Meaningful activation energies for complex systems

Dowdy, D. R.

doi:10.1007/bf01914556

Cited by 41 publications

(16 citation statements)

References 17 publications

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“…Based on the theoretical consideration [13][14][15][16] about the influence of different models of kinetics schemes on the changes of the kinetics parameters with degrees of conversion, the conventional MMA polymerization could be explained with the existence of the kinetics scheme with two parallel reactions in which the first one is reversible while the second one is irreversible. For small values of degrees of conversion (a 30%) MMA polymerization under the conventional conditions, occurs the reversible stage (initiation) which is due to that characterized with high values of activation energy.…”

Section: Resultsmentioning

confidence: 99%

Comparison of the kinetics of conventional and microwave methyl methacrylate polymerization

Jovanović

Adnadjević

2007

J of Applied Polymer Sci

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A comparative investigation of the conventional and microwaves kinetics of methyl methacrylate (MMA) polymerization was performed. A method for determining the increase of the reaction rate in the microwave field (b) was presented. It was found that at all of the investigated temperatures and powers the polymerization rates increased in the presence of microwave energy by up to 8.9 times compared with conventional polymerization. Isothermal kinetics of the conventional MMA polymerization was investigated and its parameters were determined using isoconversion method. It was found that the calculated kinetics parameters changes complexly with degree of MMA conversion (a) and are in the mutual linear functional relationship, which is so called ''compensation effect.'' The complex changes of the kinetics parameters with a are explained with the postulated model for the mechanism of the MMA polymerization. The kinetics of the MMA polymerization under the microwave field (MWF) with different input power was investigated and its parameters were determined on the basis of the conversion-temperature curves and Arrhenius equation. The values of the kinetics parameters for MMA polymerization in the MWF are dependent on a and are from 1.2 to 12 times lower than that for conventional MMA polymerization. A new method for the determination of activation energy (E a ) of the investigated process in the MWF was described. Decreased E a value of the polymerization process in the MWF compared with the conventional polymerization is explained with the formation of the nonequilibrium energetic distribution of the reactants due to the rapid transfer of energy in the reaction system.

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Section: Resultsmentioning

confidence: 99%

Comparison of the kinetics of conventional and microwave methyl methacrylate polymerization

Jovanović

Adnadjević

2007

J of Applied Polymer Sci

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“…It must be pointed out that a number of computer programs for deconvolution have been proposed in the literature in the past few years [50][51][52], but their application is restricted to "n-order" reactions. Therefore, for the kinetic analysis of s-s reactions where this type of mechanism has no physical meaning, it would be interesting to develop a general method for deconvoluting complex reactions with overlapping processes without restriction with regard to the physico-geometric model satisfied by the elementary reactions.…”

Section: Competitive Reactionsmentioning

confidence: 99%

The kinetics of solid‐state reactions toward consensus, Part 2: Fitting kinetics data in dynamic conventional thermal analysis

Ortega¹

2002

Int J of Chemical Kinetics

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This paper is the second part of a review of some of the controversial kinetic aspects of conventional thermal analysis (TA). In this part the physico-geometric kinetics for the solid-state reactions were examined. The main problems discussed are (1) problems in fitting kinetics data: the identification of the f (α) function, (2) the suitability of conventional dynamic methods of TA, and (3) the complex reactions.

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“…The integration of Eq. (8) for unit reactions fitting a first-order model (F 1, A2 and A3 in Table 1) gives (10) (nai # 1)…”

Section: Theoreticalmentioning

confidence: 99%

“…In such a case, the problem can only be resolved mathematically. It must be pointed out that a number of computer programs for deconvoiution have been proposed in the literature [9][10], but their application is restricted, to our knowledge, to "n-order reactions". Therefore, it would be interesting to develop a general method for deconvoluting overlapping reactions without restrictions with regard to the kinetic model satisfied by the unit reactions.…”

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confidence: 99%

Discrimination of the kinetic model of overlapping solid-state reactions from non-isothermal data

Criado

González

Ortega

et al. 1988

Journal of Thermal Analysis

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A method has been developed that allows the deconvolution of up to 15 overlapping solidstate reactions without previous assumptions. Both the kinetic parameters and the reaction mechanisms fitted by the unit reactions can be determined from a series of non-isothermal experiments carried out at different heating rates.During recent years, the kinetic analysis of complex reactions has received the attention of a great number of authors [1][2][3][4]. Elder [5], Agrawall [6] and other workers have shown that the kinetic analysis of DTG or DTA traces obtained from the sum of a set of individual reactions leads to important errors in the determination of the activation energies. Ozawa [7] and Flynn [8] have analysed the effect of the heating rate on overlapping reactions in order to separate the individual steps. They have concluded that mutually independent reactions with large differences in activation energy can be deconvoluted by increasing or decreasing the heating rate. However, they cannot be separated if their activation energies are of the same order of magnitude. In such a case, the problem can only be resolved mathematically. It must be pointed out that a number of computer programs for deconvoiution have been proposed in the literature [9][10], but their application is restricted, to our knowledge, to "n-order reactions". Therefore, it would be interesting to develop a general method for deconvoluting overlapping reactions without restrictions with regard to the kinetic model satisfied by the unit reactions.Previous papers have shown [l l, 12] that non-isothermal curves of single solidstate reactions must satisfy the kinetic equations developed for the kinetic analysis of "n-order reactions", even if they follow a quite different mechanism. The values calculated for the apparent reaction order, n, and the ratio of the apparent n-order activation energy and the real one are included in Table 1. These data lead to the John Wiley & Sons, Limited, Chichester Akad~miai Kiad6, Budapest

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Meaningful activation energies for complex systems

Cited by 41 publications

References 17 publications

Comparison of the kinetics of conventional and microwave methyl methacrylate polymerization

Comparison of the kinetics of conventional and microwave methyl methacrylate polymerization

The kinetics of solid‐state reactions toward consensus, Part 2: Fitting kinetics data in dynamic conventional thermal analysis

Discrimination of the kinetic model of overlapping solid-state reactions from non-isothermal data

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