Kinetic Modeling of the Thermal Decomposition of Zinc Sulfate Through a Global Optimization Method

Abstract

The thermal decomposition of zinc sulfate is a highly relevant process, as the final product (zinc oxide) has a great number of applications. Moreover, the process itself can be used for hydrogen production in thermochemical water-splitting cycles. The present manuscript proposes a different approach over the modeling of the decomposition reaction, using particle swarm optimization (PSO) to estimate the kinetic parameters (pre-exponential factor, activation energy, and reaction order). Thermodynamic simulations have been performed to evaluate the influence of the partial pressure of ${\text{SO}}_{3}$ and the temperature in the equilibrium of the system was made. The thermogravimetric runs were performed in a non-isotherm condition using inert atmosphere. The results indicate that the decomposition takes place in two different stages: zinc sulfate decomposes into ${\text{ZnO}}\cdot 2{\text{ZnSO}}_{4}$, which is further decomposed into zinc oxide. The reactions involved can occur simultaneously, as enough ${\text{ZnO}} \cdot 2 {\text{ZnSO}}_{4}$ is formed by the decomposition of ${\text{ZnSO}}_{4}$. The model showed an excellent agreement with the experimental data, with pre-exponential factor equal to 2.52$\times 10^{12}$ and 1.25$\times 10^{16}$ min$^{-1}$, activation energy of 272 and 367 kJ mol$^{-1}$, and reaction order of 2.0 and 1.0, for the thermal decomposition of ${\text{ZnSO}}_{4}$ and ${\text{ZnO}}\cdot 2{\text{ZnSO}}_{4}$, respectively. The activation energy values found in the present work are in the same range as the ones found in previous literature studies.