Analysis of mechanism of the catalytic effect of hydrogen on the decay of alkyl macroradicals in polyethylene

1986 ◽  
Vol 51 (6) ◽  
pp. 1279-1286 ◽  
Author(s):  
Josef Bartoš
Keyword(s):  
Activation Energy ◽  
Kinetic Model ◽  
Energy Barrier ◽  
Catalytic Effect ◽  
Molecular Model ◽  
Particle State ◽  
One Step ◽  
The One ◽  
Step Mechanism ◽  
Phase Proceeds

The suggested one-step and two-step mechanism of decay of alkyl macroradicals in polyethylene are analyzed in detail at the activation energy level. For the one-step mechanism, the BEBO method is modified for reactions proceeding via a three-particle state. For the two-step mechanism, a three-process kinetic model is used; the contributions to the total energy barrier are calculated by the original BEBO method for two-particle transition states and by a molecular model for the diffusion of simple penetrants in polymers. The results indicate that the catalytic effect of hydrogen on the migration of the alkyls in the amorphous phase proceeds by the two-step mechanism.

scholarly journals MNDO and DFT Computational Study on the Mechanism of the Oxidation of 1,2-Diphenylhydrazine by Iodine

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Gideon A. Shallangwa ◽  
Adamu Uzairu ◽  
Victor O. Ajibola ◽  
Hamza Abba
Keyword(s):  
Reaction Mechanisms ◽  
Density Functional ◽  
Computational Study ◽  
The Other ◽  
Complex Mechanism ◽  
Functional Theory ◽  
One Step ◽  
The One ◽  
Activated Complex ◽  
Step Mechanism

The reaction mechanisms of the oxidation of 1,2-diphenylhydrazine by iodine have been examined using semiempirical and density functional theory methods, the oxidation proceeded via two independent pathways that can be separately monitored. One pathway involved the chain multistep mechanism. The other pathway occurred via a one-step mechanism in which a “cyclic” activated complex was formed which on disproportionation gave the products. The one-step “cyclic” activated complex mechanism proceeds more rapidly than the chain multistep mechanism. The results were explained by analyses based on computational energetics of the optimised reactants, intermediates, transition states, and products of the reaction of iodine with 1,2-diphenylhydrazine.

scholarly journals Kinetic Study of Thermal De-Chlorination of PVC-Containing Waste

2012 ◽  
Vol 730-732 ◽  
pp. 611-616 ◽  
Author(s):  
Alexandra Castro ◽  
Cândida Vilarinho ◽  
Delfim Soares ◽  
Fernando Castro
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Thermal Treatment ◽  
Kinetic Model ◽  
Energy Recovery ◽  
Order Reaction ◽  
Pyrolysis Process ◽  
First Order ◽  
Different Temperatures ◽  
The One

The presence of organic compounds on wastes, especially plastics, is considered an important source of energy. However, most of these plastics contain polyvinyl chloride (PVC), causing recycling problems when it is considered a thermal valorization process for its treatment [1], preventing the use of those residues on these processes, which main goal is the energy recovery [2,3]. A possible solution is to remove the chlorine from PVC containing waste through a pyrolysis process before being subjected to a thermal treatment, for energetic valorization. In this work, it was developed a kinetic model for the thermal decomposition of PVC, in view of its de-chlorination. DTA/TGA testing were performed at different temperatures (between the range of decomposition temperatures of the PVC molecule) indicated a first order reaction and an activation energy of 133800 J/mol, value very close to the one obtained in others works reported [4]. A factorial plan was carried out with different temperatures, performed in lab scale, in which best results were obtained at the temperature of 340 °C, proving the kinetic model obtained.

A Combined Topological ELF, NCI and QTAIM Study of Mechanism and Hydrogen Bond Controlling the Selectivity of the IMDC Reaction of Nitrone-alkene Obtained from m-allyloxybenzaldehyde

2020 ◽  
Vol 17 (4) ◽  
pp. 260-267 ◽  
Author(s):  
Fouad Chafaa ◽  
Abdelmalek Khorief Nacereddine ◽  
Abdelhafid Djerourou
Keyword(s):  
Activation Energy ◽  
Hydrogen Bond ◽  
Transition State ◽  
Molecular Mechanism ◽  
Theoretical Method ◽  
Noncovalent Interaction ◽  
Covalent Interaction ◽  
Energy Profiles ◽  
One Step ◽  
Step Mechanism

The selectivity and molecular mechanism of the intramolecular [3+2] cycloaddition (IMDC) reaction of nitrone-alkene generated from m-allyloxybenzaldehyde has been studied computationally using B3LYP/6-31G(d) theoretical method. The energy profiles indicate that this IMDC reaction favours kinetically the formation of the fused-endo, as observed experimentally. The solvent has no influence on the mechanism and selectivity, but it increases slightly the activation energy and decreases the exothermic character of this IMDC reaction. The analysis through electron localisation function (ELF) of the favourable fused-endo pathway shows that the formation of the C–O and C–C new bonds occurred via a non-concerted synchronous one-step mechanism. The analysis of noncovalent interaction using Non-covalent interaction (NCI) and QTAIM analyses of the structure of the fused-endo transition state indicates that the hydrogen-bond formed at this approach is the origin for the favouring of the fused-endo pathway.

Study on Pyrolysis Characteristics of Corn Straw

2011 ◽  
Vol 9 (1) ◽  
Author(s):  
Zhengqi Li ◽  
Zhichao Chen ◽  
Chunlong Liu ◽  
Zhiyong Hu ◽  
Wei Zhao ◽  
...  
Keyword(s):  
Activation Energy ◽  
Mass Loss ◽  
Loss Ratio ◽  
Corn Straw ◽  
Heating Rates ◽  
Pyrolysis Characteristics ◽  
Ratio Curve ◽  
Step Model ◽  
One Step ◽  
The One

Pyrolysis characteristics of corn straw samples (corn stalks skins, corn stalks cores, corn bracts and corn leaves) was performed using thermogravimetric analysis Three heating rates (20, 50 and 100 k min-1) were applied with a final temperature of 900°C. The maximum pyrolysis rates increased with the heating rate increasing and the temperature at the peak pyrolysis rate also increased. The activation energy and the temperature interval of pyrolysis for these samples had only slightly increasing at different heating rates. The one-step model was used to obtain the pre-exponential and the activation energy. Through calculating, we obtain the mass loss ratio curve. The three models have similar results. The one-step model is simpler and suitable for the simulation of the mass loss ratio curve.

scholarly journals Atmospheric band fitting coefficients derived from a self-consistent rocket-borne experiment

2019 ◽  
Vol 19 (2) ◽  
pp. 1207-1220 ◽  
Author(s):  
Mykhaylo Grygalashvyly ◽  
Martin Eberhart ◽  
Jonas Hedin ◽  
Boris Strelnikov ◽  
Franz-Josef Lübken ◽  
...  
Keyword(s):  
Atomic Oxygen ◽  
Band Emission ◽  
Self Consistent ◽  
Volume Emission ◽  
Volume Measurements ◽  
One Step ◽  
The One ◽  
Background Air ◽  
Atomic Oxygen Concentration ◽  
Step Mechanism

Abstract. Based on self-consistent rocket-borne measurements of temperature, the densities of atomic oxygen and neutral air, and the volume emission of the atmospheric band (762 nm), we examined the one-step and two-step excitation mechanism of O2b1Σg+ for nighttime conditions. Following McDade et al. (1986), we derived the empirical fitting coefficients, which parameterize the atmospheric band emission O2b1Σg+-X3Σg-0,0. This allows us to derive the atomic oxygen concentration from nighttime observations of atmospheric band emission O2b1Σg+-X3Σg-0,0. The derived empirical parameters can also be utilized for atmospheric band modeling. Additionally, we derived the fit function and corresponding coefficients for the combined (one- and two-step) mechanism. The simultaneous common volume measurements of all the parameters involved in the theoretical calculation of the observed O2b1Σg+-X3Σg-0,0 emission, i.e., temperature and density of the background air, atomic oxygen density, and volume emission rate, is the novelty and the advantage of this work.

Thermooxidative degradation and its kinetics of natural rubber coagulated by microwave radiation

2012 ◽  
Vol 32 (8-9) ◽  
pp. 511-517 ◽  
Author(s):  
Lu-Sheng Liao ◽  
Jian-He Liao ◽  
Yi-Min Li ◽  
Yong-Ping Chen ◽  
Yan-Fang Zhao ◽  
...  
Keyword(s):  
Activation Energy ◽  
Kinetic Model ◽  
Natural Rubber ◽  
Microwave Radiation ◽  
Preexponential Factor ◽  
Degradation Process ◽  
Main Stage ◽  
Thermooxidative Degradation ◽  
Mean Values ◽  
One Step

Abstract The thermooxidative degradation of natural rubber (NR) coagulated by microwave radiation (NR-m) was investigated by thermogravimetry (TG) analysis, and compared with NR coagulated by acid (NR-a). It was found that the degradation process is not a one-step reaction, the main degradation process occurs at 300–400ºC, and the equilibrium degradation temperatures of NR-m are higher than those of NR-a. Different methods were used to find the most probable kinetic model and the Arrhenius para­meters (activation energy E and preexponential factor A) for the main stage of thermooxidative degradation of NR-m. The results show that the values of E and A, obtained from the Coats-Redfern method, are highly variable with the kinetic model chosen and the heating rate (β), and the apparent activation energy (E0) when β approaches zero for the Dn type kinetic model is in the range of 96.7–106.4 kJ ∙ mol-1. The mean values of E, calculated by the Friedman and Flynn-Wall-Ozawa (FWO) methods, are 113.8 and 83.3 kJ ∙ mol-1, respectively, suggesting E in the range of 83.3–113.8 kJ ∙ mol-1. Comparison of these two ranges indicates the most probable kinetic model to be Dn type kinetic models, corresponding to a diffusion-controlled mechanism.

scholarly journals Approaches to Biomass Kinetic Modelling: Thermochemical Biomass Conversion Processes

2021 ◽  
Vol 4 (Vol4) ◽  
pp. 1-13
Author(s):  
Omar Al-Ayed
Keyword(s):  
Activation Energy ◽  
Kinetic Models ◽  
Design Procedure ◽  
Network Models ◽  
Frequency Factor ◽  
Biomass Pyrolysis ◽  
Kinetic Triplet ◽  
One Step ◽  
The One

Modeling of biomass pyrolysis kinetics is an essential step towards reactors design for energy production. Determination of the activation energy, frequency factor, and order of the reaction is necessary for the design procedure. Coats and Redfern's work using the TGA data to estimate these parameters was the cornerstone for modeling. There are two significant problems with biomass modeling, the first is the determination of the kinetic triplet (Activation energy, Frequency factor, and the order of reaction), and the second is the quantitative analysis of products distribution. Methods used in modeling are either One-step or Multistep methods. The one-step techniques allow the determination of kinetic triplet but fail to predict the product distribution, whereas multistep processes indicate the product's distribution but challenging to estimate the parameters. Kissinger, Coats, and Redfern, KAS, FWO, Friedman are one-step methods that have been used to estimate the kinetic parameters. In this work, after testing more than 500 data points accessed from different literature sources for coal, oil shale, solid materials, and biomass pyrolysis using one-step global method, it was found that the activation energy generated by KAS or FWO methods are related as in the following equations: 𝐸𝐾𝐴𝑆 = 0.9629 ∗ 𝐸𝐹𝑊𝑂 + 8.85, with R² =0.9945 or 𝐸𝐹𝑊𝑂 = 1.0328 ∗ 𝐸𝐾𝐴𝑆 − 8.0969 with R2= 0.9945. The multistep kinetic models employed the Distributed Activation Energy Model (DAEM) using Gaussian distribution, which suffers from symmetry, other distributions such as Weibull, and logistic has been used. These multistep kinetic models account for parallel/series and complex, primary and secondary biomass reactions by force-fitting the activation energy values. The frequency factor is assumed constant for the whole range of activation energy. Network models have been used to account for heat and mass transfer (diffusional effects), where the one-step and multistep could not account for these limitations. Three network models are available, the Bio-CPD (Chemical Percolation Devolatilization) model, Bio-FLASHCHAIN, and the Bio-FGDVC (Functional Group Depolymerization Vaporization Crosslinking models). These models tried to predict the product distributions of the biomass pyrolysis process

scholarly journals Rigorous equations for isothermal titration calorimetry: theoretical and practical consequences

2019 ◽  
Author(s):  
Philippe Dumas
Keyword(s):  
Isothermal Titration Calorimetry ◽  
Titration Calorimetry ◽  
Single Pair ◽  
Mathematical Methods ◽  
Injection Method ◽  
Titration Curves ◽  
Preliminary Version ◽  
One Step ◽  
The One ◽  
Step Mechanism

AbstractA preliminary version of this work, [doi.org/10.1101/512780], was deposited in bioRχiv on January 6, 2019, and in a revised form on May 15, 2019New mathematical methods have been developed for processing titration curves (TC) obtained from Isothermal Titration Calorimetry (ITC). Exact TC equations for the usual multi-injection method (MIM), or for the single-injection method (SIM) with continuous injection, were derived by taking into account rigorously the effect of dilution resulting from the titration process. Several practical consequences of these results are discussed. An exact fit of a TC can thus be obtained, even with large injected volumes leading to important dilution. All available programs show systematic differences with the exact results, NanoAnalyze from TA being significantly more accurate. A part of the results have been incorporated into AFFINImeter from S4SD. It is also examined how certain multi-step mechanisms are in fact thermodynamically equivalent to the one-step association/dissociation mechanism. They will thus never explain any “atypical” TC not showing the classical sigmoid shape. Although only a single pair of parameters (Kd and ΔH) can explain an experimental TC compatible with the one-step mechanism, an infinite number of parameters explain equally well the same data with such an equivalent multi-step mechanism. An explicit link between the two sets of parameters is given. A parallel with the concept of gauge invariance in physics is proposed.Statement of significanceThis work reconsiders in full the processing of ITC data by taking into account exactly the dilution due to the titration. New equations are obtained both for the single and multiple injection methods, which suppresses systematic problems in commonly used programs. The method is made practically available to everyone.

A Study on the Rearrangement of Dialkyl 1-Aryl-1-hydroxymethylphosphonates to Benzyl Phosphates

2020 ◽  
Vol 24 (4) ◽  
pp. 465-471 ◽  
Author(s):  
Zita Rádai ◽  
Réka Szabó ◽  
Áron Szigetvári ◽  
Nóra Zsuzsa Kiss ◽  
Zoltán Mucsi ◽  
...  
Keyword(s):  
Quantum Chemical ◽  
Room Temperature ◽  
Phase Transfer ◽  
One Pot ◽  
Substrate Dependence ◽  
Triethylbenzylammonium Chloride ◽  
One Step ◽  
The Pudovik Reaction ◽  
The One ◽  
Solid Liquid

The phospha-Brook rearrangement of dialkyl 1-aryl-1-hydroxymethylphosphonates (HPs) to the corresponding benzyl phosphates (BPs) has been elaborated under solid-liquid phase transfer catalytic conditions. The best procedure involved the use of triethylbenzylammonium chloride as the catalyst and Cs2CO3 as the base in acetonitrile as the solvent at room temperature. The substrate dependence of the rearrangement has been studied, and the mechanism of the transformation under discussion was explored by quantum chemical calculations. The key intermediate is an oxaphosphirane. The one-pot version starting with the Pudovik reaction has also been developed. The conditions of this tandem transformation were the same, as those for the one-step HP→BP conversion.

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