Complex Crystallization Kinetics of a Mg-Al Hydrotalcite and Their Practical Implications from the Process Point of View.

Marco-Antonio López-Martínez,Ignacio Melián-Cabrera

doi:10.1021/acs.iecr.1c01785

Abstract

Hydrotalcites are an important class of layered materials, displaying ion-exchange, adsorption, and base catalytic properties. The crystallization kinetics for hydrotalcites are however hardly available. Nevertheless, as their reconstruction from the oxides (also called as “memory effect”) is considered a synthesis route, this can be used to study the crystallization phenomena. This note looks at the reconstruction kinetics of a Mg–Al hydrotalcite using previously reported kinetic expressions. It was found that high temperature is beneficial if the process is controlled by nucleation. The temperature effect is less obvious when the process reaches a diffusional control regime. For example, temperature is beneficial to shorten the processing time in a nucleation-regime conversion (e.g., 40%). However, to achieve a high conversion (e.g., 98–99%), an intermediate temperature shows the optimal condition, i.e., shortest processing time. The work shows useful side effects of diffusional control. It also highlights the importance of obtaining the kinetics over the entire range for process optimization and, finally, emphasizes that both parameters in the Avrami–Erofe’ev model impact the time required to achieve a given conversion. Directions for further studies to understand the kinetic-process relationships have been highlighted.

Highlights

Hydrotalcites are an important class of layered materials, displaying ion-exchange, adsorption, and base catalytic properties
Hydrotalcites are layered materials that find applications in the pharmaceutical industry, plastic processing as a stabilizer, catalysis, ion exchange, and adsorption.[1−5] In heterogeneous catalysis, hydrotalcites or activated hydrotalcites are effective in reactions such as aldol condensation,[6,7] Claisen−Schmidt condensation,[8] and glycerol carbonate synthesis,[9,10] to cite a few
It can be seen that heating the solid has a minor impact, due to the lower heat capacity of the solid. Based on these high energy figures, we looked at the temperature effect on the crystallization to understand what the optimal temperature is and to reduce heating costs

Summary

Introduction

Hydrotalcites are an important class of layered materials, displaying ion-exchange, adsorption, and base catalytic properties. Based on these high energy figures, we looked at the temperature effect on the crystallization to understand what the optimal temperature is and to reduce heating costs.

Results

Conclusion