scholarly journals Advanced Isoconversional Kinetic Analysis for the Elucidation of Complex Reaction Mechanisms: A New Method for the Identification of Rate-Limiting Steps

Molecules ◽  
2019 ◽  
Vol 24 (9) ◽  
pp. 1683 ◽  
Author(s):  
Nicolas Sbirrazzuoli
Keyword(s):  
Activation Energy ◽  
Kinetic Analysis ◽  
Single Step ◽  
Thermoanalytical Techniques ◽  
Diffusion Controlled ◽  
Physical Transformation ◽  
Exponential Factors ◽  
Isoconversional Kinetic Analysis ◽  
The Individual ◽  
Rate Limiting

Two complex cure mechanisms were simulated. Isoconversional kinetic analysis was applied to the resulting data. The study highlighted correlations between the reaction rate, activation energy dependency, rate constants for the chemically controlled part of the reaction and the diffusion-controlled part, activation energy and pre-exponential factors of the individual steps and change in rate-limiting steps. It was shown how some parameters computed using Friedman’s method can help to identify change in the rate-limiting steps of the overall polymerization mechanism as measured by thermoanalytical techniques. It was concluded that the assumption of the validity of a single-step equation when restricted to a given α value holds for complex reactions. The method is not limited to chemical reactions, but can be applied to any complex chemical or physical transformation.

scholarly journals Synthesis and Polymerization Kinetics of Rigid Tricyanate Ester

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1686
Author(s):  
Andrey Galukhin ◽  
Roman Nosov ◽  
Ilya Nikolaev ◽  
Elena Melnikova ◽  
Daut Islamov ◽  
...  
Keyword(s):  
Kinetic Analysis ◽  
Single Step ◽  
Polymerization Kinetics ◽  
Scanning Calorimetry ◽  
Modulated Differential Scanning Calorimetry ◽  
Diffusion Controlled ◽  
Polymerization Product ◽  
The One ◽  
Kinetics Of

A new rigid tricyanate ester consisting of seven conjugated aromatic units is synthesized, and its structure is confirmed by X-ray analysis. This ester undergoes thermally stimulated polymerization in a liquid state. Conventional and temperature-modulated differential scanning calorimetry techniques are employed to study the polymerization kinetics. A transition of polymerization from a kinetic- to a diffusion-controlled regime is detected. Kinetic analysis is performed by combining isoconversional and model-based computations. It demonstrates that polymerization in the kinetically controlled regime of the present monomer can be described as a quasi-single-step, auto-catalytic, process. The diffusion contribution is parameterized by the Fournier model. Kinetic analysis is complemented by characterization of thermal properties of the corresponding polymerization product by means of thermogravimetric and thermomechanical analyses. Overall, the obtained experimental results are consistent with our hypothesis about the relation between the rigidity and functionality of the cyanate ester monomer, on the one hand, and its reactivity and glass transition temperature of the corresponding polymer, on the other hand.

Full kinetic analysis of a rhodium-catalyzed hydroformylation: beyond the rate-limiting step picture

2015 ◽  
Vol 5 (1) ◽  
pp. 129-133 ◽  
Author(s):  
U. Gellrich ◽  
T. Koslowski ◽  
B. Breit
Keyword(s):  
Steady State ◽  
Kinetic Analysis ◽  
Transition States ◽  
Single Step ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
State Approximation ◽  
Steady State Approximation ◽  
Rate Limiting

A complete dynamic kinetic analysis beyond the steady state approximation of the rhodium-catalyzed hydroformylation with the 6-DPPon ligand is presented. The results show that not one single step but several transition states and intermediates control the selectivity and activity of the catalysis.

Isoconversional Kinetic Analysis of Pyrolysis of Sugarcane Bagasse

2012 ◽  
Vol 727-728 ◽  
pp. 1830-1835 ◽  
Author(s):  
Kássia Graciele dos Santos ◽  
Ricardo A. Malagoni ◽  
Taisa S. Lira ◽  
Valéria V. Murata ◽  
Marcos A.S. Barrozo
Keyword(s):  
Activation Energy ◽  
Kinetic Study ◽  
Kinetic Analysis ◽  
Heating Rate ◽  
Sugarcane Bagasse ◽  
Isoconversional Methods ◽  
The Other ◽  
Isoconversional Kinetic Analysis

This paper presents a kinetic study of pyrolysis of sugarcane bagasse from dynamic thermogravimetric experiments (TG). The methods of Kissinger, Ozawa, Starink, Kissinger-Akahira-Sunose and Friedman were used to estimate the activation energy. These methods consider the temperature shifts with increase of heating rate for a given conversion in dynamic TG tests. The activation energy values obtained by the isoconversional methods were in a range 182.8 192.4 kJ·mol-1, values very close to the other biomasses presented by literature.

scholarly journals Kinetic Analysis of Digestate Slow Pyrolysis with the Application of the Master-Plots Method and Independent Parallel Reactions Scheme

Molecules ◽  
2019 ◽  
Vol 24 (9) ◽  
pp. 1657 ◽  
Author(s):  
Pietro Bartocci ◽  
Roman Tschentscher ◽  
Ruth Elisabeth Stensrød ◽  
Marco Barbanera ◽  
Francesco Fantozzi
Keyword(s):  
Activation Energy ◽  
Kinetic Analysis ◽  
Single Step ◽  
Conversion Degree ◽  
Pyrolysis Process ◽  
Average Value ◽  
Model Free ◽  
Master Plots Method ◽  
Master Plots ◽  
Parallel Reactions

The solid fraction obtained by mechanical separation of digestate from anaerobic digestion plants is an attractive feedstock for the pyrolysis process. Especially in the case of digestate obtained from biogas plants fed with energy crops, this can be considered a lignin rich residue. The aim of this study is to investigate the pyrolytic kinetic characteristics of solid digestate. The Starink model-free method has been used for the kinetic analysis of the pyrolysis process. The average Activation Energy value is about 204.1 kJ/mol, with a standard deviation of 25 kJ/mol, which corresponds to the 12% of the average value. The activation energy decreased along with the conversion degree. The variation range of the activation energy is about 99 kJ/mol, this means that the average value cannot be used to statistically represent the whole reaction. The Master-plots method was used for the determination of the kinetic model, obtaining that n-order was the most probable one. On the other hand, the process cannot be modeled with a single-step reaction. For this reason it has been used an independent parallel reactions scheme to model the complete process.

scholarly journals Acyl-CoA synthetase and the peroxisomal enzymes of β-oxidation in human liver. Quantitative analysis of their subcellular localization

1984 ◽  
Vol 224 (3) ◽  
pp. 709-720 ◽  
Author(s):  
M Bronfman ◽  
N C Inestrosa ◽  
F O Nervi ◽  
F Leighton
Keyword(s):  
Human Liver ◽  
Fatty Acyl ◽  
Single Step ◽  
Synthetase Activity ◽  
Beta Oxidation ◽  
Analysis Of Results ◽  
Fractionation Method ◽  
Hydroxyacyl Coa Dehydrogenase ◽  
Acyl Coa Oxidase ◽  
Rate Limiting

The presence of acyl-CoA synthetase (EC 6.2.1.3) in peroxisomes and the subcellular distribution of beta-oxidation enzymes in human liver were investigated by using a single-step fractionation method of whole liver homogenates in metrizamide continuous density gradients and a novel procedure of computer analysis of results. Peroxisomes were found to contain 16% of the liver palmitoyl-CoA synthetase activity, and 21% and 60% of the enzyme activity was localized in mitochondria and microsomal fractions respectively. Fatty acyl-CoA oxidase was localized exclusively in peroxisomes, confirming previous results. Human liver peroxisomes were found to contribute 13%, 17% and 11% of the liver activities of crotonase, beta-hydroxyacyl-CoA dehydrogenase and thiolase respectively. The absolute activities found in peroxisomes for the enzymes investigated suggest that in human liver fatty acyl-CoA oxidase is the rate-limiting enzyme of the peroxisomal beta-oxidation pathway, when palmitic acid is the substrate.

Isotope Exchange of Gaseous Oxygen with Oxide LaMno3+δ Nanograins Boundary

2010 ◽  
Vol 297-301 ◽  
pp. 1301-1305
Author(s):  
Anatoly Yakovlevich Fishman ◽  
Tatiana Eugenievna Kurennykh ◽  
Vladimir Borisovich Vykhodets ◽  
V.B. Vykhodets
Keyword(s):  
Activation Energy ◽  
Exchange Rate ◽  
Isotope Exchange ◽  
Shock Wave Loading ◽  
Wave Loading ◽  
Gaseous Oxygen ◽  
Exponential Factor ◽  
Significant Difference ◽  
Exponential Factors ◽  
Arrhenius Expression

Isotope exchange of oxygen 18О2 with the boundary of nanograins of oxide LaMnO3+ obtained by the method of shock-wave loading was investigated in the temperature range of 400 – 500 °C. It was established that the temperature dependence of the isotope exchange rate is described by the Arrhenius expression, the activation energy and the pre-exponential factor being 1.67 eV and 1.8∙102 cm/s, respectively. Comparison with literature data has shown that for oxide LaMnO3+, a significant difference in activation energies and pre-exponential factors is observed for the isotope exchange rate with a ‘defect-free’ surface and the nanograin boundary. In case of the boundary, these parameters were higher: the activation energy about two times, and the pre-exponential factor, by almost 7 orders of magnitude.

Kinetic analysis of biomass pyrolysis using a double distributed activation energy model

2015 ◽  
Vol 121 (3) ◽  
pp. 1403-1410 ◽  
Author(s):  
Benedetta de Caprariis ◽  
Maria Laura Santarelli ◽  
Marco Scarsella ◽  
Carlos Herce ◽  
Nicola Verdone ◽  
...  
Keyword(s):  
Activation Energy ◽  
Kinetic Analysis ◽  
Energy Model ◽  
Biomass Pyrolysis ◽  
Distributed Activation Energy Model

scholarly journals Gas-phase detonation propagation in mixture composition gradients

2012 ◽  
Vol 370 (1960) ◽  
pp. 567-596 ◽  
Author(s):  
D. A. Kessler ◽  
V. N. Gamezo ◽  
E. S. Oran
Keyword(s):  
Activation Energy ◽  
Reaction Model ◽  
Single Step ◽  
Mixture Composition ◽  
Composition Gradient ◽  
Detonation Properties ◽  
High Activation ◽  
Zone Structure ◽  
Detonation Cell ◽  
High Activation Energy

The propagation of detonations through several fuel–air mixtures with spatially varying fuel concentrations is examined numerically. The detonations propagate through two-dimensional channels, inside of which the gradient of mixture composition is oriented normal to the direction of propagation. The simulations are performed using a two-component, single-step reaction model calibrated so that one-dimensional detonation properties of model low- and high-activation-energy mixtures are similar to those observed in a typical hydrocarbon–air mixture. In the low-activation-energy mixture, the reaction zone structure is complex, consisting of curved fuel-lean and fuel-rich detonations near the line of stoichiometry that transition to decoupled shocks and turbulent deflagrations near the channel walls where the mixture is extremely fuel-lean or fuel-rich. Reactants that are not consumed by the leading detonation combine downstream and burn in a diffusion flame. Detonation cells produced by the unstable reaction front vary in size across the channel, growing larger away from the line of stoichiometry. As the size of the channel decreases relative to the size of a detonation cell, the effect of the mixture composition gradient is lessened and cells of similar sizes form. In the high-activation-energy mixture, detonations propagate more slowly as the magnitude of the mixture composition gradient is increased and can be quenched in a large enough gradient.

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