(685g) Numerical Modeling of Microwave-Assisted Catalytic Conversion of Natural Gas: The Role of SiC and Coke Deposition on Microwave Absorption

Natural gas flaring is a cheap method to process the stranded natural gas due to limited pipeline takeaway capacity. However, flaring is not only a significant waste of domestic resources but also produces significant greenhouse gas emissions. Converting the excess natural gas to value-added chemicals is a way to monetize this wasted resource. Zeolite-based catalysts are widely applied to this direct conversion process. An integrated microwave catalyst system has been demonstrated to be capable of C-H bond activation for direct methane conversion. However, the microwave sensitivity of the zeolite is poor, therefore, a microwave absorber like silicon carbide (SiC), either in the form of particles additive or monolith, offers a viable way to enhance microwave heating. This study presents a computational perspective of the performance of the SiC microwave absorber in proximity to the zeolite catalyst in two different configurations, 1) SiC and catalyst powders co-mixed and 2) catalyst poured in the channels of the SiC monolith, and discusses the influence of the observed reaction performance in the microwave reactor.

The results show that a catalyst-filled SiC monolith structure provides a more homogeneous heating pattern under the same power setting compared to catalyst-SiC powder mixture case. However, the monolith wall creates more than 30% of electric field decay per monolith channel, which affects the potential activation of the intermediates triggered by the moderate electric field intensity. Coking is the biggest causes of catalyst deactivation. It is observed experimentally that the catalyst deactivation rate is higher in the microwave reactor. The numerical simulation results show that the existence of coke will significantly and negatively affect the electric field strength around the catalyst.Since coke is a good microwave absorber, the coke absorbs microwave energy quickly and causes temperature overshot of the catalyst bed, which results in damage to the zeolite structure.