Catalytic Fast Pyrolysis of Kraft Lignin With Conventional, Mesoporous and Nanosized ZSM-5 Zeolite for the Production of Alkyl-Phenols and Aromatics.

Polykarpos A Lazaridis,Stamatia A Karakoulia,Konstantinos S Triantafyllidis,Apostolos P Fotopoulos

doi:10.3389/fchem.2018.00295

Polykarpos A Lazaridis, Stamatia A Karakoulia + Show 2 more

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https://doi.org/10.3389/fchem.2018.00295

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Abstract

The valorization of lignin that derives as by product in various biomass conversion processes has become a major research and technological objective. The potential of the production of valuable mono-aromatics (BTX and others) and (alkyl)phenols by catalytic fast pyrolysis of lignin is investigated in this work by the use of ZSM-5 zeolites with different acidic and porosity characteristics. More specifically, conventional microporous ZSM-5 (Si/Al = 11.5, 25, 40), nano-sized (≤20 nm, by direct synthesis) and mesoporous (9 nm, by mild alkaline treatment) ZSM-5 zeolites were tested in the fast pyrolysis of a softwood kraft lignin at 400–600°C on a Py/GC-MS system and a fixed-bed reactor unit. The composition of lignin (FT-IR, 2D HSQC NMR) was correlated with the composition of the thermal (non-catalytic) pyrolysis oil, while the effect of pyrolysis temperature and catalyst-to-lignin (C/L) ratio, as well as of the Si/Al ratio, acidity, micro/mesoporosity and nano-size of ZSM-5, on bio-oil composition was thoroughly investigated. It was shown that the conventional microporous ZSM-5 zeolites are more selective toward mono-aromatics while the nano-sized and mesoporous ZSM-5 exhibited also high selectivity for (alkyl)phenols. However, the nano-sized ZSM-5 zeolite exhibited the lowest yield of organic bio-oil and highest production of water, coke and non-condensable gases compared to the conventional microporous and mesoporous ZSM-5 zeolites.

Highlights

Lignocellulosic biomass is considered as an alternative source of fuels/energy, chemicals and products, with the potential to replace, at least partially, the fossil raw materials, i.e., petroleum oil and coal (Huber et al, 2006; Triantafyllidis, 2013)
The thermal and catalytic fast pyrolysis (CFP) of lignin has been studied with emphasis on the effect of process parameters and type of ZSM-5 zeolite catalyst on the selectivity of phenolics and aromatics in the bio-oil
In the catalytic fast pyrolysis experiments with the ZSM-5 zeolite, it was shown that the higher temperature and the higher catalyst-to-lignin (C/L) ratio favored the conversion of the initially formed alkoxy-phenols to mono-aromatics, polycyclic aromatic hydrocarbons (PAHs) and alkyl-phenols

Summary

Introduction

Lignocellulosic biomass is considered as an alternative source of fuels/energy, chemicals and products, with the potential to replace, at least partially, the fossil raw materials, i.e., petroleum oil and coal (Huber et al, 2006; Triantafyllidis, 2013). The content of lignin depends on the type of raw biomass, i.e., 20–30 wt.% in softwoods (i.e., spruce, pine, fir, yew), 15– 25 wt.% in hardwoods (i.e., beech, aspen, birch, oak, poplar) and 10–20 wt.% in grasses, straw and stover. The structure and composition of lignin is related to the type of plant species, i.e., softwood lignins contain mainly guaiacyl (coniferyl alcohol) units with one methoxy group attached to the aromatic ring, hardwood lignins contain both guaiacyl and syringyl (sinapyl alcohol) units, the latter having two methoxy groups, while grass lignins contain p-hydroxyphenyl (p-coumaryl alcohol) units in addition to the G- and S-units (Azadi et al, 2013; Li et al, 2015)

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