A combined experimental and modeling study of Microwave-assisted methane dehydroaromatization process

Abstract

The challenges in direct methane conversion to higher-value chemicals include rapid catalyst deactivation and comparatively low single-pass conversion. The most important step in direct methane conversion is the activation of strong C–H bonds. In this paper, we integrated microwave irradiation with heterogeneous catalysis to enable a higher methane conversion to C2 and aromatics at low temperature. The results showed that the methane conversion can reach 18% at 550 °C under microwave irradiation, while a temperature higher than 800 °C was required to achieve the same level of methane conversion in a traditional fixed-bed reactor. The microwave irradiation may facilitate this heterogeneous catalysis process both thermally and non-thermally. Thermal effect, as known as “hot spots”, can be characterized experimentally. The results indicated the “hot spot” temperature can reach as high as 800 °C while the bulk temperature stayed at 550 °C. However, the non-thermal effect is difficult to characterize due to the limitations of existing in-situ instrumentations. Finite-element modeling can be a powerful engineering tool to simulate and understand complex physic fields. The simulation results show that between spherical catalyst particles the electric field on the catalyst bed was at a level of 104 V/m and the non-uniform electric field distribution on the catalyst bed. Under this level of external electric field, methane activation on the catalyst surface was possible. These field distributions can explain the non-thermal effects of microwave-assisted catalytic chemical reactions, supported by the observation of benzene hydrogenolysis side reaction. With the thermal and non-thermal effects from microwave irradiation, microwave-assisted heterogeneous catalytic process can be an attractive solution to activate stable feedstock molecules and can be applied to direct methane conversion process.