Reduction of metal oxides using thermogravimetry under microwave irradiation

Satoshi Fujii,Hirotsugu Takizawa,Naoto Haneishi,Masahiro Yamamoto,Shuntaro Tsubaki,Yuji Wada,Jun Fukushima

doi:10.1063/5.0050907

Abstract

Chemical reactions performed under microwave irradiation often demonstrate high reaction rates, high selectivity, and low reaction temperatures, which allows for more compact reactors and more energy-efficient processes than used in conventional heating methods. In this study, we discovered a new chemical reaction and proposed a new material synthesis method, performed using a solid-state microwave source with an oscillator and a single-mode cavity. We developed a microwave heating thermogravimetry apparatus to confirm that microwave irradiation reduced the temperature of the reduction process. Next, we applied this apparatus to the reduction process of copper oxide with carbon as the reducing agent and compared microwave heating with conventional heating. We demonstrated that the reduction temperature of microwave heating was 192 °C in a magnetic (H) field and 265 °C in an electric (E) field, which were lower than those of conventional heating. For microwave heating in the E-field, plasma strongly affected the reaction process, leading to a reduction in the reaction temperature. For microwave heating in the H-field, localized heating occurred and the average reaction temperature was lower. Using the obtained results, an applicator suitable for these modes can be designed, enabling a reduction process with an additional energy-saving effect.

Highlights

Application of microwaves to chemical reactions has the potential to improve the efficiency and save energy of chemical processes and reduce the environmental burden
Chemical reactions performed under microwave irradiation often demonstrate high reaction rates, high selectivity, and low reaction temperatures, which allows for more compact reactors and more energy-efficient processes than used in conventional heating methods
We developed a microwave heating thermogravimetry apparatus to confirm that microwave irradiation reduced the temperature of the reduction process

Summary

INTRODUCTION

Application of microwaves to chemical reactions has the potential to improve the efficiency and save energy of chemical processes and reduce the environmental burden. Haneishi et al reported the phenomenon of forming a localized high-temperature region at the vicinal contact points of catalyst particles when microwave heating was applied to a chemical reaction of a solid catalyst packed bed. This could not be obtained by the conventional heating method.. Several studies have shown that the reduction of iron, scandium, and magnesium oxides is effective under microwave irradiation.10–15 They demonstrated that the energy efficiency of microwave irradiation is higher and the degree of the reduction reaction is lower than those of conventional heating. The use of this device allows the verification of the temperature at which the reduction of the metal oxide occurs

EXPERIMENTAL

AND DISCUSSION

CONCLUSION