(384b) A Combined Experimental and Modeling Study of Thermal and Non-Thermal Effects of Microwave-Assisted Direct Natural Gas Conversion to Value -Added Chemicals

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 presentation, we integrate microwave irradiation with heterogeneous catalysis to enable a higher methane conversion to C2 and aromatics at low temperature. The results show that methane conversion can reach 18% at 550 °C under microwave irradiation, while 800 °C is required to achieve the same level of conversion in a traditional fixed-bed reactor. The microwave irradiation facilitates heterogeneous catalysis process both thermally and non-thermally. Thermal effect, as known as “hot spots”, can be characterized experimentally, and the result indicates that the “hot spot” temperature can reach 800 °C while the bulk temperature stays 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. In this report, three-dimensional finite-element models based on Maxwell’s equations were developed to study the non-thermal effects of microwave irradiation on direct methane conversion process. The simulation results show the local ultra-high electric field exists between catalyst particles and at the metal-support boundary. With the existence of electric field between catalyst particles, stable methane molecules can be activated. The local high electric field at the metal-support boundary further facilitates the collapse of activated C-H bond and form C2, which is an important intermediate and product for this process. These field distributions explain the non-thermal effects of microwave-assisted catalytic chemical reactions, which significantly affect the final product distribution that higher C2 selectivity was observed in microwave reactor, and the intrinsic reaction pathway.