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1.
A critical analysis is presented of the use of an overall single rate reaction equation instead of the true rate equation
corresponding to a complex process consisting of two consecutive reactions. In accordance with this approximation, which is
often used in the kinetic analysis of systems in which several reactions take place, the overall process is described by apparent
activation parameters (the apparent activation energy Eap and the apparent pre-exponential factor Aap) and an apparent conversion function.
The theoretical isotherms (α=α(t), where α is the conversion degree and t is time) were simulated for a system in which two
consecutive reactions occur. In this case, the apparent activation parameters depend on (a) the considered range of temperature;
and (b) the temperature for a given conversion degree. It is shown that the apparent activation parameters are correlated
by the compensation effect relationship: ln Aap = α* + β*Eap where α* and β* are the linear regression parameters.
The possibility of using the apparent kinetic parameters to predict the isotherms α=α(t) for temperatures lower than those
for which these parameters were evaluated is discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
The theoretical isotherms (α=α(t), where α is the conversion degree and t is the time) and the theoretical thermogravimetric curves(α=α(T), where T is the temperature) were simulated for a system in which two consecutive reactions occur. A critical analysis of the use
of an overall single rate reaction equation instead of the use of the true rate equations is presented. Both for isothermal
and non-isothermal data and α≤0.50, the apparent reaction order depends on temperature. It is pointed out that the apparent
reaction order for a given temperature can be evaluated if the parameters of the compensation effect are known.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Ammonium dinitramide (ADN) prills were prepared by emulsion crystallization and characterized by optical microscopic, thermogravimetric
(TG) and differential scanning calorimetric (DSC) techniques. The isothermal and non-isothermal decomposition kinetics of
ADN prills were studied by TG. The differential isoconversional method of Friedman (FR) and integral isoconversional method
of Vyazovkin were used to investigate the dependence of activation energy (E
a) with conversion (α) and the results were compared with literature data. The dependence of activation energy was also derived
from isothermal data. A strong dependence of E
a with α is observed for the ADN prills. All the methods showed an initial increase in E
a up to α=∼0.2 and later decreases over the rest of conversion. The apparent E
a values of FR method are higher than that of Vyazovkin method up to α=∼0.45. The calculated mean E
a values by FR, Vyazovkin and standard isoconversional method for α between 0.05 and 0.95 were 211.0, 203.9 and 156.9 kJ mol−1, respectively. 相似文献
4.
We have determined the parameters of the Arrhenius equation (E, log A) for reactions between
\textNO2+ {\text{NO}}_2^{+} ions and C3-C8 alkanes in HNO3–93 wt.% H2SO4 solutions at 277–353 K, and we have also estimated the activation parameters E
j
, log A
j
for secondary and tertiary C—H bonds of these alkanes. We show that the following compensation relations are satisfied: E = 2.3R βlog A + C with isokinetic temperature β = 360 ± 65 K, and also E
j
=2.3Rβ
j
log A
j
+ C
j
, for secondary C—H bonds, β2 =300 ± 60, and for tertiary C—H bonds, β3 =310 ± 50. 相似文献
5.
In this paper, evaluation of kinetic parameters (the activation energy – E,the pre-exponential factor – A and the reaction order – n) with simultaneous determination of the possible reaction mechanism of thermal decomposition of calcium hydroxide (portlandite),
Ca(OH)2 formed during hydration of commercial Portland-slag cement, by means of differential scanning calorimetry (DSC) in non-isothermal
conditions with a single heating–rate plot has been studied and discussed. The kinetic parameters and a mechanism function
were calculated by fitting the experimental data to the integral, differential and rate equation methods.
To determine the most probable mechanism, 30 forms of the solid-state mechanism functions, f(αc) have been tried. Having used the procedure developed and the appropriate program support, it has been established that the
non-isothermal thermal decomposition of calcium hydroxide in the acceleratory period (0.004<αc<0.554) can be described by the rate equation: d αc/dT=A/βexp(−E/RT)f(αc), which is based on the concept of the mechanism reaction:f(αc)=2(αc)1/2.
The mechanism functions as well as the values of the kinetic parameters are in good agreement with those given in literature.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Le Xin Song Chuan Feng Teng Peng Xu Hai Ming Wang Zi Qiang Zhang Qing Qing Liu 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):223-233
The present work revealed there was a conceptual difference in the thermal decomposition behaviors between the complexed β-cyclodextrin
(CD) in an inclusion system and the β-CD complex of guest. The thermal decomposition behaviors of the solid inclusion complexes
of β-CD with ethylenediamine (Eda), diethylenetriamine (Dta) and triethylamine (Tea) were investigated using nonisothermal
thermogravimetry (TG) analysis based on weight loss as a function of temperature. In view of TG profiles, a consecutive mechanism
describing the formation and thermal decomposition of the three solid supermolecules of β-CD was presented. Heating rate has
very different effects on the thermal decomposition behaviors of these complexes. The faster the heating rate is, the higher
the melting-decomposition point of the complexed β-CD in an inclusion system is, and on the whole the bigger the rate constant
(k) of the thermal decomposition reaction of the complexed β-CD is. The thermal decomposition process of the complexed β-CD
for each inclusion system is determined to be simple first-order reaction using Ozawa method. The apparent activation energies
(E
a) and frequency factors (A) of the thermal decomposition reactions of the complexed β-CD molecules have been also calculated. It is found that when
the decomposition reaction of the complexed β-CD encountered a large value of E
a, such as that in Dta–β-CD system, an apparent compensation effect of A on E
a can provide enough energy to conquer the reaction barrier in prompting the k value of thermal decomposition reaction of the complexed β-CD according to Arrhenius equation. 相似文献
7.
S. -X. Wang Z. -C. Tan Y. -S. Li L. -X. Sun Y. Li 《Journal of Thermal Analysis and Calorimetry》2008,92(2):483-487
Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO2 composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these
two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and
Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression
method. The results show that the kinetic models for the decomposition process of PANI/ZrO2 composite and PANI are all D3, and the corresponding function is ƒ(α)=1.5(1−α)2/3[1−(1-α)1/3]−1. The correlated kinetic parameters are E
a=112.7±9.2 kJ mol−1, lnA=13.9 and E
a=81.8±5.6 kJ mol−1, lnA=8.8 for PANI/ZrO2 composite and PANI, respectively. 相似文献
8.
H. M. Ye N. Ren H. Li J. J. Zhang S. J. Sun L. Tian 《Journal of Thermal Analysis and Calorimetry》2010,101(1):205-211
The complex of [Nd(BA)3bipy]2 (BA = benzoic acid; bipy = 2,2′-bipyridine) has been synthesized and characterized by elemental analysis, IR spectra, single
crystal X-ray diffraction, and TG/DTG techniques. The crystal is monoclinic with space group P2(1)/n. The two–eight coordinated Nd3+ ions are linked together by four bridged BA ligands and each Nd3+ ion is further bonded to one chelated bidentate BA ligand and one 2,2′-bipyridine molecule. The thermal decomposition process
of the title complex was discussed by TG/DTG and IR techniques. The non-isothermal kinetics was investigated by using double
equal-double step method. The kinetic equation for the first stage can be expressed as dα/dt = A exp(−E/RT)(1 − α). The thermodynamic parameters (ΔH
≠, ΔG
≠, and ΔS
≠) and kinetic parameters (activation energy E and pre-exponential factor A) were also calculated. 相似文献
9.
Synthesis and thermal decomposition kinetics of Th(IV) complex with unsymmetrical Schiff base ligand
Fan Yuhua Bi Caifeng Liu Siquan Yang Lirong Liu Feng Ai Xiaokang 《Journal of Radioanalytical and Nuclear Chemistry》2005,266(1):89-93
Summary A new unsymmetrical Schiff base ligand (H2LLi) was synthesized using L-lysine, o-vanillin and salicylaladyde. Thorium(IV) complex of this ligand [Th(H2L)(NO3)](NO3)2.3H2O have been prepared and characterized by elemental analyses, IR, UV and molar conductance. The thermal decomposition kinetics
of the complex for the second stage was studied under non-isothermal condition by TG and DTG methods. The kinetic equation
may be expressed as: dα/dt=A.e-E/RT.1/2 (1-α).[-ln(1-α)]-1. The kinetic parameters (E, A), activation entropy ΔS1and activation free-energy ΔG1were also calculated. 相似文献
10.
Shashi B. Kalia Priyanka Sankhyan R. Puri J. Christopher 《Journal of Thermal Analysis and Calorimetry》2012,107(2):597-605
Non-isothermal techniques, i.e. thermogravimetry (TG) and differential scanning calorimetry (DSC), have been applied to investigate
the thermal behaviour of carbaryl (1-naphthyl-N-methylcarbamate = 1-Naph-N-Mecbm) and its complexes, M(1-Naph-N-Mecbm)4X2, where M = Cu, X = Cl, NO3 and CH3COO and M = Zn, X = Cl. Carbaryl and Zn(1-Naph-N-Mecbm)4Cl2 complex exhibit two-stage thermal decomposition while the copper(II) complexes exhibit three and four-stage decomposition
in their TG curves. The nature of the metal ion has been found to play highly influential role on the nature of thermal decomposition
products as well as energy of activation ‘E*’. The presence of different anions does not seem to alter the thermal decomposition patterns. The complexes display weak
to medium intensity exothermic and endothermic DSC curves, while the free ligand exhibits two endothermic peaks. The kinetic
and thermodynamic parameters namely, the energy of activation ‘E*’, the frequency factor ‘A’ and the entropy of activation ‘S*’ etc. have been rationalized in relation to the bonding aspect of the carbaryl ligand. The nature and chemical composition
of the residues of the decomposition steps have been studied by elemental analysis and FTIR data. 相似文献
11.
Derivative of 8-hydroxyquinoline i.e. Clioquinol is well known for its antibiotic properties, drug design and coordinating
ability towards metal ion such as Copper(II). The structure of mixed ligand complexes has been investigated using spectral,
elemental and thermal analysis. In vitro anti microbial activity against four bacterial species were performed i.e. Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens, Bacillus substilis and found that synthesized complexes (15–37 mm) were found to be significant potent compared to standard drugs (clioquinol
i.e. 10–26 mm), parental ligands and metal salts employed for complexation. The kinetic parameters such as order of reaction
(n = 0.96–1.49), and the energy of activation (E
a = 3.065–142.9 kJ mol−1), have been calculated using Freeman–Carroll method. The range found for the pre-exponential factor (A), the activation entropy (S* = −91.03 to−102.6 JK−1 mol−1), the activation enthalpy (H* = 0.380–135.15 kJ mol−1), and the free energy (G* = 33.52–222.4 kJ mol−1) of activation reveals that the complexes are more stable. Order of stability of complexes were found to be [Cu(A4)(CQ)OH] · 4H2O > [Cu(A3)(CQ)OH] · 5H2O > [Cu(A1)(CQ)OH] · H2O > [Cu(A2)(CQ)OH] · 3H2O 相似文献
12.
Mohammad Khodadadi-Moghaddam Aziz Habibi-Yangjeh Mohamad Reza Gholami 《Monatshefte für Chemie / Chemical Monthly》2009,39(10):329-334
Abstract
Solvatochromic parameters (E T N, normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) have been determined for binary mixtures of propan-2-ol, propan-1-ol, ethanol, methanol and water with recently synthesized ionic liquid (IL; 2-hydroxyethylammonium formate) at 25 °C. In all solutions except aqueous solution, E T N values of the media increase abruptly with the ILs mole fraction and then increase gradually to the value of pure IL. A synergistic behavior is observed for the α parameter in all solutions. The behavior of π* and β are nearly ideal for all solutions except for solutions of methanol with the IL. The applicability of nearly ideal combined binary solvent/Redlich–Kister equation was proved for the correlation of various solvatochromic parameters with solvent composition. The correlation between the calculated and the experimental values of various parameters was in accordance with this model. Solute–solvent and solvent–solvent interactions were applied to interpret the results. 相似文献13.
Synthesis and thermal decomposition kinetics of La(III) complexwith unsymmetrical Schiff base ligand
Y. H. Fan Z. X. Gao C. F. Bi S. T. Xie X. Zhang 《Journal of Thermal Analysis and Calorimetry》2008,91(3):919-923
A new unsymmetrical solid Schiff base (LLi) was synthesized using L-lysine, o-vanillin and 2-hydroxy-l-naphthaldehyde. Solid lanthanum(III) complex of this ligand [LaL(NO3)]NO3·2H2O have been prepared and characterized by elemental analyses, IR, UV and molar conductance. The thermal decomposition kinetics
of the complex for the second stage was studied under non-isothermal condition by TG and DTG methods. The kinetic equation
may be expressed as: dα/dt=Ae−E/RT(1−α)2. The kinetic parameters (E, A), activation entropy ΔS
# and activation free-energy ΔG
# were also gained. 相似文献
14.
E. S. Rajagopal 《Colloid and polymer science》1961,175(2):126-129
Summary A working model is given for the rate of ultrasonic emulsification, considering the dispersion at the interface (areaA) and the coagulations in the volumeV of the emulsion. A bimolecular coagulation leads to the equationc=c
∞tanhbt;c
∞=(Aα/Vβ)1/2;b=(Aαβ/V)1/2 while a monomolecular coagulation givesc=c
∞{1−exp (−at)};c
∞=Aα/Vβ;a=β.
The experiments on the dependence of c∞,a andb uponA andV favour the bimolecular coagulation. The results are satisfactorily explained on general theoretical grounds.
Zusammenfassung Ein Arbeitsmodell für die Geschwindigkeit der Ultraschallemulgierung wird entwickelt, das Dispersion in der Grenzfl?che (Fl?cheA) und Koagulation im Volumen (V) der Emulsion annimmt. Eine bimolekulare Koagulation führt zu der Gleichung:c=c ∞ tanhbt;c ∞=(Aα/Vβ)1/2;b=(Aαβ/V)1/2, eine monomolekulare dagegen zu:c=c ∞{1−exp (at−)};c ∞=Aα/Vβ;α=β. Die Versuche über die Abh?ngigkeit vonc ∞,a undb vonA undV scheinen für bimolekulare Koagulation zu sprechen. Die Ergebnisse werden auf der Basis dieser einfachen theoretischen Grundlagen befriedigend erkl?rt.相似文献
15.
Zhang J.-J. Wang R.-F. Li J.-B. Liu H.-M. Yang H.-F. 《Journal of Thermal Analysis and Calorimetry》2000,62(3):747-755
The thermal decomposition of Eu2(BA)6(bipy)2 (BA=C2H5N–
2, benzoate; bipy=C10H8N2, 2,2'-bipyridine)and its kinetics were studied under the non-isothermal condition by TG-DTG, IR and SEM methods. The kinetic
parameters were obtained from analysis of the TG-DTG curves by the Achar method, the Madhusudanan-Krishnan-Ninan (MKN) method,
the Ozawa method and the Kissinger method. The most probable mechanism function was suggested by comparing the kinetic parameters.
The kinetic equation for the first stage can be expressed as: dα/dt=Aexp(–E/RT)3(1–α)2/3.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
Mohammad Khodadadi-Moghaddam Aziz Habibi-Yangjeh Mohamad Reza Gholami 《Monatshefte für Chemie / Chemical Monthly》2009,140(3):329-334
Abstract Solvatochromic parameters (E
T
N, normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) have been determined for binary mixtures of propan-2-ol, propan-1-ol, ethanol, methanol and
water with recently synthesized ionic liquid (IL; 2-hydroxyethylammonium formate) at 25 °C. In all solutions except aqueous
solution, E
T
N values of the media increase abruptly with the ILs mole fraction and then increase gradually to the value of pure IL. A synergistic
behavior is observed for the α parameter in all solutions. The behavior of π* and β are nearly ideal for all solutions except for solutions of methanol with the IL. The applicability of nearly ideal combined
binary solvent/Redlich–Kister equation was proved for the correlation of various solvatochromic parameters with solvent composition.
The correlation between the calculated and the experimental values of various parameters was in accordance with this model.
Solute–solvent and solvent–solvent interactions were applied to interpret the results.
Graphical Abstract Predicted values of solvatochromic parameters (SP) (E
T
N, normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) from the correlation equations versus its experimental values for binary mixtures of 2-hydroxyethylammonium
formate with water, methanol, ethanol, propan-1-ol and propan-2-ol.
相似文献
17.
A. F. Santos L. Polese M. S. Crespi C. A. Ribeiro 《Journal of Thermal Analysis and Calorimetry》2009,96(1):287-291
The non-isothermal data given by TG curves for poly(3-hydroxybutyrate) (PHB) were studied in order to obtain a consistent
kinetic model that better represents the PHB thermal decomposition. Thus, data obtained from the dynamic TG curves were suitably
managed in order to obtain the Arrhenius kinetic parameter E according to the isoconversional F-W-O method. Once the E parameters is found, a suitable logA and kinetic model (f(α)) could be calculated. Hence, the kinetic triplet (E±SD, logA±SD and f(α)) obtained for the thermal decomposition of PHB under non-isothermal conditions was E=152±4 kJ mol−1, logA=14.1±0.2 s−1 for the kinetic model, and the autocatalytic model function was: f(α)=αm(1−α)n=α0.42(1−α)0.56. 相似文献
18.
Two new polyhydroxysteroids and five new glycosides were isolated from the starfishCeramaster patagonicus and their structures were elucidated: 5α-cholestane-3β,6α,15β,16β,26-pentol, (22E)-5α-cholest-22-ene-3β,6α,8,15α,24-pentol, (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β,4β, 6α,8,15β,16β,28-heptol (ceramasteroside C1), (22E)-28-O-[O-(2,4-di-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β, 6α,8,15β,16β,28-hexol (ceramasteroside C2), (22E)-28-O-[O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β,6α,8,15β,16β 28-hexol (eramasteroside C3), (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-methyl-5α-cholest-22-ene-3β,4β,6α,8, 15β, 26-hexol (ceramasteroside C4), and (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-xylopyranosyl]-5α-cholest-22-ene-3β,6α,8,15β,24-pentol (ceramasteroside C5)). Three known polyhydroxysteroids (24-methylene-5α-cholestane-3β,6α,8,15β,16β,26-hexol, 5α-cholestane-3β,6α,8,15β,16β,26-hexol,
and 5α-cholestane-3β,6β,15α,16β,26-pentol) were also isolated.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 190–195, January, 1997. 相似文献
19.
20.
Catalytic activity of catalase (CAT) immobilized on a modified silicate matrix to mediate decomposition of meta-chloroperoxibenzoic
acid (3-CPBA) in acetonitrile has been investigated by means of quantitative UV-spectrophotometry. Under the selected experimental
conditions, the kinetic parameters: the apparent Michaelis constat (K
M
), the apparent maximum rate of enzymatic reaction (V
max
app
), the first order specific rate constants (k
sp
), the energy of activation (E
a
) and the pre-exponential factor of the Arrhenius equation (Z0) were calculated. Conclusions regarding the rate-limiting step of the overall catalytic process were drawn from the calculated
values of the Gibbs energy of activation ΔG*, the enthalpy of activation ΔH*, and the entropy of activation ΔS*. 相似文献