Authors:Aysel Kantürk Figen, Osman İsmail, and Sabriye Pişkin
kinetic models. In the present study, devolatilization non-isothermalkinetic analysis of agricultural stalks and application of TG-FT/IR analysis were investigated. Stalks of agricultural materials, sunflower, rice, corn, and wheat, are abundant in Edirne
Authors:Evaneide Lima, Marisa Crespi, C. Ribeiro, and Sonia de Almeida
Leachate samples from a sanitary landfill of Araraquara city and composting usine of Vila Leopoldina, São Paulo, Brazil were
lyophilized to remove the water content. TG/DTG curves at different heating rates were recorded. The second step of the thermal
decomposition of leachate from the Araraquara landfill (CB1), from the composting usine from Vila Leopoldina (CB2) from the organic phase extracted (FO) and aqueous phase (FA) were all kinetically evaluated using the non-isothermal method.
By Flynn-Wall isoconversional method the following values were obtained: E=234±3.65 kJ mol−1 and logA=29.7±0.58 min−1 for CB1; E=129±1.66 kJ mol−1 and logA=11.8±0.10 min−1 for CB2; E=51.6±1.35 kJ mol−1 and logA=6.09±0.09 min−1 for FO and E=76.91±6.33 kJ mol−1 and logA=8.88±0.7 min−1 for FA with 95% confidence level. Applying the procedures of Málek and Koga, SB kinetic model (Šesták-Berggren) is the most
appropriate to describe the decomposition of CB1, CB2, FO and FA.
A new method is reported for the evaluation of non-isothermal kinetic data for various forms of the conversion function. The
algorithm is based on a pseudo-inverse matrix method. A description of the algorithm and some calculation examples are presented.
A differential method is proposed which uses local heating rates to evaluate non-isothermal kinetic parameters. The method
allows to study the influence of the deviation of the true heating rate with respect to the programmed one on the values of
the kinetic parameters. For application, the kinetic parameters of the following solid-gas decomposition reaction were evaluated:
[Ni(NH3)6]Br2(s)→[Ni(NH3)2]Br2(s)+4NH3(g). The results obtained revealed significant differences between the values of the non-isothermal kinetic parameters obtained
by using local heating rates and those obtained by using the programmed heating rate. It was also demonstrated that the kinetic
equation which makes use of the local heating rates permits a better description of the experimental (α, t) data than the
kinetic equation which uses the programmed constant heating rate.
A method is proposed for evaluation of the activation parameters for reactions which occur under non-isothermal conditions.
This method can discriminate between possible differential conversion functions. The proposed method, which was coded into
a software package available to the scientific community, is designed to solve an overdetermined systems of equations: dai/dt=k(Ti)f(ai) where i equations are to be considered (i can be the number of experimental points). Solution of this overdetermined system
with a pseudo-inverse matrix method furnishes the activation parameters and the parameters of the conversion function f(a).
Some examples of application of this method in non-isothermal kinetic analysis are presented.
An improved version of the Coats-Redfern method of evaluating non-isothermal kinetic parameters is presented. The Coats-Redfern approximation of the temperature integral is replaced by a third-degree rational approximation, which is much more accurate. The kinetic parameters are evaluated iteratively by linear regression and, besides the correlation coefficient, the F test is suggested as a supplementary statistical criterion for selecting the most probable mechanism function. For applications, both non-isothermal data obtained by theoretical simulation and experimental data taken from the literature for the non-isothermal dehydration of Mg(OH)2 have been processed.
A program for the evaluation of non-isothermal kinetic parameters is presented. The program allows evaluation of the kinetic
parameters under constant heating rate or constant reaction rate conditions. The simulation of temperature vs. conversion
curves is also possible. A regression method is included, which allows a discrimination between various conversion functions
and also evaluation of the activation parameters.
The program was tested with various simulated decomposition curves and the non-isothermal decomposition curves of calcium
oxalate. The program is written in Visual BASIC 4.0 and can be run under Windows 95 .