Single Non-isothermal Curve Research Articles

A New Look at Kinetics in Relation to Food Storage.

Modern mathematical software and user-friendly interactive programs can simplify and speed up kinetics calculations. They also open the way for new approaches to storage data gathering and analysis. This is demonstrated with a recently introduced simple exponential model that is interchangeable with the Arrhenius equation and endpoints and successive points methods and that estimates chemical degradation kinetics parameters from a small number of isothermal or nonisothermal experimental data. Also presented are a method to determine shelf life using two chemical markers and a global phenomenological model for peaked reactions, such as those encountered in lipid oxidation. Also recently introduced are freely downloadable Wolfram Demonstrations and other interactive software to generate, visualize, examine, and/or compare actual or hypothetical storage scenarios in minutes. They include programs that solve pairs of simultaneous nonlinear algebraic or differential rate equations by passing two reconstructed degradation curves, or a single nonisothermal curve, through two entered experimental points by moving the degradation parameters' sliders on the screen.

Comments on “Pyrolysis kinetics of biomass from product information” (Applied Energy 110 (2013) 1–8) regarding the inability to obtain meaningful kinetic parameters from a single non-isothermal curve

In this letter, some widespread misuses pertaining to kinetic analysis carried out using experimental data from a single non-isothermal curve are clarified in response to a manuscript recently published in this journal (Huang et al., 2003). It is shown that kinetic parameters cannot be unambiguously determined from data extracted from a single non-isothermal curve because different kinetic triplets can describe the very same curve. Thus, a set of curves recorded under different heating schedules are to be employed in order to obtain reliable kinetic parameters. Also, it is proven that assuming first order kinetic models constitutes an oversimplification that can easily lead to erroneous kinetic parameters.

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

BackgroundThis paper provides some clarifications regarding the use of model-fitting methods of kinetic analysis for estimating the activation energy of a process, in response to some results recently published in Chemistry Central journal.FindingsThe model fitting methods of Arrhenius and Savata are used to determine the activation energy of a single simulated curve. It is shown that most kinetic models correctly fit the data, each providing a different value for the activation energy. Therefore it is not really possible to determine the correct activation energy from a single non-isothermal curve. On the other hand, when a set of curves are recorded under different heating schedules are used, the correct kinetic parameters can be clearly discerned.ConclusionsHere, it is shown that the activation energy and the kinetic model cannot be unambiguously determined from a single experimental curve recorded under non isothermal conditions. Thus, the use of a set of curves recorded under different heating schedules is mandatory if model-fitting methods are employed.

A unified theory for the kinetic analysis of solid state reactions under any thermal pathway

The Ozawa concept of generalized time has been used for developing master plots for the different kinetic models describing solid state reactions. These plots can be indistinctly used for analysing isothermal or non-isothermal experimental data. It is demonstrated that it is not possible to discriminate the kinetic model from a single non-isothermal curve without a previous knowledge of the activation energy. However, it has been shown that the ln [(da/dt)/f(a)] data taken from a set of DTG curves obtained at different heating rates lie on a single straight line when represented as a function of 1/T only if the kinetic model really obeyed by the reaction is considered. Moreover, the true values of E and A are obtained from the slope and the intercept of this straight line.

Numerical data for the evaluation of kinetic parameters of solid state decompositions by the non-isothermal method

Determination of the kinetic parameters of the thermal decomposition of solids usually requires a knowledge of the function g(α), describing the mechanism of decomposition. An effective and fast method is described for the determination of kinetic parameters from a single non-isothermal curve. Numerical data in the form of a ready reference table are given from which the kinetic parameters can be obtained once the correct form of g(α) has been established.

Applicability of the master plots in kinetic analysis of non-isothermal data

The ability to determine the actual reaction mechanism (RM) of solid state processes from a single non-isothermal curve was analysed and discussed. Owing to the correlation of all kinetic parameters the RM cannot be ascertained without the knowledge of activation energy. However, if the activation energy is known a simple and precise method for the determination of RM can be proposed. The method was used to analyse the experimental data of the thermal decomposition of magnesium carbonate in vacuum. It was found that the reaction follows the R3 mechanism which is in very good agreement with the results of isothermal experiments.