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

Abstract

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

Calculation of Kinetic Parameters of the Thermal Decomposition of Residual Waste of Coniferous Species: Cedrus Deodara

“…However, later on, this method has kept with group of methods, which evaluates the kinetic triplet at the single heating rate. Similarly, Criado and Ortega (1984) have also made conclusions on the drawbacks in their study and reported the detail calculation of the error in E occurred due to this assumption. In 1991, Flynn (1991) stated that f(X) follows a reaction model in which it varies according to n th power of remaining mass fraction:…”

Clarifications regarding the use of model-fitting methods of kinetic analysis for determining the activation energy from a single non-isothermal curve

“…The model providing the best linear fit is usually regarded as the correct one, and the activation energy is deduced from the slope of the fit. Unfortunately, it has been long established that the activation energy cannot be reliably determined from a single non isothermal curve because the experimental data almost always provides a reasonable fit regardless the kinetic model selected [3-5]. Despite that significant flaw, such inappropriate practice is still nevertheless widely used.…”

Activation Energy Determination in Case of Independent Complex Kinetic Processes

“…The model-based methods then include the non-fitting methods, such as master plots [14] and the method based on the compensation effect [15], or data-fitting methods, such as the combined kinetic analysis [16], the Koga method [17], or multivariate kinetic analysis (MKA; sometimes also called formal kinetic analysis) [18]. Whereas the functionality of all these methods is perfectly mapped and tested for the single kinetic processes, the theoretical testing of the behavior of these methodologies for the complex process scenarios is not very numerous and divided into rather occasional studies-see, e.g., [19][20][21][22][23][24][25][26][27]. Most of these papers provide qualitative testing of the considered methodologies in only few types of complex process situations.…”