Impact of the Framework Type on the Regeneration of Coked Zeolites by Non-Thermal Plasma in a Fixed Bed Dielectric Barrier Reactor

Amir Astafan,Ludovic Pinard,Alexander Sachse,Catherine Batiot-Dupeyrat

doi:10.3390/catal9120985

Abstract

The formation of coke as a result of propene transformation at 623 K on zeolites results from a product shape selectivity mechanism of which the products are polyaromatic molecules, such as pyrene on MFI, anthracene on MOR, pyrene and coronene on FAU. Zeolite regeneration can be achieved by using non-thermal plasma (NTP), with decreased energy consumption, employing a fixed bed dielectric barrier reactor. The efficiency of this alternative regeneration process depends on the coke toxicity. On MFI and FAU (featuring three-dimensional 10 and 12 ring channel systems, respectively) coking occurs by poisoning the Brønsted acid sites; on MOR, (presenting a one-dimensional 12 ring channel system) pore blocking takes place, leading to higher coke toxicity. A complete coke removal is achieved on MFI and FAU zeolites using NTP within 3 h, while for MOR coke, removal proceeds slower and is incomplete after 3 h on stream. Hence, the efficiency of regeneration is impacted by the accessibility of active oxygenated species generated under plasma (e.g., O*, O2+) to coke molecules.

Highlights

The main cause of acidic zeolite deactivation is carbon deposition, which poisons or blocks the accessibility of reactants to active sites [1]
We have recently shown that coke combustion assisted by non-thermal plasma (NTP) is a valuable alternative to classical thermal treatments; allowing for total regeneration of zeolite catalysts at room temperature [28,29,30,31]
It was observed that the efficiency of coke oxidation by non-thermal plasma is very sensitive to both the coke nature and its toxicity

Summary

Introduction

The main cause of acidic zeolite deactivation is carbon deposition (coke), which poisons or blocks the accessibility of reactants to active sites [1]. Such deactivation and the associated regeneration of catalysts represent a major financial burden and important environmental costs for industrial processes. The chemical composition of coke depends on the reaction conditions (temperature, contact time and time-on-stream) [1,2,3,4,5] and on the aging treatment [6,7]. The H/C coke ratio retained within zeolite micropore reaches a value of almost

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