Structural changes in lignins isolated using an acidic ionic liquid water mixture

Brandt, Agnieszka; Chen, Long; Dongen, Bart E. van; Welton, Tom; Hallett, Jason P.

doi:10.1039/c5gc01314c

Cited by 179 publications

(181 citation statements)

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“…Depending on the biomass source, lignin accounts for approximately 10-30% of the biomass together with cellulose, hemicellulose, and other minor components (Chatel and Rogers, 2013). Lignin is a three dimensional polyphenolic biopolymer synthesized in plants mainly from coniferyl, sinapyl, and p-coumaryl alcohol (Brandt et al, 2015). These monomers give rise to guaiacyl (G), syringyl (S), and p-hydroxyphenyl (H) subunits via free radical polymerization (Brandt et al, 2015).…”

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“…Lignin is a three dimensional polyphenolic biopolymer synthesized in plants mainly from coniferyl, sinapyl, and p-coumaryl alcohol (Brandt et al, 2015). These monomers give rise to guaiacyl (G), syringyl (S), and p-hydroxyphenyl (H) subunits via free radical polymerization (Brandt et al, 2015). As projected by the 2009 Renewable Fuel Standard (RFS2) on basis of the 2007 Energy Independence and Security Act, the US alone will generate approximately 60 million dry tons of lignin annually from the capacity of cellulosic biorefineries by year 2022 (Tilman et al, 2009;Somerville et al, 2010;Brown and Brown, 2013).…”

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Catalytic Oxidation and Depolymerization of Lignin in Aqueous Ionic Liquid

Das

Shi

2017

Front. Energy Res.

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Lignin is an integral part of the plant cell wall, which provides rigidity to plants, also contributes to the recalcitrance of the lignocellulosic biomass to biochemical and biological deconstruction. Lignin is a promising renewable feedstock for aromatic chemicals; however, an efficient and economic lignin depolymerization method needs to be developed to enable the conversion. In this study, we investigated the depolymerization of alkaline lignin in aqueous 1-ethyl-3-methylimidazolium acetate [C2C1Im][OAc] under oxidizing conditions. Seven different transition metal catalysts were screened in presence of H2O2 as oxidizing agent in a batch reactor. CoCl2 and Nb2O5 proved to be the most effective catalysts in degrading lignin to aromatic compounds. A central composite design was used to optimize the catalyst loading, H2O2 concentration, and temperature for product formation. Results show that lignin was depolymerized, and the major degradation products found in the extracted oil were guaiacol, syringol, vanillin, acetovanillone, and homovanillic acid. Lignin streams were characterized by Fourier transform infrared spectroscopy and gel permeation chromatography to determine effects of the experimental parameters on lignin depolymerization. The weight-average molecular weight (Mw) of liquid stream lignin after oxidation, for CoCl2 and Nb2O5 catalysts were 1,202 and 1,520 g mol, respectively, lower than that of Kraft lignin. Polydispersity index of the liquid stream lignin increased as compared with Kraft lignin, indicating wide span of the molecular weight distribution as a result of lignin depolymerization. Results from this study provide insights into the role of oxidant and transition metal catalysts and the oxidative degradation reaction sequence of lignin toward product formation in presence of aqueous ionic liquid.

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confidence: 99%

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Catalytic Oxidation and Depolymerization of Lignin in Aqueous Ionic Liquid

Das

Shi

2017

Front. Energy Res.

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“…[21][22][23] Here we initially address this issue through the synthesis of 3 and 4, models of the LBHK structures. Previous syntheses of these types of compounds have included Hibbert's original route to 1 from homoveratric acid involving the use of diazomethane.…”

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The synthesis and analysis of lignin-bound Hibbert ketone structures in technical lignins

et al. 2016

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Understanding the structure of technical lignins resulting from acid-catalysed treatment of lignocellulosic biomass is important for their future applications. Here we report an investigation into the fate of lignin under acidic aqueous organosolv conditions. In particular we examine in detail the formation and reactivity of non-native Hibbert ketone structures found in isolated organosolv lignins from both Douglas fir and beech woods. Through the use of model compounds combined with HSQC, HMBC and HSQC-TOCSY NMR experiments we demonstrate that, depending on the lignin source, both S and G lignin-bound Hibbert ketone units can be present. We also show that these units can serve as a source of novel mono-aromatic compounds following an additional lignin depolymerisation reaction.

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“…4). Generally, this is due to condensation reactions between compounds cleaved from the native lignin and remaining oligomers chains [38,39]. In the case of the kraft pulping alkali-promoted condensation reactions take place forming alkali-stable linkages during the pre-treatment of the lignin [40].…”

Section: Technical Ligninsmentioning

confidence: 99%

Review on Catalytic Cleavage of C–C Inter-unit Linkages in Lignin Model Compounds: Towards Lignin Depolymerisation

2018

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Structural changes in lignins isolated using an acidic ionic liquid water mixture

Abstract: Recently, acidic ionic liquid water mixtures based on the hydrogen sulfate anion have been shown to effectively extract lignin from lignocellulosic biomass.

Cited by 179 publications

References 48 publications

Catalytic Oxidation and Depolymerization of Lignin in Aqueous Ionic Liquid

Catalytic Oxidation and Depolymerization of Lignin in Aqueous Ionic Liquid

The synthesis and analysis of lignin-bound Hibbert ketone structures in technical lignins

Review on Catalytic Cleavage of C–C Inter-unit Linkages in Lignin Model Compounds: Towards Lignin Depolymerisation

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