Comparison of Microwave and Radio-Frequency Heating of Dealuminated Zeolites and Al2O3

Abstract

In the present study, the dielectric heating option was investigated for various dry materials: USY zeolite, ZSM-5 zeolite, and α- & γ-alumina. These materials are characterized by low effective dielectric loss factors; therefore they are often considered as not accessible for direct dielectric heating. Applying technically relevant volumes up to 20 L, dielectric heating could be demonstrated for all these materials when employing radio waves (RW) whereas heating with microwaves (MW) was difficult or even impossible. Dielectric heating experiments were also simulated with the CST electromagnetic simulation software.It could be shown that for all tested materials RW heating is more suitable than MW heating with regard to heating rates, temperature rise (both at equal power input) and homogeneity of the temperature pattern. The comparison of experimental data and simulation shows an excellent agreement. Thus, dielectric heating utilizing frequencies in the MHz range (radio-frequencies, RF) was demonstrated to be well applicable, even for materials with low loss factors, up to technically relevant temperatures and scales.This study also includes the evaluation of the energy efficiency for RW heating on the basis of the heating and power input data. Reasons for lower efficiencies, even under optimal fitting conditions applying an electronic matching network, are discussed and interpreted using literature and own experimental results, namely temperature-programmed desorption (TPD).