Abstract
Microwave-assisted heterogeneous catalysis (MHC) is gaining attention due to its exciting prospects related to selective catalyst heating, enhanced energy-efficiency, and partial inhibition of detrimental side gas-phase reactions. The induced temperature difference between the catalyst and the comparatively colder surrounding reactive atmosphere is pointed as the main factor of the process selectivity enhancement towards the products of interest in a number of hydrocarbon conversion processes. However, MHC is traditionally restricted to catalytic reactions in the absence of catalyst coking. As excellent MW-susceptors, carbon deposits represent an enormous drawback of the MHC technology, being main responsible of long-term process malfunctions. This work addresses the potentials and limitations of MHC for such processes affected by coking (MHCC). It also intends to evaluate the use of different catalyst and reactor configurations to overcome heating stability problems derived from the undesired coke deposits. The concept of long-term MHCC operation has been experimentally tested/applied to for the methane non-oxidative coupling reaction at 700 °C on Mo/ZSM-5@SiC structured catalysts. Preliminary process scalability tests suggest that a 6-fold power input increases the processing of methane flow by 150 times under the same controlled temperature and spatial velocity conditions. This finding paves the way for the implementation of high-capacity MHCC processes at up-scaled facilities.
Highlights
Microwave-assisted heating has emerged as an energy-efficient heating solution for a number of processes involving chemical transformations [1,2,3,4,5,6,7,8]
We explore different catalyst arrangement and reactor configuration strategies to overcome the limitations posed by coke deposition in MW-assisted heterogeneous catalytic processes
This work assessed the use of MW-assisted heating equipment for heterogeneous catalytic process affected by coking
Summary
Microwave-assisted heating has emerged as an energy-efficient heating solution for a number of processes involving chemical transformations [1,2,3,4,5,6,7,8]. Microwave (MW) irradiation has exciting prospects for gas–solid heterogeneous catalysis, since the selective dielectric heating of suitable catalytic materials is capable to establish a significant gas–solid temperature gradient between the heated catalytic sample and the comparatively colder surrounding gas [9,10,11]. The application of microwave-assisted heating to catalytic systems that operate in the absence of oxygen is, challenging due to the formation of coke deposits on the catalyst surface This causes a fast deactivation of the catalyst and significant stability issues. Coke deposits may disturb the electromagnetic field within the resonator leading to cavity uncoupling and causing the instantaneous decrease of the catalytic sample temperature, extinguishing the catalytic process [15,16]
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