Catalytic Fast Pyrolysis of Biomass: Catalyst Characterization Reveals the Feed-Dependent Deactivation of a Technical ZSM-5-Based Catalyst

Abstract

Catalyst deactivation due to coking is a major challenge in the catalytic fast pyrolysis (CFP) of biomass. Here, a multitechnique investigation of a technical Al2O3-bound ZSM-5-based extrudate catalyst, used for the CFP of pine wood and cellulose (at a reactor temperature of 500 °C), provided insight into the effects of extrusion, the catalytic pyrolysis process, and catalyst regeneration on the catalyst structure. As a result of a reduction in acidity and surface area due to the coking catalyst, the activity dropped drastically with increasing time-on-stream (TOS), as evidenced by a decrease in aromatics yield. Strikingly, confocal fluorescence microscopy at the single-particle level revealed that vapor components derived from whole biomass or just the cellulose component coke differently. While pine-wood-derived species mainly blocked the external area of the catalyst particle, larger carbon deposits were formed inside the catalyst’s micropores with cellulose-derived species. Pyridine FT-IR and solid-state NMR spectroscopy demonstrated irreversible changes after regeneration, likely due to partial dealumination. Taken together with <30 g kg–1 aromatics yield on a feed basis, the results show a mismatch between biomass pyrolysis vapors and the technical catalyst used due to a complex interplay of mass transfer limitations and CFP chemistry.

Catalytic Fast Pyrolysis of Lignocellulosic Biomass to Benzene, Toluene, and Xylenes

“…A "technical catalyst" such as extruded Al 2 O 3 -HZSM-5 was explored in CFP of pine wood and cellulose at 500 °C [44]. The focus of the study was on effect of pyrolysis temperature.…”

“…An extruded HZSM-5 (a.k.a. "technical catalyst") containing an alumina binder was also examined in its deactivation in ex situ CFP of cellulose and pinewood [44]. CFP of cellulose generates smaller oxygenates, which diffused into the zeolite to produce a "catalytic coke", made via a ring-growth mechanism involving H-transfer at temperatures above 200 °C [123].…”

Production of Gasolines and Monocyclic Aromatic Hydrocarbons: From Fossil Raw Materials to Green Processes

“…While solid catalysts may improve product yield, their quite rapid deactivation [204] makes necessary a frequent regeneration step. Coking is a likely main cause of deactivation, and can be reversed by coke combustion.…”

“…As an alternative, hydrotreating sulfide catalysts, such as Co-Mo sulfides, can also be used. Moreover, catalysts for bio-oil upgrading tend to deactivate by coking; thus, regeneration steps are needed [204]. 6.5.5.…”

Biorefinery via Catalytic Upgraded Fast Pyrolysis of Biomass

“…Catalytic upgrading of pyrolysis (CFP) vapours can be carried out either in-situ pyrolysis step or ex-situ catalytic step. In-situ CFP pyrolysis and catalytic upgrading occurring in a one-step with a single reactor process, while in ex-situ CFP it is required a transfer of the pyrolysis vapours from the initial pyrolysis reactor to a secondary reactor for catalytic upgrading [13][14][15][16][17][18].…”