scholarly journals Determining Preexponential Factor in Model-Free Kinetic Methods: How and Why?

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3077
Author(s):  
Sergey Vyazovkin
Keyword(s):  
Activation Energy ◽  
Kinetic Analysis ◽  
Rate Constant ◽  
Condensed Phase ◽  
Compensation Effect ◽  
Preexponential Factor ◽  
Isoconversional Methods ◽  
Activation Entropy ◽  
Model Free ◽  
Kinetics Of

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.

MODEL FREE KINETICS ANALYSIS OF IMPERATA CYLINDRICA (LALANG)

2016 ◽  
Vol 78 (8-3) ◽  
Author(s):  
Olagoke Oladokun ◽  
Arshad Ahmad ◽  
Tuan Amran Tuan Abdullah ◽  
Bemgba Bevan Nyakuma ◽  
Syie Luing Wong
Keyword(s):  
Activation Energy ◽  
Biomass Conversion ◽  
Frequency Factor ◽  
Isoconversional Methods ◽  
Green Energy ◽  
Imperata Cylindrica ◽  
Heating Rates ◽  
Model Free ◽  
Solid Biofuel ◽  
Kinetics Of

This study is the first attempt at investigating the solid state decomposition and the devolatilization kinetics of Imperata cylindrica (lalang) grass termed the “farmer’s nightmare weed” as a potential solid biofuel of the future. Biomass conversion technologies such as pyrolysis and gasification can be utilized for future green energy needs. However an important step in the efficient utilization and process optimizing of biomass conversion processes is understanding the thermal decomposition kinetics of the feedstock. Consequently, thermogravimetric analysis (TGA) of Imperata cylindrica was carried out in the temperature range of 30-1000 °C at four heating rates of 5, 10, 15, and 20 K min-1 using Nitrogen at a flow rate of 20 L min-1 as purge gas. Using the TGA results, the kinetic parameters activation energy (Ea) and pre-exponential frequency factor (ko) of the grass were estimated via the model free or isoconversional methods of Kissinger and Starink. The results obtained for Kissinger model were 151.36 kJ moI-1 and 5.83 x 109 min-1 for activation energy and pre-exponential frequency factor respectively. However, Starink model activation energy and pre-exponential frequency factor were a function of conversion (α) with average values of 159.93 kJ mol-1 and 6.33 x 1022 min-1 respectively. 

Decomposition Kinetics of Switchgrass: Estimating Activation Energy

2014 ◽  
Vol 881-883 ◽  
pp. 726-733
Author(s):  
Gui Ying Xu ◽  
Jiang Bo Wang ◽  
Ling Ping Guo ◽  
Guo Gang Sun
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Apparent Activation Energy ◽  
High Purity ◽  
Isoconversional Methods ◽  
Decomposition Kinetics ◽  
Heating Rates ◽  
Model Free ◽  
Chemical Utilization ◽  
Kinetics Of

TG analysis was used to investigate the thermal decomposition of switchgrass, which is a potential gasification feedstock. 10 mg switchgrass sample with the particles between 0.45 and 0.70 mm was linearly heated to 873 K at heating rates of 10, 20, 30 K/min, respectively, under high-purity nitrogen. The Kissinger method and three isoconversional methods including Friedman, Flynn-wall-Ozawa, Vyazovkin and Lenikeocink methods were used to estimate the apparent activation energy of switchgrass. With the three isoconversional methods, it can be concluded that the activation energy increases with increasing conversion. The four model free methods reveal activation energies in the range of 70-460 kJ/mol. These activation energy values provide the basic data for the thermo-chemical utilization of the switchgrass.

Kinetic Analysis of Alkaline Extraction on Sweet-Bamboo Leaves

2011 ◽  
Vol 332-334 ◽  
pp. 467-470
Author(s):  
Porntip Sae Be ◽  
Suesat Jantip ◽  
Sirisin Chum Rum
Keyword(s):  
Activation Energy ◽  
Kinetic Analysis ◽  
Rate Constant ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Extraction Temperature ◽  
Alkaline Extraction ◽  
K Value ◽  
Bamboo Leaves ◽  
Kinetics Of

This study aimed to investigate the influence of NaOH concentration and temperature used for cellulose extraction from sweet-bamboo leaves on the kinetics of the extraction reaction. The NaOH concentration and the temperature used for the extraction were varied and their effect was examined. It was found that the extraction rate was accelerated by either the increase of NaOH concentration or extraction temperature. The NaOH concentration affected the reaction rate constant, k, and the activation energy, E and the order of the reaction, n. Increase of NaOH concentration enhanced the reaction to move forwards, thus reducing the k and E values of the reaction and the order of the reaction, n, was changed. The correlation of the temperature and the NaOH concentration with the k value showed that at the lower NaOH concentration, the temperature influenced on the k value more significantly. The influence of the NaOH concentration on the k value was lessened with increase of the extraction temperature.

scholarly journals Dynamic Model-Free and Model-Fitting Kinetic Analysis during Torrefaction of Oil Palm Frond Pellets

2020 ◽  
Vol 15 (1) ◽  
pp. 253-263
Author(s):  
Sharmeela Matali ◽  
Norazah Abd Rahman ◽  
Siti Shawalliah Idris ◽  
Nurhafizah Yaacob
Keyword(s):  
Activation Energy ◽  
Thermal Degradation ◽  
Oil Palm ◽  
Model Fitting ◽  
Integral Model ◽  
Model Free ◽  
Solid Biofuel ◽  
Oil Palm Frond ◽  
Kinetics Of ◽  
Palm Frond

Torrefaction is a thermal conversion method extensively used for improving the properties of biomass. Usually this process is conducted within a temperature range of 200-300 °C under an inert atmosphere with residence time up to 60 minutes. This work aimed to study the kinetic of thermal degradation of oil palm frond pellet (OPFP) as solid biofuel for bioenergy production. The kinetics of OPFP during torrefaction was studied using frequently used iso-conversional model fitting (Coats-Redfern (CR)) and integral model-free (Kissinger-Akahira-Sunose (KAS)) methods in order to provide effective apparent activation energy as a function of conversion. The thermal degradation experiments were conducted at four heating rates of 5, 10, 15, and 20 °C/min in a thermogravimetric analyzer (TGA) under non-oxidative atmosphere. The results revealed that thermal decomposition kinetics of OPFP during torrefaction is significantly influenced by the severity of torrefaction temperature. Via Coats-Redfern method, torrefaction degradation reaction mechanism follows that of reaction order with n = 1. The activation energy values were 239.03 kJ/mol and 109.28 kJ/mol based on KAS and CR models, respectively. Copyright © 2020 BCREC Group. All rights reserved 

scholarly journals Kinetic Analysis of the Thermal Degradation of Recycled Acrylonitrile-Butadiene-Styrene by non-Isothermal Thermogravimetry

Polymers ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 281 ◽  
Author(s):  
Rafael Balart ◽  
David Garcia-Sanoguera ◽  
Luis Quiles-Carrillo ◽  
Nestor Montanes ◽  
Sergio Torres-Giner
Keyword(s):  
Thermal Degradation ◽  
Kinetic Analysis ◽  
Acrylonitrile Butadiene Styrene ◽  
Isoconversional Methods ◽  
Reaction Model ◽  
Integral Model ◽  
Heating Rates ◽  
Exponential Factor ◽  
Model Free ◽  
Butadiene Styrene

This work presents an in-depth kinetic study of the thermal degradation of recycled acrylonitrile-butadiene-styrene (ABS) polymer. Non-isothermal thermogravimetric analysis (TGA) data in nitrogen atmosphere at different heating rates comprised between 2 and 30 K min−1 were used to obtain the apparent activation energy (Ea) of the thermal degradation process of ABS by isoconversional (differential and integral) model-free methods. Among others, the differential Friedman method was used. Regarding integral methods, several methods with different approximations of the temperature integral were used, which gave different accuracies in Ea. In particular, the Flynn-Wall-Ozawa (FWO), the Kissinger-Akahira-Sunose (KAS), and the Starink methods were used. The results obtained by these methods were compared to the Kissinger method based on peak temperature (Tm) measurements at the maximum degradation rate. Combined Kinetic Analysis (CKA) was also carried out by using a modified expression derived from the general Sestak-Berggren equation with excellent results compared with the previous methods. Isoconversional methods revealed negligible variation of Ea with the conversion. Furthermore, the reaction model was assessed by calculating the characteristic and functions and comparing them with some master plots, resulting in a nth order reaction model with n = 1.4950, which allowed calculating the pre-exponential factor (A) of the Arrhenius constant. The results showed that Ea of the thermal degradation of ABS was 163.3 kJ mol−1, while ln A was 27.5410 (A in min−1). The predicted values obtained by integration of the general kinetic expression with the calculated kinetic triplet were in full agreement with the experimental data, thus giving evidence of the accuracy of the obtained kinetic parameters.

scholarly journals Analysis of the Kinetics of Swimming Pool Water Reaction in Analytical Device Reproducing Its Circulation on a Small Scale

Sensors ◽  
2020 ◽  
Vol 20 (17) ◽  
pp. 4820 ◽  
Author(s):  
Wojciech Kaczmarek ◽  
Jarosław Panasiuk ◽  
Szymon Borys ◽  
Aneta Pobudkowska ◽  
Mikołaj Majsterek
Keyword(s):  
Activation Energy ◽  
Water Quality ◽  
Rate Constant ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Small Scale ◽  
Pool Water ◽  
Swimming Pool Water ◽  
Kinetics Of ◽  
Analytical Device

The most common cause of diseases in swimming pools is the lack of sanitary control of water quality; water may contain microbiological and chemical contaminants. Among the people most at risk of infection are children, pregnant women, and immunocompromised people. The origin of the problem is a need to develop a system that can predict the formation of chlorine water disinfection by-products, such as trihalomethanes (THMs). THMs are volatile organic compounds from the group of alkyl halides, carcinogenic, mutagenic, teratogenic, and bioaccumulating. Long-term exposure, even to low concentrations of THM in water and air, may result in damage to the liver, kidneys, thyroid gland, or nervous system. This article focuses on analysis of the kinetics of swimming pool water reaction in analytical device reproducing its circulation on a small scale. The designed and constructed analytical device is based on the SIMATIC S7-1200 PLC driver of SIEMENS Company. The HMI KPT panel of SIEMENS Company enables monitoring the process and control individual elements of device. Value of the reaction rate constant of free chlorine decomposition gives us qualitative information about water quality, it is also strictly connected to the kinetics of the reaction. Based on the experiment results, the value of reaction rate constant was determined as a linear change of the natural logarithm of free chlorine concentration over time. The experimental value of activation energy based on the directional coefficient is equal to 76.0 [kJ×mol−1]. These results indicate that changing water temperature does not cause any changes in the reaction rate, while it still affects the value of the reaction rate constant. Using the analytical device, it is possible to constantly monitor the values of reaction rate constant and activation energy, which can be used to develop a new way to assess pool water quality.

In Situ FT-IR Studies on the Amine-Catalyzed Urethane Reaction Kinetics of 1,3-Butanediol

2012 ◽  
Vol 472-475 ◽  
pp. 2223-2226
Author(s):  
Peng Fei Yang
Keyword(s):  
Rate Constant ◽  
Phenyl Isocyanate ◽  
Hydroxyl Group ◽  
Activation Entropy ◽  
Ir Studies ◽  
Initial Stage ◽  
Different Temperatures ◽  
Ft Ir ◽  
Kinetics Of

Phenyl isocyanate is used to react with 1,3-butanediol at different temperatures. Toluene is used as solvent and 1,4-diazabicyclo[2,2,2]octane is used as catalyst. In-situ FT-IR is used to monitor the reaction to work out rate constant, Arrhenius equation and Eyring equation. The urethane reaction has been found to be a second order reaction, and the rate constant seems different between initial stage and final stage. The activation energy (Ea), activation enthalpy (ΔH) and activation entropy (ΔS) for the urethane reaction of primary hydroxyl group are calculated out, which are 26.4 kJ•mol-1, 23.6 kJ•mol-1and -186.6 J•mol-1•k-1, respectively. They are very useful to reveal the reaction mechanism.

scholarly journals The combination of carbon monoxide–haem with apoperoxidase

1969 ◽  
Vol 114 (4) ◽  
pp. 719-724 ◽  
Author(s):  
Charles Phelps ◽  
Eraldo Antonini
Keyword(s):  
Activation Energy ◽  
Carbon Monoxide ◽  
Rate Constant ◽  
Binding Sites ◽  
Order Process ◽  
First Order ◽  
Effects Of Ph ◽  
Kinetics Of

1. Static titrations reveal an exact stoicheiometry between various haem derivatives and apoperoxidase prepared from one isoenzyme of the horseradish enzyme. 2. Carbon monoxide–protohaem reacts rapidly with apoperoxidase and the kinetics can be accounted for by a mechanism already applied to the reaction of carbon monoxide–haem derivatives with apomyoglobin and apohaemoglobin. 3. According to this mechanism a complex is formed first whose combination and dissociation velocity constants are 5×108m−1sec.−1 and 103sec.−1 at pH9·1 and 20°. The complex is converted into carbon monoxide–haemoprotein in a first-order process with a rate constant of 235sec.−1 for peroxidase and 364sec.−1 for myoglobin at pH9·1 and 20°. 4. The effects of pH and temperature were examined. The activation energy for the process of complex-isomerization is about 13kcal./mole. 5. The similarity in the kinetics of the reactions of carbon monoxide–haem with apoperoxidase and with apomyoglobin suggests structural similarities at the haem-binding sites of the two proteins.

THE REACTION BETWEEN CYANATE AND HYPOCHLORITE

1956 ◽  
Vol 34 (4) ◽  
pp. 489-501 ◽  
Author(s):  
M. W. Lister
Keyword(s):  
Activation Energy ◽  
Ionic Strength ◽  
Rate Constant ◽  
Hypochlorous Acid ◽  
Effect Of Temperature ◽  
Slow Step ◽  
True Activation Energy ◽  
Rate Of Reaction ◽  
Different Temperatures ◽  
Kinetics Of

The reaction between sodium hypochlorite and potassium cyanate in the presence of sodium hydroxide has been examined. The main products are chloride, and carbonate ions and nitrogen; but, especially if much hypochlorite is present, some nitrate is formed as well. The rate of reaction is proportional to the cyanate and hypochlorite concentrations, but inversely proportional to the hydroxide concentration: the rate constant is 5.45 × 10−4 min.−1 at 65 °C, at an ionic strength of 2.2. The rate constant increases somewhat as the ionic strength rises from 1.7 to 3.5. The effect of temperature makes the apparent activation energy 25 kcal./gm-molecule. The kinetics of the reaction suggest that the slow step is really a reaction of hypochlorous acid and cyanate ions, and possible intermediate products of this reaction are suggested. Allowing for the different extent of hydrolysis of hypochlorite at different temperatures, the true activation energy is found to be 15 kcal./gm-mol., which is consistent with the observed rate of reaction.

Correlation analysis of reactivity in the addition of substituted benzylamines to β-nitrostyrene

1996 ◽  
Vol 74 (4) ◽  
pp. 625-629 ◽  
Author(s):  
Neeta Jalani ◽  
Seema Kothari ◽  
Kalyan K. Banerji
Keyword(s):  
Activation Energy ◽  
Correlation Analysis ◽  
Rate Constant ◽  
Steric Hindrance ◽  
Nucleophilic Addition ◽  
Regression Coefficients ◽  
Nucleophilic Attack ◽  
Arrhenius Activation Energy ◽  
First Order ◽  
Kinetics Of

The kinetics of addition of a number of ortho-, meta-, and para-substituted benzylamines to β-nitrostyrene (NS) in acetonitrile have been studied. The reaction is first order with respect to NS. The order with respect to the amine is higher than one. It has been shown that the reaction follows two mechanistic pathways, uncatalyzed and catalyzed by the amine. The Arrhenius activation energy for the catalyzed path is negative, indicating the presence of a pre-equilibrium (k1, k−1) leading to the formation of a zwitterion. The values of the rate constant, k1, for the nucleophilic attack have been determined for 28 benzylamines. The rate constant k1 was subjected to correlation analysis using Charton's LDR and LDRS equations. The polar regression coefficients are negative, indicating the formation of a cationic species in the transition state. The reaction is subject to steric hindrance by ortho substituents. Key words: nucleophilic addition, benzylamines, correlation analysis, kinetics, alkene.

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