously dropped with increase using Friedman model. The frequency factor (k0) calculated form each model was found to linearly correlate with E. Compared to KAS and FWO models, Friedman' provided a more accurate fit to the experimental data.

Decolorization of the azo dye Acid Red 18 by crude manganese peroxidase: Effect of system parameters and kinetic study

To optimize operating conditions for the decolorization of the azo dye Acid Red 18 (AR18) by crude manganese peroxidase (MnP), some important factors affecting enzymatic decolorization were systematically investigated. Under the optimal enzyme reaction conditions, a decolorization efficiency of more than 82.3% was achieved after 60 min treatment. Furthermore, the manganese chelators, malate, tartrate, and lactate were found to be more favorable for the decolorization of AR18 than malonate, acetate, succinate, maleate, oxalate, and citrate. However, the presence of NaCl or Na2SO4 had a negative impact on the decolorization of AR18. The Km and Vmax values of MnP for AR18 were 169.66 μmol L− 1 and 20.63 μmol L− 1 min− 1, respectively. The decolorization of AR18 by MnP followed second-order reaction kinetics with respect to the dye concentration. The decolorization rate constant increased with increasing temperature from 20°C to 35°C, which indicated an activation energy (Ea) of 15.87 kcal mol− 1 and frequency factor (k0) of 1.36 × 108 mg− 1 L min− 1 according to the Arrhenius equation. The results obtained provide experimental data for the application of crude MnP for the decolorization of AR18, and help to elucidate the biochemical mechanism of dye decolorization by the enzyme.

Comparison of Browning Colour Formation on the Surface of Fish Samples during Grilling

A comparison of the browning of fish species grilled using far-infrared (FIR) heating was evaluated. Japanese amberjack (Seriola quinqueradiata), Japanese Spanish mackerel (Scomberomorus niphonius), salmon (Oncorhynchus masou), and red sea bream (Pagrus major) were used. Temperature and colour (CIE L*, a*, and b* values) of the sample surface were monitored over time. The rate of L* change was evaluated by treating the browning reaction as a first-order reaction. Colour changes based on a* and b* values were correlated with L* values using empirical equations. During browning, the trajectories of sample colour changes followed almost the same pattern, except for salmon, which was probably due to astaxanthin content. Samples with higher fat content browned faster, according to their higher frequency factor (k0) of the browning rate. An empirical equation for k0 prediction based on sample fat content was obtained, giving fairly good approximations to measured values.

A Kinetic Study of Indium Leaching from Indium-Bearing Zinc Ferrite Under Microwave Heating

To obtain information about leaching reaction and kinetics of indium from indium-bearing materials under microwave heating (MH), leaching of indium from indium-bearing zinc ferrite (IBZF) has been investigated. IBZF samples under MH and under conventional heating (CH) were studied by X-ray diffraction and specific surface area. Compared with that of CH, the effect of MH and the effects of various control parameters on indium leaching were studied. The results showed that compared with CH, MH enhanced the indium leaching from IBZF and increased the leaching rate. The leaching behavior of indium from IBZF was analyzed by unreacted shrinking core model, and the regression of kinetic equations showed that leaching of indium from IBZF obeyed the model very well. The activation energies under MH and under CH were 77.374 kJ/mol and 53.555 kJ/mol, respectively; the ratio of frequency factor K0(MH)/K0(CH) was 10,818.36. The activation mechanism involved in leaching of indium under MH was mainly the increase of reactant energy and effective collision, which caused by the thermal and nonthermal microwave effect. Compared with the activation energy, the effective collision played a more important role in the acceleration of leaching of indium.

Study on the Kinetics of Wet Flue Gas Desulfurization by Carbide Slag

Current industrial desulfurization processes involve in economic costs, if carbide slag can be used in those processes, the costs will be reduced and the goal treating waste with waste can be achieved. A mathematic reaction model was built based on the chemical reaction of desulfurization by carbide slag, the overall reaction order n=α+β=1.74, the activation energy Ea=21749.56173J/mol and the frequency factor k0=0.349533643 .

Simultaneous Thermodynamic and Kinetic Parameters Determination Using Differential Scanning Calorimetry

Problem statement: The determination of reaction kinetics is of major importance, as for industrial reactors optimization as for environmental reasons or energy limitations. Although calorimetry is often used for the determination of thermodynamic parameters alone, the question that arises is: how can we apply the Differential Scanning Calorimetry for the determination of kinetic parameters. The objective of this study consists to proposing an original methodology for the simultaneous determination of thermodynamic and kinetic parameters, using a laboratory scale Differential Scanning Calorimeter (DSC). The method is applied to the dichromate-catalysed hydrogen peroxide decomposition. Approach: The methodology is based on operating of experiments carried out with a Differential Scanning Calorimeter. The interest of this approach proposed is that it requires very small quantities of reactants (about a few grams) to be implemented. The difficulty lies in the fact that, using such microcalorimeters, the reactants temperature cannot directly be measured and a particular calibration procedure has thus to be developed, to determine the media temperature in an indirect way. The proposed methodology for determination of kinetics parameters is based on resolution of the coupled heat and mass balances. Results: A complete kinetic law is proposed. The Arrhenius parameters are determined as frequency factor k0 = 1.39×109 s−1 and activation energy E = 54.9 kJ mol−1. The measured enthalpy of reaction is ΔrH=−94 kJ mol−1. Conclusion: The comparison of the results obtained by such an original methodology with those obtained using a conventional laboratory scale reactor calorimetry, for the kinetics determination of, shows that this new approach is very relevant.

A critical study of the Miura–Maki integral method for the estimation of the kinetic parameters of the distributed activation energy model

Using some theoretically simulated data constructed from known sets of the activation energy distribution f(E) (assumed to follow the Gaussian distribution f(E)=1σ2πexp[-(E-E0)22σ2], where E is the activation energy, E0 is the mean value of the activation energy distribution, and σ is the standard deviation of the activation energy distribution) and the frequency factor k0, a critical study of the use of the Miura–Maki integral method for the estimation of the kinetic parameters of the distributed activation energy model has been performed from three cases. For all cases, the use of the Miura–Maki integral method leads to important errors in the estimation of k0. There are some differences between the assumed and calculated activation energy distributions and the differences decrease with increasing the assumed k0 values (for Case 1), with increasing the assumed σ values (for Case 2), and with decreasing the b values (for Case 3).