Effects of Particle Size on the Kinetics of Physico-geometrical Consecutive Reactions in Solid–Gas Systems: Thermal Decomposition of Potassium Hydrogen Carbonate

Abstract

In this study, we investigated the mechanisms of variations in the overall kinetic behavior of the physico-geometrical consecutive process of the surface reaction (SR) and phase boundary-controlled reaction (PBR) in solid−gas systems with varying particle size of the reactants. Thermal decomposition of potassium hydrogen carbonate (KHCO 3 ) was selected as a suitable model reaction owing to the significant changes in its kinetic behavior with particle size and less sensitivity to experimental conditions for recording kinetic data. The reaction was characterized by an induction period (IP) accompanied by the formation of a gelatinated surface layer. The subsequent mass-loss process was indicated by the consecutive SR and PBR, which was accompanied by the nucleation and growth of solid products in the gelatinated layer and inward advancement of the reaction interface, respectively. Formal kinetic analyses of systematically recorded kinetic data revealed variations in the overall kinetic behaviors with the sample particle size, including changes in the variation trend of isoconversional activation energy values as the reaction progressed and the shape of the experimental master plot. The kinetics of each reaction step in the physico-geometrical consecutive process was investigated using an advanced kinetic approach based on an IP−SR−PBR model. The results revealed variations in the overall kinetic behaviors of the thermal decomposition of KHCO 3 with particle size, owing to changes in the reactivity of the reactant surface in IP, overlapping degree of SR and PBR, and total migration length of the reaction interface in PBR.

Physico-geometrical kinetics of the thermal dehydration of sodium carbonate monohydrate as a compacted composite of inorganic hydrate comprising crystalline particles and matrix

“…3(b)), a systematic increase in the reaction initiation temperature was observed with increasing β value, representing typical behavior for the thermal decomposition of solids accompanied by an IP. 10,52–55 The mass loss curves were also shifted to higher temperatures with increasing β value. Irrespective of the β value, a shoulder was observed in the initial acceleration stage before the maximum mass loss rate was achieved.…”

“…4(b)). The temperature dependence of the average rate of the IP, expressed by the reciprocal of t IP , is given in the following an Arrhenius-type equation: 10,52–57 where A IP and E a,IP are the Arrhenius parameters of the preexponential factor and activation energy of the IP, respectively, and R is the gas constant. The changes in the rate of the IP as the fractional conversion ( α IP ) increased are expressed by the function f IP ( α IP ).…”

“…56 In the other case, the Arrhenius-type plot of ln(1/t IP ) versus T À1 should be understood as an isoconversional plot, based on the assumption that the a IP value at 1/t IP is invariant among the IP processes at different temperatures. 10,[52][53][54][55] In the latter case, the intercept of the Arrhenius-type plot should be expressed as ln[A IP Áf IP (a IP )]. The Arrhenius-type plot for the IP exhibited a statistically significant linear correlation with a correlation coefficient of g = À0.9937 (Fig.…”

“…5,6 The steady energy supply to the reaction interface via thermal conduction through the surface product layer is disturbed by the enthalpy change resulting from the reaction at the reaction interface, which causes a self-heating or self-cooling effect on the interfacial reaction kinetics. 7,8 Therefore, the apparent kinetics of the thermal decomposition in a welldefined single reactant body vary with the sample shape and size, 9,10 as well as the reaction conditions.…”

An advanced kinetic approach to the multistep thermal dehydration of calcium sulfate dihydrate under different heating and water vapor conditions: kinetic deconvolution and universal isoconversional analyses

“…3(a)), as generally observed for the thermal decomposition of solids. 2,3,31,46–52 The exponential curves at each p (H 2 O) value shifted to higher temperatures as the p (H 2 O) value increased. In the conventional kinetic description based on the Arrhenius-type temperature dependence without considering the effect of p (H 2 O), the temperature dependence of the IP process at each p (H 2 O) value is expressed using the reciprocal t IP as an average rate: 53–55 where A IP and E a,IP are the Arrhenius pre-exponential factor and activation energy for the IP, respectively.…”