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Mechanism and Kinetic of Coke Oxidation by Nonthermal Plasma in Fixed-Bed Dielectric Barrier Reactor

Astafan, A., Batiot-Dupeyrat, C., Pinard, L.
Journal of physical chemistry 2019 v.123 no.14 pp. 9168-9175
Bronsted acids, acidity, catalysts, combustion, energy, geometry, micropores, naphthalene, physical chemistry, propylene, zeolites
The formation of coke resulting from propene transformation at 623 K on a faujasite zeolite occurs according to a product shape selectivity mechanism and yields to the formation of highly alkylated polyaromatic molecules such as naphthalene, pyrene, and coronene. Their main parts are trapped in the inner cavities (supercages), poison Brønsted acid sites, and plug micropores. With a common thermal regeneration process, coke burns at 800 K, whereas this study shows that a complete regeneration of zeolite (i.e., total recovery of the native acidity and microporosity) can be achieved at 293 K by using a nonthermal plasma with a low energy consumption in a fixed-bed dielectric barrier reactor: a geometry suitable for industrial scaling. The kinetic rates of coke oxidation and the recovery of acidity and microporosity are similar. The active species (e.g., O*, O₂⁺) are able to diffuse within the zeolite micropores and oxidize the light molecules, 36 times faster than the heavier ones. Thanks to a complete characterization of both the regenerated catalyst and the remaining coke molecules, a reaction scheme is proposed. We claim that catalyst regeneration assisted by nonthermal plasma is a real alternative to thermal combustion.