Using 2D NMR to characterize the structure of the low and high molecular weight fractions of bio-oil obtained from LignoBoost™ kraft lignin depolymerized in subcritical water

Mattsson, Cecilia; Andersson, Sven-Ingvar; Belkheiri, Tallal; Åmand, Lars-Erik; Olausson, Lars; Vamling, Lennart; Theliander, Hans

doi:10.1016/j.biombioe.2016.09.004

Cited by 74 publications

(68 citation statements)

References 80 publications

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“…There is also a decrease in the methoxyl groups in the HO, which may imply that the aromatic rings substituted by a methoxyl group are involved in the formation of heavier Mw structures in the HO after accelerated ageing. The methoxyl groups correspond to a guaiacollike environment, as reported previously by Mattsson et al [38], with δ C /δ H 56.1/3.7-3.9 ppm which is in agreement with the spectrum of the chemical-shift database of model compounds (Table S1 and Fig. S2).…”

Section: Heavy Oilsupporting

confidence: 89%

“…8) were found to have a similar chemical structure to that of the fresh THF insolubles (Fig. S4), with structural motifs such as aromatic CH, vinylic/allylic linkages, a PAH-like structure, branched β-methyl groups (similar to tBu, iPr), methoxyl groups and minor signs of aromatic and aliphatic methyl groups [38]. This indicates that the HO structures have a different origin to those of the LO.…”

Section: Dee/thf Insolublesmentioning

confidence: 81%

“…5. These were performed based on the 1 H- 13 C NMR assignments of the model lignin-derived compounds in DMSO-d 6 and some references [26,[36][37][38][39][40][41][42]. These crosspeaks are related to the main types of aromatic products confirmed by GC-MS measurement.…”

Section: Gc-ms Analysismentioning

confidence: 99%

“…However, the structural motifs, such as aliphatic methylene (α/β-CH 2 ) and methyl (α/β/γ-CH 3 ) groups, and faint signals of methylene bridges (Ar-CH 2 -Ar) can be found together with aromatic -CH (Ar2, Ar5 and Ar6), alkene bridges (Ar-CH=CH-Ar) and PAH-like structures. Although a few aliphatic dihydroconiferyl alcohollike groups (Ar-CH 2 -CH 2 -CH 2 -OH) still exist, none of the typical interunit linkages present in native lignin can be detected [38,42]. The HO is generally assumed to be a macromolecule, the structure of which is mainly an aromatic network connected by alkene (vinylic and allylic-like) and aliphatic linkages (C2-C4).…”

Section: Heavy Oilmentioning

confidence: 99%

“…This indicates that the HO structures have a different origin to those of the LO. The aged HO_THF insolubles are assumed to be formed from the macromolecule structure in the HO, which has the same origin as the fresh THF insolubles, so they have a similar structural network to the fresh THF insolubles [38].…”

Section: Dee/thf Insolublesmentioning

confidence: 99%

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Thermal stability of low and high Mw fractions of bio-oil derived from lignin conversion in subcritical water

Lyckeskog

Mattsson

Olausson

et al. 2016

Biomass Conv. Bioref.

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The thermal stability of bio-oil influences its application in industry and is, therefore, a very important factor that must be taken into consideration. In this study, the stability of low and high molecular weight (Mw) fractions of bio-oil obtained from the hydrothermal liquefaction (HTL) of lignin in subcritical water was studied at an elevated temperature (80°C) for a period of 1 h, 1 day and 1 week. The changes in molecular weight (gel permeation chromatography (GPC)) and chemical composition (gas chromatography-mass spectrometry (GC-MS) and 2D heteronuclear single quantum correlation (HSQC) NMR (18.8 T, DMSO-d 6 )) of low and high Mw fractions of the HTL bio-oil (i.e. light oil (LO) and heavy oil (HO)) were evaluated before and after ageing. It was found that only a slight formation of high Mw insoluble structures was obtained during ageing at elevated temperature for 1 week: 0.5% for the LO and 3.1% for the HO. These higher Mw moieties might be formed from different polymerisation/ condensation reactions of the reactive compounds (i.e. anisoles, guaiacols, phenols, methylene (-CH 2 -) groups in phenolic dimers and xanthene). The high Mw insolubles in both the LO and the HO were analysed for structural composition using 2D HSQC NMR to obtain a better understanding of the changes in the composition of bio-oil fractions during the accelerated ageing process. In addition, a chemical shift database in DMSO-d 6 was analysed for a subset of phenolic model compounds to simplify the interpretation of the 2D HSQC NMR spectra.

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Section: Heavy Oilsupporting

confidence: 89%

Section: Dee/thf Insolublesmentioning

confidence: 81%

Section: Gc-ms Analysismentioning

confidence: 99%

Section: Heavy Oilmentioning

confidence: 99%

Section: Dee/thf Insolublesmentioning

confidence: 99%

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Thermal stability of low and high Mw fractions of bio-oil derived from lignin conversion in subcritical water

Lyckeskog

Mattsson

Olausson

et al. 2016

Biomass Conv. Bioref.

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Recent Advances in the Valorization of Lignin: A Key Focus on Pretreatment, Characterization, and Catalytic Depolymerization Strategies for Future Biorefineries

Mankar

Modak

Pant

2021

Advanced Sustainable Systems

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In this regard, lignocellulosic biomass (LCB) is an attractive alternative due to its abundant availability, carbon neutral nature, and its ability to produce a wide range of fuels and chemicals. [11,12] LCB mainly consists of cellulose (30% to 50%), hemicellulose (20% to 35%), and lignin (15% to 30%), interlinked with each other via a complex bonding network. [13,14] Currently, most of the biorefineries are focusing on the utilization of carbohydrates (cellulose and hemicellulose) for producing bio-ethanol and other chemicals. Moreover, lignin is the major by-product of pulp and paper industry with an annual production of 50 to 70 million tons. [15] However, lignin is mostly burned as a low-value fuel in the industries. [16] Interestingly, it is the only renewable source of aromatic monomers, thus making it a fascinating candidate to produce wide range of aromatics.Lignin is a highly complex 3D heteropolymer, consisting of methoxylated phenylpropanoid units (S unit, G unit, H unit), for providing structural rigidity to the plants. It consists of several COC (α-O-4, β-O-4, 4-O-5) and CC (β-1, β-β, β-5, 5-5) bonds and is interconnected to the cellulose/hemicellulose, thus making its biological or thermochemical conversion challenging (Figure 1a). [11,17] Therefore, the fractionation of LCB via different pretreatment techniques is crucial (Figure 1b). Majority of the pretreatment methods cleave COC (β-O-4) linkages of the native lignin due to their lower (218 to 314 kJ mol −1 ) bond dissociation energy (BDE) while stable CC bonds with higher (384 kJ mol −1 ) BDE are formed due to the recondensation reactions, thus modifying the lignin structure, which is named as technical lignin. [18][19][20] Lower BDE of COC bonds suggests that these bonds are relatively easier to cleave compared to CC bonds. However, depolymerization of native lignin is reported to give monomer yields of approximately seven times that of modified technical lignin. [18] Therefore, the development of new innovative pretreatment strategies that can preserve the β-O-4 linkages of the native lignin is highly desirable. Moreover, it is essential to get an in-depth knowledge of the structural modifications, occurring after the pretreatment, using the different characterization techniques like 1D/2D/3D nuclear magnetic resonance (NMR), 31 P NMR, solid-state NMR,

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In‐Depth Identification of Phenolics Fractionated from Eucalyptus Kraft Lignin

Wang

Zhao

Zhang

et al. 2022

Advanced Sustainable Systems

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Kraft lignin, the principal by‐product of the pulping industry, is an abundant yet highly underutilized aromatic resource. It is useful due to the vast scales involved as a source of fuels, chemicals, and functional materials when suitable postprocessing is applied. It is deemed to be a renewable alternative to fossil sources. Because of the extreme complexity of kraft lignin, in‐depth composition analysis and chemical structural identification are crucial for the development of effective valorization strategies. This work embarks on the characterization and identification of lignin‐derived phenolic compounds in representative hardwood (Eucalyptus) kraft lignin after selective fractionation using a single solvent. Advanced 2D heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR), 31P NMR, and mass spectrometry in combination with synthetic authentic compounds are used for the structural identification of the low‐molecular‐weight fraction of kraft lignin. A total of 20 phenolic compounds, including several novel monomers (catechols), dimers (diarylethanes, diarylethenes, etc.), and trimers with triphenyl structures are systematically identified in the Eucalyptus kraft lignin. In addition, polysulfide is detected in the low‐molecular‐weight fraction, indicating that the oxidative polymerization of S2−/HS− occurrs during the kraft pulping process. An improved understanding of kraft lignin, especially the low‐Mw fraction, is expected to provide essential information for the selective fractionation and valorization of lignin.

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Using 2D NMR to characterize the structure of the low and high molecular weight fractions of bio-oil obtained from LignoBoost™ kraft lignin depolymerized in subcritical water

Cited by 74 publications

References 80 publications

Thermal stability of low and high Mw fractions of bio-oil derived from lignin conversion in subcritical water

Thermal stability of low and high Mw fractions of bio-oil derived from lignin conversion in subcritical water

Recent Advances in the Valorization of Lignin: A Key Focus on Pretreatment, Characterization, and Catalytic Depolymerization Strategies for Future Biorefineries

In‐Depth Identification of Phenolics Fractionated from Eucalyptus Kraft Lignin

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