REACTIONS OF ARYLSULPHONIC ESTERS: V. AN INTERPRETATION OF ACTIVATION ENERGIES OF SOLVOLYSIS OF METHYL BENZENESULPHONATE IN MIXED HYDROXYLIC SOLVENTS

1956 ◽  
Vol 34 (7) ◽  
pp. 931-941 ◽  
Author(s):  
J. B. Hyne ◽  
R. E. Robertson
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Aliphatic Alcohol ◽  
Activation Energies ◽  
Physical Significance ◽  
Activation Entropy ◽  
Experimental Uncertainty ◽  
Extended Form ◽  
Uncertainty Product ◽  
Alcohol Water

The rates of solvolysis of methyl benzenesulphonate at 50 ° and 75 °C. in several binary aliphatic alcohol–water mixtures have been determined over the composition ranges. The derived activation energies are compared with those calculated from an extended form of the equation employed in accounting for solvolytic activation energies in pure hydroxylic solvents. The physical significance of the equation is discussed in terms of a spectrum of solvolytic mechanisms covering the range between SN1 and SN2 mechanisms. The equation predicts activation energy values well within the experimental uncertainty. Product ratio and activation entropy data are shown to be in keeping with the reaction mechanism proposed.

scholarly journals Alkaline oxidative degradation of diphenylmethane structures — Activation energy and computational analysis of the reaction mechanism

2001 ◽  
Vol 79 (9) ◽  
pp. 1394-1401
Author(s):  
Lubo Jurasek ◽  
Lívia Krištofová ◽  
Yujun Sun ◽  
Dimitris S Argyropoulos
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Computational Analysis ◽  
Model Compound ◽  
Degradation Products ◽  
Oxidative Degradation ◽  
Semiempirical Method ◽  
Activation Energies ◽  
Ring Cleavage ◽  
Residual Lignin

A diphenylmethane model compound (2,2'-methylenebis[6-methoxy-4-methylphenol]) and residual kraft lignin were treated with alkaline hydrogen peroxide. Kinetic data for the disappearance of the model and the diphenylmethane structures in the residual lignin was collected. The activation energies for the degradation were found to be similar (54 ± 11 kJ mol–1 for the model and 58 ± 5 kJ mol–1 for the residual lignin). A comparison of the activation energies with the data of a previous study on a biphenyl model compound (3,3'-dimethoxy-5,5'-dimethyl-[1,1'-biphenyl]-2,2'-diol) showed a substantially higher activation energy for the degradation of the latter. Pathways for the degradation of 2,2'-methylenebis[6-methoxy-4-methylphenol] were proposed and the intermediates subjected to computational analysis using a semiempirical method (PM3). The results suggest that initially a common pathway exists, resulting in 2-[2-hydroxy-3-methoxy-5-methyl-phenylmethyl]-4-methyl-2,4-hexadienedioic acid. Then the pathway branches into three, resulting in three major degradation products. The main driving force of the reactions is the formation of radical sites after reaction with hydroxyl radicals and subsequent radical coupling with perhydroxyl radicals to form peroxides. All the reactions on the pathways are exothermic except for the transformations of peroxides into dioxetanes. The dioxetanes cleave exothermically resulting in ring cleavage and fragmentation. The computed data permitted for the rationalization as to why the diphenylmethane structures appear to be more labile than biphenyl structures under alkaline oxidative conditions.Key words: activation energy, alkaline oxidative degradation, computational chemistry, lignin, reaction mechanism.

Relationship between activation energy and pre-exponential factor normalized by the number of Brønsted acid sites in cracking of short chain alkanes on zeolites

2015 ◽  
Vol 5 (3) ◽  
pp. 1864-1869 ◽  
Author(s):  
Naonobu Katada ◽  
Satoko Sota ◽  
Nami Morishita ◽  
Kazu Okumura ◽  
Miki Niwa
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Acid Sites ◽  
Short Chain ◽  
Activation Entropy ◽  
Bronsted Acid ◽  
Brønsted Acid Sites ◽  
Exponential Factor ◽  
Brönsted Acid ◽  
Alkane Cracking

Two different relationships between activation entropy and enthalpy in alkane cracking over various zeolites suggest a difference in the reaction mechanism.

scholarly journals High-Temperature Deformation of Naturally Aged 7010 Aluminum Alloy

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 581
Author(s):  
Abdulhakim A. Almajid
Keyword(s):  
Activation Energy ◽  
Aluminum Alloy ◽  
High Temperature ◽  
Threshold Stress ◽  
Activation Energies ◽  
Temperature Deformation ◽  
High Temperature Range ◽  
Temperature Range ◽  
True Activation Energy ◽  
Two Temperatures

This study is focused on the deformation mechanism and behavior of naturally aged 7010 aluminum alloy at elevated temperatures. The specimens were naturally aged for 60 days to reach a saturated hardness state. High-temperature tensile tests for the naturally aged sample were conducted at different temperatures of 573, 623, 673, and 723 K at various strain rates ranging from 5 × 10−5 to 10−2 s−1. The dependency of stress on the strain rate showed a stress exponent, n, of ~6.5 for the low two temperatures and ~4.5 for the high two temperatures. The apparent activation energies of 290 and 165 kJ/mol are observed at the low, and high-temperature range, respectively. These values of activation energies are greater than those of solute/solvent self-diffusion. The stress exponents, n, and activation energy observed are rather high and this indicates the presence of threshold stress. This behavior occurred as a result of the dislocation interaction with the second phase particles that are existed in the alloy at the testing temperatures. The threshold stress decreases in an exponential manner as temperature increases. The true activation energy was computed by incorporating the threshold stress in the power-law relation between the stress and the strain. The magnitude of the true activation energy, Qt dropped to 234 and 102 kJ/mol at the low and high-temperature range, respectively. These values are close to that of diffusion of Zinc in Aluminum and diffusion of Magnesium in Aluminum, respectively. The Zener–Hollomon parameter for the alloy was developed as a function of effective stress. The data in each region (low and high-temperature region) coalescence in a segment line in each region.

The kinetics of hydration of tricalcium silicate

1970 ◽  
Vol 48 (21) ◽  
pp. 3291-3299 ◽  
Author(s):  
K. G. McCurdy ◽  
B. P. Erno
Keyword(s):  
Reaction Mechanism ◽  
Intermediate Product ◽  
Activation Energies ◽  
Tricalcium Silicate ◽  
Rate Data ◽  
Large Excess ◽  
First Order ◽  
Kinetics Of ◽  
Subsequent Decomposition

An investigation has been made of the kinetics of hydration of tricalcium silicate at several temperatures in a large excess of water in the presence of various added ions. The rate data have been interpreted by a reaction mechanism which involves: (a) the first order hydration of tricalcium silicate to form an intermediate product, 1.5CaO•SiO2, which can react by two pathways, (b) the direct first order decomposition of intermediate, 1.5CaO•SiO2, to form lime and silica or (b′) complexing of intermediate with silica and subsequent decomposition to form lime and silica. This reaction mechanism predicts the rate of production of base during the hydration. The effect of various added ions is interpreted in terms of the proposed mechanism.Rate constants and activation energies for the various steps in the proposed mechanism are reported.

scholarly journals Effect of CaO on catalytic combustion of semi-coke

2021 ◽  
Vol 10 (1) ◽  
pp. 011-020
Author(s):  
Luyao Kou ◽  
Junjing Tang ◽  
Tu Hu ◽  
Baocheng Zhou ◽  
Li Yang
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Combustion Rate ◽  
Activation Energies ◽  
Combustion Reaction ◽  
Tg Analysis ◽  
Conversion Rates ◽  
Apparent Activation Energies ◽  
Ozawa Integral Method ◽  
Addition Amount

Abstract Generally, adding a certain amount of an additive to pulverized coal can promote its combustion performance. In this paper, the effect of CaO on the combustion characteristics and kinetic behavior of semi-coke was studied by thermogravimetric (TG) analysis. The results show that adding proper amount of CaO can reduce the ignition temperature of semi-coke and increase the combustion rate of semi-coke; with the increase in CaO content, the combustion rate of semi-coke increases first and then decreases, and the results of TG analysis showed that optimal addition amount of CaO is 2 wt%. The apparent activation energy of CaO with different addition amounts of CaO was calculated by Coats–Redfern integration method. The apparent activation energy of semi-coke in the combustion reaction increases first and then decreases with the increase in CaO addition. The apparent activation energies of different samples at different conversion rates were calculated by Flynn–Wall–Ozawa integral method. It was found that the apparent activation energies of semi-coke during combustion reaction decreased with the increase in conversion.

scholarly journals The Effect of α-Al(MnCr)Si Dispersoids on Activation Energy and Workability of Al-Mg-Si-Cu Alloys during Hot Deformation

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Xiaoguo Wang ◽  
Jian Qin ◽  
Hiromi Nagaumi ◽  
Ruirui Wu ◽  
Qiushu Li
Keyword(s):  
Activation Energy ◽  
Aluminum Alloys ◽  
Constitutive Equation ◽  
Hot Deformation ◽  
Flow Instability ◽  
Void Formation ◽  
Activation Energies ◽  
Compression Tests ◽  
Softening Mechanism ◽  
Dynamic Softening

The hot deformation behaviors of homogenized direct-chill (DC) casting 6061 aluminum alloys and Mn/Cr-containing aluminum alloys denoted as WQ1 were studied systematically by uniaxial compression tests at various deformation temperatures and strain rates. Hot deformation behavior of WQ1 alloy was remarkably changed compared to that of 6061 alloy with the presence of α-Al(MnCr)Si dispersoids. The hyperbolic-sine constitutive equation was employed to determine the materials constants and activation energies of both studied alloys. The evolution of the activation energies of two alloys was investigated on a revised Sellars’ constitutive equation. The processing maps and activation energy maps of both alloys were also constructed to reveal deformation stable domains and optimize deformation parameters, respectively. Under the influence of α dispersoids, WQ1 alloy presented a higher activation energy, around 40 kJ/mol greater than 6061 alloy’s at the same deformation conditions. Dynamic recrystallization (DRX) is main dynamic softening mechanism in safe processing domain of 6061 alloy, while dynamic recovery (DRV) was main dynamic softening mechanism in WQ1 alloy due to pinning effect of α-Al(MnCr)Si dispersoids. α dispersoids can not only resist DRX but also increase power required for deformation of WQ1 alloy. The microstructure analysis revealed that the flow instability was attributed to the void formation and intermetallic cracking during hot deformation of both alloys.

New experiments on the relationship between light-induced defects and photoconductivity degradation

2001 ◽  
Vol 664 ◽  
Author(s):  
Stephan Heck ◽  
Howard M. Branz
Keyword(s):  
Activation Energy ◽  
Defect Density ◽  
Activation Energies ◽  
Dangling Bond ◽  
Fast Recovery ◽  
Slow Recovery ◽  
Degradation Model ◽  
Induced Defects ◽  
The Relationship ◽  
Hydrogenated Amorphous

ABSTRACTWe report experimental results that help settle apparent inconsistencies in earlier work on photoconductivity and light-induced defects in hydrogenated amorphous silicon (a-Si:H) and point toward a new understanding of this subject. After observing that light-induced photoconductivity degradation anneals out at much lower T than the light-induced increase in deep defect density, Han and Fritzsche[1] suggested that two kinds of defects are created during illumination of a-Si:H. In this view, one kind of defect degrades the photoconductivity and the other increases defect sub-bandgap optical absorption. However, the light-induced degradation model of Stutzmann et al.[2] assumes that photoconductivity is inversely proportional to the dangling-bond defect density. We observe two kinds of defects that are distinguished by their annealing activation energies, but because their densities remain in strict linear proportion during their creation, the two kinds of defects cannot be completely independent.In our measurements of photoconductivity and defect absorption (constant photocurrent method) during 25°C light soaking and during a series of isochronal anneals between 25 < T < 190°C, we find that the absorption measured with E ≤1.1 eV, first increases during annealing, then exhibits the usual absorption decrease found for deeper defects. The maximum in this absorption at E ≤1.1eV occurs simultaneously with a transition from fast to slow recovery of photoconductivity. The absorption for E ≤1.1eV shows two distinct annealing activation energies: the signal rises with about 0.87 eV and falls with about 1.15 eV. The 0.87 eV activation energy roughly equals the activation energy for the dominant, fast, recovery of photoconductivity. The 1.15 eV activation energy roughly equals the single activation energy for annealing of the light-induced dangling bond absorption.

Kinetics Studies for Catalytic Oxidation of Methyl Orange over the Heterogeneous Fe/Beta Catalysts

2013 ◽  
Vol 807-809 ◽  
pp. 361-364
Author(s):  
Fang Guo ◽  
Jun Qiang Xu ◽  
Jun Li
Keyword(s):  
Activation Energy ◽  
Hydrogen Peroxide ◽  
Reaction Mechanism ◽  
Methyl Orange ◽  
Incipient Wetness Impregnation ◽  
Kinetics Studies ◽  
Optimum Reaction ◽  
Catalyst Dosage ◽  
Oxidation Degradation ◽  
Degradation Of Methyl Orange

The Fe/Beta catalysts were prepared by conventional incipient wetness impregnation. The catalysis oxidation degradation of methyl orange was carried out in catalyst and H2O2 process. The results indicated that the catalyst and hydrogen peroxide were more benefit to degradation of methyl orange. The reaction condition was optimized. The optimum reaction process was as follow: iron amount of catalyst was 1.25%, the catalyst dosage and H2O2 concentration was 1 mg/L and 1.5 mg/L, and reaction temperature was 70 °C. The apparent activation energy (65 KJ/mol) was obtained according to the arrhenius formula, which was benefit to study the reaction mechanism.

scholarly journals On the catalytic dehydrogenation of naphthenes II. Competition experiments and energies of C-H bonds

1947 ◽  
Vol 190 (1022) ◽  
pp. 309-328 ◽  
Keyword(s):  
Activation Energy ◽  
Active Sites ◽  
Catalyst Surface ◽  
Resonance Energy ◽  
Activation Energies ◽  
Theoretical Treatment ◽  
Catalytic Dehydrogenation ◽  
Simple Relationship ◽  
Hydrogen Atoms ◽  
Methyl Cyclohexane

The rates of dehydrogenation in competition experiments using mixtures of two naphthenes, or a naphthene and a cyclic mono-olefine or two cyclic mono-olefines, have been examined theoretically and experimentally for the stationary state conditions. Provided the two reactants can occupy the same sites on the catalyst surface, then the ratio of the rates should be directly proportional to the ratio of the partial pressures at any instant. Theory suggests that a constant which can be derived from these competition experiments should be independent of the overall pressures, or of the initial ratio of concentrations or of the overall extent of dehydrogenation. Further, the ratio of the rates in competition should bear no simple relationship to the ratio of the individual rates alone, but should be related to the slopes of the 1/rate against 1/pressure plot for the two components considered separately. Moreover, the constant should be a ratio of two functions each of which is characteristic of one of the naphthenes. The theoretical conclusions have been confirmed experimentally which proves either that the groups of active sites on the catalyst surface are widely separated or that any set of sites is available for the reaction of any molecular species, and no interference takes place between naphthene molecules adsorbed on adjacent sites. Proof that a naphthene and cyclohexene are dehydrogenated on the same sites is supplied by the observation that a constant is obtained when different mixtures of cyclohexene and trans -1:4-dimethyl cyclohexane are allowed to compete for the surface. The ratios for methyl, ethyl, the three dimethyl and the three trimethyl cyclohexanes in competition with cyclohexane have been accurately determined at temperatures of 400 and 450° C. From the constants so derived the activation energy differences for the removal of the first pair of hydrogen atoms has been obtained. These values are discussed in terms of the possible transition complexes, and it is shown that the reaction proceeds by the loss of a pair of hydrogen atoms simultaneously and not by a half-hydrogenated state mechanism. Using these activation energies and the experimentally found overall activation energy of 36 kcal./g. mol., the resonance energy per resonating structure was determined as 1-73 kcal. This is in good agreement with the energies of C-H bonds in alkyl radicals (2-2 kcal./g.mol./ resonating structure). The theoretical treatment suggests that the weakest C-H link in methyl cyclohexane should be in the three position to the methyl group. A study of the activation energies involved shows that the methyl cyclohexene produced from methyl cyclohexane is not 1-methyl-1-cyclohexene, thus confirming the theoretical deduction.

scholarly journals Improvement in Carbonization Efficiency of Cellulosic Fibres Using Silylated Acetylene and Alkoxysilanes

Fibers ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 84
Author(s):  
Maria Mironova ◽  
Igor Makarov ◽  
Lyudmila Golova ◽  
Markel Vinogradov ◽  
Georgy Shandryuk ◽  
...  
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Thermal Behavior ◽  
Comparative Studies ◽  
Decomposition Reaction ◽  
Activation Energies ◽  
Composite Fibers ◽  
Carbon Yield ◽  
Pyrolysis Reaction ◽  
Cellulosic Fibres

Comparative studies of the structure and thermal behavior of cellulose and composite precursors with additives of silyl-substituted acetylene and alkoxysilanes were carried out. It is shown that the introduction of silicon-containing additives into the cellulose matrix influenced the thermal behavior of the composite fibers and the carbon yield after carbonization. Comparison of the activation energies of the thermal decomposition reaction renders it possible to determine the type of additive and its concentration, which reduces the energy necessary for pyrolysis. It is shown that the C/O ratio in the additive and the presence of the Si–C bond affected the activation energy and the temperature of the beginning and the end of the pyrolysis reaction.

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