Influence of bio-based solvents on the catalytic reductive fractionation of birch wood

ABSTRACT:The development of fundamentally new approaches for lignin depolymerization is challenged by the complexity of this aromatic biopolymer. While overly simplified model compounds often lack relevance to the chemistry of lignin, the use of lignin streams directly, poses significant analytical challenges to methodology development. Ideally, new methods should be tested on model compounds that are complex enough to mirror the structural diversity in lignin, but still of sufficiently low molecular weight to enable facile analysis. In this contribution we present a new class of advanced (β-O-4)-(β-5) dilinkage models that are highly realistic representations of a lignin fragment. Together with selected β-O-4, β-5 and β-β structures, these compounds provide a detailed understanding of the reactivity of various types of lignin linkages in acid catalysis in conjunction with stabilization of reactive intermediates using ethylene glycol. The use of these new models has allowed for identification of novel reaction pathways and intermediates and led to the characterization of new dimeric products in subsequent lignin depolymerization studies. The excellent correlation between model and lignin experiments highlights the relevance of this new class of model compounds for broader use in catalysis studies. Only by understanding the reactivity of the linkages in lignin at this level of detail can fully optimized lignin depolymerization strategies be developed.

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“…35 Our previous studies also addressed the advantages of using ethylene glycol under acidolysis conditions.…”

Section: Resultsmentioning

confidence: 99%

Advanced Model Compounds for Understanding Acid-Catalyzed Lignin Depolymerization: Identification of Renewable Aromatics and a Lignin-Derived Solvent

et al. 2016

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“…Such methods typically afford ah ighly-aromatic lignin-derived stream (whereby the most reactive functional groups have been deactivated through catalytic reduction, e.g.,c onversion of aldehydic intermediates into alcohols,a nd hydrodeoxygenation of ketones to methylene groups) and aholocellulose stream, as two distinct, stable and easily-separable fractions. [198] Thet wo predominant approaches for such upstream catalytic processing of lignin under mild conditions are hydrogenation and deoxygenation reactions,u sing either an oble metal-supported catalyst [273][274][275][276][277][278][279][280] or inexpensive Ni catalysts (notably,R aneyNi). [198,281,282] ECCL performed on Birch wood sawdust (Ru/C catalyst, 3MPa H 2 ,250 8 8C) has been investigated as amethod to tune Angewandte Chemie Reviews 8188 www.angewandte.org the alcohol functional group content of lignin oils.T he carbohydrate fraction is retained as apulp that is conducive to further upgrading, and the lignin fraction is collected separately as ah ighly aromatic oil containing up to 50 %o ft he carbon intake as mono-aromatics.…”

Section: Early-stage Catalytic Conversion Of Lignin As As Trategy Formentioning

confidence: 99%

“…Deconstruction of lignin may afford as olid carbohydrate pulp fraction, suitable either for undergoing full enzymatic hydrolysis into sugar monomers or for paper production ( Figure 7). [198,[275][276][277][278]282] Separation of the catalyst is important, so as to avoid contamination of the downstream products derived from the two streams.F urthermore,d ue to the strong possibility of poisoning by trace components in the lignocellulose feedstock, the catalyst must be relatively inexpensive.R ecent investigations have centred on the use of Raney-Ni, am agnetic catalyst. [198,282] This property allows for facile separation of the catalyst from both lignin oil and holocellulose streams.H olocellulosic fractions are obtained as predominantly catalyst-free solids that are highly conducive to further downstream treatment ( Figure 7A).…”

Section: Early-stage Catalytic Conversion Of Lignin As As Trategy Formentioning

confidence: 99%

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis

et al. 2016

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Lignin is an abundant biopolymer with a high carbon content and high aromaticity. Despite its potential as a raw material for the fuel and chemical industries, lignin remains the most poorly utilised of the lignocellulosic biopolymers. Effective valorisation of lignin requires careful fine‐tuning of multiple “upstream” (i.e., lignin bioengineering, lignin isolation and “early‐stage catalytic conversion of lignin”) and “downstream” (i.e., lignin depolymerisation and upgrading) process stages, demanding input and understanding from a broad array of scientific disciplines. This review provides a “beginning‐to‐end” analysis of the recent advances reported in lignin valorisation. Particular emphasis is placed on the improved understanding of lignin's biosynthesis and structure, differences in structure and chemical bonding between native and technical lignins, emerging catalytic valorisation strategies, and the relationships between lignin structure and catalyst performance.

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“…Technical lignin is burned because it contains highly recalcitrant CÀC linkagest hat render the material unsuitablef or selectived epolymerization to monomers. [11,20] Unfortunately,t hese lignin-derivedm onomers cannot be directly used as aromatic fuels (diesel additive) and fuel additives owing to their low volatility caused by the high oxygen content (20-25 wt %), which results in high boilingp oints (> 541 K). [11][12][13][14][15][16] RCF is typically performed in the presence of protic solvents at temperatures ranging from 453-523K using supportedt ransition metal catalysts (e.g.,r uthenium, palladium, or nickel) and hydrogen gas or other hydrogen transfer agents (e.g.,m ethanol,i sopropyl alcohol, or formic acid) as reductants.…”

Section: Introductionmentioning

confidence: 99%

Bifunctional Molybdenum Polyoxometalates for the Combined Hydrodeoxygenation and Alkylation of Lignin‐Derived Model Phenolics

et al. 2017

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Reductive catalytic fractionation of biomass has recently emerged as a powerful lignin extraction and depolymerization method to produce monomeric aromatic oxygenates in high yields. Here, bifunctional molybdenum-based polyoxometalates supported on titania (POM/TiO ) are shown to promote tandem hydrodeoxygenation (HDO) and alkylation reactions, converting lignin-derived oxygenated aromatics into alkylated benzenes and alkylated phenols in high yields. In particular, anisole and 4-propylguaiacol were used as model compounds for this gas-phase study using a packed-bed flow reactor. For anisole, 30 % selectivity for alkylated aromatic compounds (54 % C-alkylation of the methoxy groups by methyl balance) with an overall 72 % selectivity for HDO at 82 % anisole conversion was observed over H PMo O /TiO at 7 h on stream. Under similar conditions, 4-propylguaiacol was mainly converted into 4-propylphenol and alkylated 4-propylphenols with a selectivity to alkylated 4-propylphenols of 42 % (77 % C-alkylation) with a total HDO selectivity to 4-propylbenzene and alkylated 4-propylbenzenes of 4 % at 92 % conversion (7 h on stream). Higher catalyst loadings pushed the 4-propylguaiacol conversion to 100 % and resulted in a higher selectivity to propylbenzene of 41 %, alkylated aromatics of 21 % and alkylated phenols of 17 % (51 % C-alkylation). The reactivity studies coupled with catalyst characterization revealed that Lewis acid sites act synergistically with neighboring Brønsted acid sites to simultaneously promote alkylation and hydrodeoxygenation activity. A reaction mechanism is proposed involving activation of the ether bond on a Lewis acid site, followed by methyl transfer and C-alkylation. Mo-based POMs represent a versatile catalytic platform to simultaneously upgrade lignin-derived oxygenated aromatics into alkylated arenes.

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Influence of bio-based solvents on the catalytic reductive fractionation of birch wood

Abstract: In the reductive catalytic fractionation of lignocellulose, the choice of solvent significantly impacts the delignification efficiency, carbohydrate retention in the pulp and the macrostructure of the pulp.

Cited by 225 publications

References 72 publications

Advanced Model Compounds for Understanding Acid-Catalyzed Lignin Depolymerization: Identification of Renewable Aromatics and a Lignin-Derived Solvent

Advanced Model Compounds for Understanding Acid-Catalyzed Lignin Depolymerization: Identification of Renewable Aromatics and a Lignin-Derived Solvent

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis

Bifunctional Molybdenum Polyoxometalates for the Combined Hydrodeoxygenation and Alkylation of Lignin‐Derived Model Phenolics

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