Visualization of Structural Changes During Deactivation and Regeneration of FAU Zeolite for Catalytic Fast Pyrolysis of Lignin Using NMR and Electron Microscopy Techniques

Abstract

Catalytic fast pyrolysis of pretreated lignin (with hydrogen chloride solution) over FAU (15) zeolite uniquely yielded a high fraction of phenols, phenol alkoxys, and aromatic hydrocarbons. However, the zeolite underwent rapid deactivation. This paper reports the visualization of the structural changes during deactivation and regeneration of the zeolite is reported. The deactivated and regenerated zeolites were characterized by means of N 2 physisorption, electron microscopy, X-ray diffraction, magic angle spinning (MAS), and multiple quantum (MQ) nuclear magnetic resonance (NMR) techniques. The results indicated that, during catalyst deactivation, there was excessive coke deposition in the zeolite pore structure resulted in both pore blockage and active site poisoning. The coke was removed by calcination of the spent catalyst in air at high temperature > 550 8C which resulted in restoring the porosity and the activity to a large extent. However, the recovery of catalytic activity was incomplete attributing to irreversible structural changes in the catalyst during the deactivation and regeneration process. By fine-tuning the reaction conditions and the regeneration of the catalyst, the catalyst performance after reactivation was optimized. Catalyst regeneration after mild coke deposition (that is, after a few catalytic cycles) and mild oxidation conditions (low temperature and slow-heating ramp) are beneficial.

Catalytic Pyrolysis of Biomass and Polymer Wastes

“…The quick deactivation of zeolite Y was reported in CFP process of hydrogen chloride pretreated lignin [195]. SEM pictures showed heavy coke formation that blocked pore structures and poisoned the active sites of catalysts.…”

“…Ma et al [195] reported a FAU (SAR = 15) zeolite underwent a rapid deactivation in the pretreated lignin pyrolysis. During catalyst deactivation, there was excessive coke deposition in the zeolite pore structure resulted in both pore blockage and active site poisoning.…”

“…Catalyst deactivation by coke deposition is the major barrier in the catalytic pyrolysis of biomass and polymers. The coke can be removed by calcination of the spent catalyst in an oxygen-containing gas or water stream environment at high temperatures [195,254,272], which restores the porosity and activity to a large extent. However, recovery of catalytic activity may be incomplete and attributed to irreversible changes in catalyst structure that occur during the deactivation and/or regeneration processes [195,273].…”

Characterization of Metal‐zeolite Composite Catalysts: Determining the Environment of the Active Phase

“…The regeneration is done at 873 K for 5 h, as shown in Figure . The authors also find that to avoid deactivation, fewer pyrolysis cycles should be used prior to catalyst regeneration …”

Novel Micro-Mesoporous Composite ZSM-5 Catalyst for Aromatics Production by Catalytic Fast Pyrolysis of Lignin Residues

“…Aromatics can be used as raw materials for chemical industry and medicine, and as additives for aviation fuel. However, except for the economic advantages of CFP, there are also accompanying problems, such as rapid deactivation of conventional catalysts, low carbon yield, excessive PAHs production, which affects fuel quality, and the need for a higher catalyst to biomass (C/L) ratio for certain products [13][14][15].…”