A kinetic study of the thermal decomposition process of potassium metabisulfite: Estimation of distributed reactivity model
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The thermal decomposition kinetics of potassium metabisulfite was studied by thermogravimetric (TG) and differential thermogravimetric (DTG) techniques using non-isothermal experiments. The apparent activation energy (E-a) is determined using the differential (Friedman) isoconversional method. The results of the Friedmans isoconversional analysis of the TG data suggests that the investigated decomposition process follows a single-step reaction and the observed apparent activation energy was determined as 122.4 +/- 2.1 kJ mol(-1). A kinetic rate equation was derived for the decomposition process of potassium metabisulfite with contracting area model, f(alpha) = 2(1-alpha)(1/2), which is established using the Maleks kinetic procedure. The value of pre-exponential factor (A) is also evaluated and was found to be A = 1.37 x 10(12) min(-1). By applying the Miuras procedure the distributed reactivity model (DRM) for investigated decomposition process was established. From the dependence alph...a versus E-a, the experimental distribution curve of apparent activation energies, f(E-a), was estimated. By applying the non-linear least-squares analysis, it was found that the Gaussian distribution model (with distribution parameters E-0 = 121.3 kJ mol(-1) and sigma = 1.5 kJ mol(-1)) represents the best reactivity model for describing the investigated process. Using the Miuras method, the A values were estimated at five different heating rates and the average A values are plotted against E-a. The linear relationship between the A and E-a values was established (compensation effect). Also, it was concluded that the E-a values calculated by the Friedmans method and estimated distribution curve, f(E-a), are correct even in the case when the investigated decomposition process occurs through the single-step reaction mechanism. (C) 2008 Elsevier Ltd. All rights reserved.
Keywords:inorganic compounds / thermogravimetric analysis (TGA) / surface properties
Source:Journal of Physics and Chemistry of Solids, 2008, 69, 8, 1923-1933
- Ministry of Science and Environmental Protection of Serbia [142025, 142047, 142050]