Determination of aerosol kinetics of thermal ZnO dissociation by thermogravimetry

Abstract

The thermal decomposition of ZnO is the high temperature solar step in a two-step water splitting process for sustainable H 2 production. To optimize aerosol solar reactor design, it is desired to understand the forward kinetics of this reaction in an aerosol configuration. Non-isothermal thermogravimetric (TG) experiments were conducted to determine the applicability of TG kinetic data to aerosol reactor environments. It was found that the differentiating heat and mass transfer factors—initial loaded mass, particle size, and heating rate—had no statistically significant effect on the activation energy or pre-exponential factor. This allowed TG data to be applied to the aerosol case. Isothermal TG experiments were subsequently performed to determine the kinetic rate parameters. Using the model expression d α d t = k * e E a / R ( 1 / T - 1 / T 0 ) ( 1 - α ) 2 / 3 , with T 0 = 1895 K , E a was found to be 353 ± 25.9 kJ / mol , and k * was found to vary inversely with diffusion distance in the TG crucible. The specific rate constant for a diffusion distance of 1 in was k 0 = 3.15 × 10 6 ± 5.54 × 10 5 s - 1 . Both of these results are in agreement with L’vov theory, and a simple electrostatic dissociation mechanism was proposed.