Determination of Density Distribution Functions of the Apparent Activation Energies for Nonisothermal Decomposition Process of Sodium Bicarbonate Using the Weibull Probability Function

The procedure for the determination of density distribution functions of the apparent activation energies (ddfE _a s), for the nonisothermal decomposition process of sodium bicarbonate under a nitrogen atmosphere was established. It was found that the experimental integral and differential conversion curves at different heating rates can be successfully described by the nonisothermal Weibull distribution function (Wdf), in wide range of the degree of conversion (α = 0.15 to 0.98). It was established that the Weibull distribution parameters (β and η) show the different dependences on the heating rate of the system (v _h ). It was found that the rate equation, expressed through the Weibull (nonisothermal) probability density function (Wpdf), can be used for the description of the sodium bicarbonate decomposition process under dynamic conditions. It was also established that the skewness of the Wpdf shows negative values and increases with an increase in the heating rate, but stays below the zero point. By applying the model independent (Friedman) method, the complex dependence of apparent activation energy (E _a ) on the degree of conversion (α) was established. It was shown that in the conversion range of 0.25 ≤ α ≤ 0.95, the E _a is practically constant (95.4 kJmol⁻¹). It was concluded that the calculated ddfE_as are dependent on the heating rate of the system. The heating rate has the influence on the skewness of the Wpdfs, but does not change the reaction profile of the considered decomposition process. The complex dependence between the kinetic parameters (A and E _a ) for the considered decomposition process was established. The evaluated ddfE _as show that the investigated decomposition process follows the same reaction mechanism, i.e., the two-parameter Šesták–Berggren (SB) reaction model. Also, it was concluded that such behavior leads to the complex dependence of E _a on the degree of conversion (α), and this dependence is a natural consequence of the existence of the distribution of E _a .